lb UKiueuily ~ KlU0Mlftu6ewtt ~ Kalwwf Hi6fMy

UNIVERSITY OF KANSAS PUBLICATIONS

MUSEUI"l OF NATURAL HISTORY

Copies of publications may be obtain ed from th e PublicationsSecret ar y, Museum of Natural Hi story, Unívcrsity of Kansas , Law­rence, Kan sas 66045

Price for this number : $6.00 postpaid

Front cover: The subspecíes of th c ridgenose rattlesnake[Crotalus icillan lt). Clockwise, starting from the upp er left, G. w.amalnlis, G. w. meridiana lis, G. w. silus, and G. u;. icil lard i. Allphotographs by [oseph T. Collins, wit h thc cooperation of th eDallas Zoo.

U NIVERSITY OF KANSAS

MUSEU~[ OF NATURAL H IST ORY

S PECIAL PUBLICATIO:'\ No. 5_________Dcccmb er 14, 1979 _

THE NATURAL HISTORY OFj\/IEXICAN RATTLESNAKES

By BARRY L. ARMSTRONGResear ch Associate

and

JAMES B. MURPHYCurat or

Department of HerpetologijDallas Zoo621 East Claretulon DrioeDcllas, T exas 7520.3

UKI\'EI\SITY OF KA:"SAS

L AW RENCE

1979

U l\"'!VERSITY OF KAN'SAS P UBLICATIONS

MUSEUM OF NATURAL HISTOlW

Editor: E. O, Wil eyCa-editor: [ oseph T. Collins

Special Publication No . 5pp. 1-88; 43 figures

.2 tabl esPu bl ishcd 14 Dcccmb cr 19í9

COPYIUGHTED 19i9By

i\ IUSEU), I 0 10' NATUHAL HISTOHY

U :\,I VEHS IT Y 010' K A:\'SAS

LAWHEXCE, K AXSAS 66045U.S.A.

P II/ :-'-TED ByU:\ I\'E lI SIT Y OF K AK SAS Pruxrrxc SEI\"IC E

L AWRE :-'¡C E , KA." SA S

ISBN : 0-89338-010-5

To Jonathan A. Campbellfor his encouragement

PREFACEBeginning in Novcmbcr, 1966, stud ies on rattl esnakes (genera

Grata/lis an d Sistrurus¡ and othe r pit vipe rs were initiated at th cD alI as Zoo wh ích includcd techniques for mai ntenance an d diseasetreatments, in conjunction wi th obscrva tions on ca ptive anel wi ldpopulat ions. Main tenance tcchniques and elisease treatm ents havebeen pu b lish cd in an ea rlic r co nt rib u tion .

The result s of our stud ies on th e ecology an d natural h ístory ofMcxica n ra tt lesnakes are con ta ine el in th e present accou nt . Sincenu rnerou s h eh avioral seq ue nces wer c difficult to record in th e field,man v rattlcsnakes w cre main ta incd in the labora torv . O ver o nehuncÍred aneI tw enty-five cap tive individuals, comp risí ug over 50tax a (inc ludi ng fonns inelig enous to the Un ítc d Sta te s) wcrc avail­able for stuely.

' Ve havo a tt empted to sho w the value of a m ultiface tcd ap­proach to th c stuely of a body of organisms h y beginni ng wi th fielelobs erva tio ns as a b asis for undcrstauding, Ioll owcd b y main tc nancein th e ca ptiv e state whercupon specimc ns can b e pl aceel uponeleath in a sys ternatic mu seum co llectio n. This a rrangem ent allowsan in vesti gat or to exami ne va rious as pccts of an an imal 's "b cing"by recording da ta which would be virtu all y impossible to recordin th e ficlel. F urthcr, this combinccl a pp roach maxim izcd our ahili­ties as one of us is sorncwhat inco mpc ten t in th e ficld aneI the othcris an e rra t ic animal kccper.

T he assistance anel co ope ra tio n of many perso ns cont rih u tc cl tothe eompletion of this study. For va rious courtesics extende d tous , w e thank Hay Ashton, James P. Bacon, Hobcrt L. Bezy , Ch a rles~1. Bogert, David Brown, ~I a ry E. Da\\"SOl I, J .S. D obhs, M íchaelS. Eelwarels, Thomas H . Fritts. Ja mes c. G ilIingham, Honald Goell­ner, H arry , V. Creen c, H crb ert S. l Ia rri s, Charle s l Iocssk -, T erryHulse y, J . P. Jo nes, T homas L. Jarcia n, Joh n E. [oy. Tommy Lo gan,Ar th ur Lo pez, D anny Lopez, Ed warcl Xlaruska, H ymcn Ma rx,Robcrt " ' . ~ 1urph y, G eorge R. Pisan i, th e late Louis Pistola , T horn asPortcr, Stcvc J . Prchal, Peter C. Prit ch a rd , W ill iam F . P yburn ,George B. Rabb , Charl es \V. lt ad cl ííle , Vincent D . Roth, ThomasSchu ltz , H obart ~ 1. Smith , Bnrney Tornberl in. Tom Va n D evcndcr,R. W ayne Van D evendcr, James W alk er , Tim W alk c r, John ' V.W right, Rich a rd G. Zw eifel , and our many frienels throughou tM éxico.

W e are gra teful to \Valter Auffenberg, Charles M . Bogert ,Charles C. Carpenter , [ oseph T. Collins, Hoger Co ua nt, James R.Di xon, Williarn E. Duellma n, th e late H oward K. C loyel, M íchaellIerron , D onald \V . Moorc , Joh n A. Sh adduck, and th e late E dward

v

\

H . T aylor fo r reading and crit iciz ing the manuscrip t and offeringmany helpíul sugges tío ns. Photograph íc assis ta nce was offe red b yR. T crry Basey, M . Gra nger, W aync Seife rt , and Joh n H. Tashjian.The able sta ff of th e Dalias Zoo D cpartment of H erpctology, DavidG. Barker, Ra ym oncl K. Guese, \ Vill iam E. Lamoreaux, anel LyndonA. Mitch el l have recorclecl numer ou s ob servations ancl h ave con­tributecl to th e overa ll main te na nce of the rattl csnakcs d iseusseclth ro ugh their en thusiasm and expert ise. The librarian staff ofInst itu to Butant an in Sao Paulo assisted lIS in n umcrous ways.Variou s perso ns associa te d wi th th e Univc rs ity of T exas Press,specifical ly Ann H idalgo Manl cy, Ph ilip L. \ Vagn er, Rob ert Wau­chope, and Robert C . \Vest , a lIowed us to use figures from lland­hook oi blidd!e A me rican Indians. Ralp h R. \ Voocliwiss an d AntonS. Prechtel of th e U.S. Departm ent of Commerce, N atio nal O cean ícan d Atm osphe r ic Adminís trn tion , Washi ng ton , D .C. , p rovid ed cli­ma tic infon n ation and alIowecl us to use m aterial from Climaie oiMexico by [ ohn L. Pa ge . Se ñor Silvino Agu ila r Anguia no , Subdi­rector Gral. de G eografía y Meteorolog ía , se nt climat íc data andnumerous maps fo r ou r use. Memb ers of th e D all as ZoologicalSoc ie tv, through thc efforts of Bernard Brist er, provid ed partialtravel expenses.

The ard uous task of typing ce rtain parts of th e manuscript wasch eerfu lly accompli sh ed b y Kathryn Campbell, [ anet [ack son ,Martha, F. Murph y, Verna S. M urph y, ancl Myr a Smith . D ebBenn ett skillfu lIy execu te d th e dra wi ng of th e map of M exíco onthe inside back cover ,

F inally, specia l recogni tion must b e extended to Jon athan A.Campbell, who in so many ways aided us in th e p reparation ofthi s manusc rip t. H is unflagging enthusiasm in th e field, th e gener­O \lS donation of specimens un der h is ca rc, h is th ou ghtful co mmentsan d criticisms of th e manu scrip t, h is photographic ab ilit ies andovera lI enconragement made the completion of this study muchmore enjoyab le for us o For th ese reasons, we have dcdicated thisstudy to h im.

Barry Lo Arms trong and Jam es B. Murpln)Dalia s Z ooDalias, T exasMnrcli 1979

VI

CONTENTS

PACErNTROD UCTION __ _ 1GENERAL D ESCHIPTION OF TH E HE GrON 1MATERIALS AN D :ME T H O D S 3ACCOUi\'TS O F SPE C lES

Crotalus atrox Baird and C irard _ _ 4Crot alus hasil iscus (Copc) 6Crotalus cataline nsis Cliff 8Crotalus cerastes Hallo well 9Ctotalus durissus Linn é 10Crot alus enya (Cope) 16Crotalus int erm edius Troschel _ _ 18Crotalus lenulus ( Kcnnico t t ) 22Crotalus mitchelli (Cope ) .____ _ _ 29Crotalus molossus BainI and Girard _ _ 31Cr otalus potij sti ctus ( Cope) 34Crotalus pricei Van D cnbur gh 38Crotalus pusillus Klauber __ _____ _____ ._ _ 43Crotalus ruber Cop e _ . 46Croialus scutulaius ( Kennicott ) 48Crotalus ste inege ri Dunn _ _ . 50Crotalus tigris Kenni cott 50Crotalus tortugensis Van Denburgh and Slevín 53Crotalus t.ranscersus T avlo r 53Croialus triscriatu s ( Wa'gler) .56Crotalus cirid is ( Hafinesque ) ____ 61Crotalus iclllarcli Xlcck _ 63Sisirurus ra vll s ( Cope ) 68

DISC USSION iüHESU~IEN __ _ iiAPPEi\'DIX : H:\ 1\'G E O H ALTIT UDE EXTE1\'SIO:\S

HEPOHT ED Ii': TE XT __ i8LITEH AT UR E C I1'ED i9INDEX 1'0 H ERPET OLOGI CAL SClE:\TIFl C 0: A ~ I ES 86

vii

INTRODUCTIONThc view th at thc ce ntral pl a teau of Mcxico was th e center of

disp er sal for ra ttlesnakes is a zoogcograph ical position neccling nodefen se (Cloyd 1940, Srni th 1946). H owcver, infor mati on rel at ingto man y species, particula rly the pri mi tiv e monta ne for ms, is limi te d ,Ther e are few observations dcali ng w ith th e ecology an cl na turalh ístory of Mcxican rattl esnakes ow ing mainly to th e inaccessi bi lit yof many of thc populations. Mexica n ra ttlesnakes inhabi t many eco­logical nich os ra ngi ng from xeric to mesic env ironmeuts. O ne spe­cíes, Grata/lis triseríatus, reaches alti tu des of 4573 m (Klauber 1956).Man y mai nland form s are found in th e ce ntra l Mexican plat eanwhcre th ey tencl to be restrictcd to ar íd , roc ky situations, Othcrspecics a re found in lowl and desert habitat s, incIuding islaud popu­lations of th e Gulf of California.

The pu rpose of thi s study is to : (1) analyze ami dis cus s th eenvironme ntal compoue nts (includ ing physiography, vegcta tion , amiclirn ate) of Mexico a nd their cílcct on thc d ístribu tion of rattle­sna kes, and (2) recorcl obs erva tions of na tural an d ca ptiv e po p­ulations.

GENERAL D ESC RI PT IO¡ O F T HE REGl ON

Information recorcled b y Gold ma n (19.51) serves to illustrat e th eph ysícal cha rac teristics of Xlcxico (F ig. 1). Barbour (1973) prcsentsa dctailcd dcscri pt ion of the centra l mesa , an d ~ lorafka (1977) de ­scribes th c C hi huahuan D escrt. In ord cr to un dcrstand th e cu rrcntgc olog ica l pattcrns of Mcxico and th c gcohistorical dcvelopmentand pal eogeography, th c rcadc r is ref crr cd to Ma ld onudo-Kocrdcll(1964) and W est (1964). Soil h as hccn trcatccl by Stcv ens (1964).

The rca der should co nsult suc h ll1aps as those includccl in th eworks of Cout reras Arias (1942) an d Il crnandez (19:23) for climaticda ta . Inform at ion on wcathcr an d climate is sununarizc d b y Viv ó(1964). Sh rev e (1944) d iscussed rainfalI pa tt erns in Mexico, no rthof th e Tropic of Can cel'. Refer to Fig. 2 for th e mean annualrainfalI in M éxico.

Na tural vegeta tion in Middlc America is d epictecl in Fi g. 3.D etailed accounts of thc vegetati onal relationshi ps for variousMexican a rcas are as follows: Bcard (1944), Brand (1936, 1937,1957), D uell man (1965), Egglcr (1948), Ge ntry (1942, 1946a, 1946b),Coldman (1916), Go ldman and Moore (1946), l lold rídgc (1947,1964), Leavenworth (1946), Leop old (1950, 1972), Lesueur (1945),LundelI (1934, 1942), MacDou gal (1808), Ma rt ín (1958), Mart íncz(1945), Mi randa (1942, 1952-19.53), Mi rand a an d Sharp (1950), i\lul­ler (1939, 1947), Nelson (1921), Savage (1960), Sharp (1946), Sh reve(1934, 1937a, 1937b , 1939, 1942, 1944), Sta ncllcy (1920-19:26, 1930),Wagner (1964).

2 SPECIAL PUBLlCATION-~lUSEml OF NATURAL HI STORY

"'II

+-

- -T-

(MI/BBEAN

Fr c . 1. Ph vsiographíc region s of ~lexico. Reprinted from Hand book 01Middlc American l nd ians. Copyrigh t 196·4 by Uni v. Texas Press. Used bypermission of Robert C. West,

FIC . 2. Mean annnal rainfall ( rnillimetc rs ) for Mexico. Reproduccd bype rnu ssron [rom the NationaI Oceanic and Atmosph eric Ad ministra tion,W ashington , n.e.

TIlE NATU RAL HISTORY 01' ~IEXICAN RATTLESNAKES 3

FIG. 3. Na tu ra l vegetat íon of Mexico. Format íons classí ficd aft er Beardan d ot hers. Rep rinted Irom l landhook 01 Middlc Am crican l udiau s. Cop y­rig ht 196-4 by Unív. T exas Press. Use d by permission of Phil ip L. W agner.

~I ATERIALS AN D ~ IETHODS

Most of th e localities whic h are list ed in the foJlowing speciesaccounts are bascd on our own obs ervations un less o th erwisc spe ­cified, altho ugh voucher specimen s werc not collecte d in manyinstances , Since th e primar)' pu'1)OSC of th e study was not to collec trattlesnakes for sys tematic collec tions, man)' of th e individuals ob­sc rve d wcre not coJlecte d and in so rne cas es, parturient Icmal eswere hel d until th ey gave b irth th en rclea sed with th e yo ung at th esarne locality. Li tters of snakes wcrc 1I0t measured and weigh edin th e field . In the Iaborat ory, weights wcrc rccordcd with an Ohaustriple-beam balance. Measuremeu ts werc made on newborn snakesin most cases , usin g th e meth od described b y QlIinn and [ ones(1974),

Snakes th at were remo ved fro m wild popuIations have b eendeposit ed (or will be up on th ei r d eath) in th e Iollowing vcrtebrat ccollec tions : Unive rsity of Colorado (Ue \ I), Dalias .\Iuseum ofNatural H ístory (D .\INH), I-Ierbert S. H arris/ Robert S. SimmonsPrívate Co llec tion (H SH- RSS), University of Kansas Mu seum ofNatu ra l H ístory (KU), an d Un iversit y of Texas at Arli ngton (UTA).Each museum number refers to an individual spe cimen.

THE 0:ATU RAL HI STORY OF ~IEXICAN RATTLESi\'AKES 5

sured ca. 1.2 m total length. The cou rts hi p b ehavior det ailed belowwas typ ical for C. atrox ob ser vations made b y u so

0900h The female was plaeed wíth th e ma le.0901 The ma le sensed her pr esenee an d began rapid tongue fliekin g

(1 pe r see ).0906 Th e female responded dcfens ívely for a Iew minutes, but began

to reaet to maleo0911 Male raised an terior th ird of body 5-6 cm above th e surface. Spas­

modic jer king of ma le was apparen t th rou ghout enti re period (1every 2 sec) an d íncrease d to 1 per seco

0917 Male sta rte d rapid ten gue fHeking on closest part of bo d y and be­ga n to inves tigare entir c lat e ral and dorsal body surfaee of female.j erking of ma le became more int ens e ( 2 per 3 sec ) . }Olale held headat 45 ° anglo with men ta l sca le touching dorsum of fem ale. Head ofmal e p ressed against dorsum of Icm ale, and side -to -side motions(approx. 2.5 cm ) were undertaken in clu ste rs ( 4-5) at irregularínterva ls.

092 7 By movíng in an an terior pl ane, male began to dr ap e lar ge radiuscoils over female.

0931 Sequ en ce Iasted un til mo st of ma le's body was in con tac t withfemale. Male att em pt ed to insert hem ipe nis but no externa! e vers i ónof hernípenis wa s in evide nce. Both sna kes lift ed the tail s at th eloca tion of the cloacae and occas íonallv Ilickcd th e ta ils with aside-to -síde mo tion . The subs tra to was ' not touehed bv th e tails.Male cons tantly mo ved ta il in an atte mpt to a lign cloacae. Whencloacae werc juxtapos cd , ma le tricd to sliclc tail under ta il of Icmale.

0951 Cloacae were align ed and ma lc inserl cd. During th e latt e r part ofcourtship activity , female hegan twit ching with sam e Ircqu ency asma leo jcrking and twitching stoppe d wh en mule insc rted , Cour tsh iplasted 20 min and no movem eut othe r th an stcady p ulsat íon of thebod y near male' s tai! wa s in evi dcn ce after pene tration. Bot h sexeswould occas íonall y drag each other slowly by the attaehed hem í­penis; this behavíor perhap s was in iliat ed hy exte rna] st imuli.

Act ua l copula tion lasted from 2-8 hours. Breeding dates wer erecordcd from 21 .T an uary to 26 .T anuary 1974 .

Variation of pre-coital b chavior was ob served on 28 Fcbruary1975. D ur ing th e courtship pcr iod , the mal e w as loosel y loopedover th e Fema le an d un dulated slow ly, In aclcliti on , th e male tri cdto positi on h is tail und er th e cloaca of th e female. I n coutras t toth e beh avior observed previously, th e fcmale raisecl her tail andrepeat edly opened her cloaca. \ Vhen th e cloaca e we re juxtaposccl,th e male inserted hi s h eiuip cnis bu t no external extrusion of th ehcmípcni s was no ticed. The ma le exhib ited pulsating throbs (onceevery 3 seconds ) inte rmi ttentlv and th e snakes wcre in copula tio nnearl y 7 hours. The female remainerl pa ssiv e thron gh out th e re­mainder of th e scquence. When th e sn akes w cr e placed in a largerunit (1.0 X 0.8 X 1.2 m high ), th e female assumecl a vertical an te riortrunk posture as th e ma le clirected courtship behavior to h er. T hismay be a fem ale rejec tion post ur e. Of nin e captive litter s, t",a\Ver e born in June, one in .T ul y, three in August, t\Vo in Se ptemberancl on e in October. Sexual maturity \Vas reached in 30-36 months.

4 SPECIAL PUBLICATIO~-~IUSEU~l OF NATU RAL HISTORY

ACCOUNTS OF SPECIES

Crotalu s atrox Baird and Girard

Crotalus atrox is one of th c lar gcst and most aggressívc of th eMexican rattlesnakcs ( Klauber 1972 : 448 ). Although it has beenconfusc d with C. scutulatus ( Klaubcr 1972 : 541 ) , C . atrox is gen­erally wcll kn ow n throughout its range. These rattl csnakes arefou nd in a wid e variet y of habitats at varying el evations. Snakesfrom southern Oaxaca (C loyd 1940: 206; Klauber 1952: 102) andce ntral Veracruz (Klauber 1952 : 103) present problcm s in C. atroxdi stribution.

Specimens obta ined b y lIS are from th e follow ing loc al ities :BAJA CA LI FO Ri\ IA : Progreso, SOl\'O RA: 4.8 km S Sonoyta,Caborca, Esqueda , CH I HUAHUA: 16-32 km S Chihuahua (4 spe­cimens), nea r El Sueco; NUEVO L EóN: 16-48 km NE SabinasH idalgo (10 specimens).

In Mexíco, C. atrox inhab íts deserts, pl ains, g rass lands , and Ioot­hill s from ncar se a level at La Po sa, Sonora (T aylor 1936: 497) toat lcast 2440 m nea r Alvarez, Sa n L uis Potosí (Klauber 1972: 5:27).Indivídual s a re gcne rally Iound in aricl country and are not neces­sari ly assoc iate d w ith rocks, Mcsquite, dr'y w ash banks, creosotebushes, a nd bu rrows provid e likely retrcats. Taylor (1936: 497)found thi s snake common along th c seashore wher e sh rubs aneIsandy beach es met. \Vc fou nd C . atrox especially pl cn t íful in mes­qu ite grass lands no rth of Sabinas H id algo in Nu evo León . Sev eralsnakes ha ve bcen observe d in this arca along road s at night duringth e hot sumrn er months. Hardy aneI ;"lcDiarmid (1969: 213) con­side red thi s spe cies to b e rather un common in thc lowlands of ex­trem e northcrn Sinaloa , and R. T . Busey (pers. comrn .) stated thatC. basiliscus was mu ch more com mo n th an C . atrox in th c nearbyÁlam os a rca of sou them Sonora. In northern Sonora, near Esqueda,th ese snakes are not un common in sa ndv, creosote habitats.

Through out its ra nge, thi s ra tt lcs uake is mo stly nocturnal , atlea st dn ring th e sum mer mo nths . xl ost sna kes obtaineel by us haveb ccn collccte d w hile crossin g roads during th e carly ovening . Som eindivid ual s hav e been see n in th e carly morning or on cloudy days ,but th ey are ge nerally not ac tiv e and a re usually coil ed in th emo uth of a burrow or under the cover of available brush .

W e hav e observed rituali zcd corn bat between mal es in captivity.W iley (1929), II ocsslc (1963) and Petzold (1963) have discussedreproduc tivo biology and mating b eh avior in this spe cies. W e ob­served cigh t C. ai rox courts hip sequc nccs in capt ívity and a gen­era l patt ern wa s apparen t. The cnclosure in which obs ervutionswere made measured 80 X 40 X 40 cm hígh, and th e snakcs mea-

6 SPECIAL PUBLICATION-~IUSEU~ I OF NATU RAL HISTORY

Litte r size varíed fr om six viable you ng (4 infertile egg masses) tol 5 viable young ,

Vegcta t íonal characteris t ics associa te d with the habitar of G.ai rox in Mexico inciudc th e Season al Fonnation Series, the Steppe,Thicket un d Scrub Desert as d efined by W agner (1964). Cloyd(1937) aneI Lowo (1964) d escribed th c fauna l a rcas inhabitcd b yth is species in Ari zona.

Crotalus liasil iscus ( Cope)

C rota lus b asili scus b asili scus. C rotalu s l). basiliscus is on e ofthe Iarges t aneI gent lcs t of the Mexican C rotalus. Cloyd (1940: 161),Bogert a ud Oliver (1945: 394), and Kl auber (195l : 87) have co rn­mente d on its sta tus in re la tionshi p to G. 1Il0/0SS11S. As far as isknown, the clistribut iou of these two species usua lly does no t ov er­lap, b ut H ard y an d ~lcDiannid (1969: l 16) gave reasons for b e­lícving tha t the two species live sy m pa trically in northern Sinaloa .Furthcr ínvcst igat ion is necossary in thi s ar ea . Klau b e r (197:2) in di­ca tes an overla p in the ranges of G. !J . oaxacus an d G. 1/I010sslI snigresccn s in Oaxaca . \ Ve hav e foun cl G. !J . bosíli scus to be a COIll ­

mon snakc (30 specime ns) of Xlexicos w est coas t wi th in dividualsbeing observed in tropi cal th orn for est s and , to a lesse r degrec, intr op ical dcciduou s forest s.

~ fany records of G. /J. basiliscus are avai lab lc, no doubt owingto th e fac t th at thi s ra t tles nake is vcry common. Exam ples of thissnake are kn own from ex treme so uthcrn Sonora, sou th th roughSinaloa, Nayarit , Jali sco, Colima, an d weste m M ich oac án w here itsra nge apparent ly termin ar es at the R ío Balsas. 1t would no t b esurp rising, how ever. to find this ra ttIcsna ke on thc coas tal pl ain ofGue rrero where topographical sirni lari ties to its known habitat areapparent. Spccim ens ob ta ined b y li S a re from the fo Ilowing 10­ca lit ies: SIN ALOA: 4 km S Santa Lucía, 5 km \V Concordia;l':A YARIT: 4.8 and 8 km E San Bia s; JALI SCO : 8 km 1\ CiudadGuzmán, T amazula , 1'. flCHOACA N : D os Aguas.

Grata/lis 1J. basiliscus is ge ne ra lly a Iowl and resídcnt inhabitingthe previous ly mentioned trop ica l thorn or trop ical d eciduou s for­es ts. Klaubor (197:2 : 5l8) re po rtc d th a t a specimc n fro m Apatz iug án,xli choacán , was co Ilecte d at 975 m elev atio n in th e arid tropicalscrub for est. 1le fe lt this to be th e IIpper lim its of the a lt itud inalrange of this form , but he w as no doubt unfami liar w íth the speci­men from 19.1 km :t\E Santa L ucía in Sin aloa (KV 78966) w h ichwas collected at 1940 III in a humid p ine-oak forest o \Ve ca n exte ndth e altitudinal limits wi th a recentl y co llecte d specimen (V C \ f5 1.3 1.'3) [rom near Dos Ag uas, 1'.1ichoac án. T h is snake w as Found inJlll y 1974, w ell w ithin th e co nfines of the Sierra de Co alcom án atan e leva tio n of :222.5 m. T he rat tles na ke w as located w ithi n 3 mof a stream in a canyon bottom in th e h umid p ine-oak forest. Local

TlIE NATU RAL HISTORY 01" ~ IEXICAN RATTLESI\'AKES 7

residents rccognized th e individual , but rep ort ed th at C. b. liasil iscuswas not ncarly so common as th e abundant C. pusillus or the fairlyrarc C. durissu s culm inatus . Dcspitc the fa ct that occasional snakesmal' reach elevations abo ye 2000 m, we consider such occurrencesrare, for C. h . hasili scu s is appa re utly a lowland fonn . Most of ourspecime ns ha ve come from bclow 1000 m in va rious tropical fores ts(see Hardy and Mcfriarmid 1969: 51-SS). Anothcr snak e (UTAR-6120) wa s found on th e south slope of Cerro Bar alosa in theSierra de Coalcom án. On 21 july 1976, an individual snake (UTAR-6071) wa s found coiled in shade among rocks at 91.5 m at Plomo­sas, Sinaloa, in a transition pin e-oak and tropi cal decíduous fores t(Fig. 4). This snake was coll ected in thc same rock slide as anexample of Crotalus ste jnegeri. C. h, basil iscus appears to be mos tcornmon, or at least most ac tive , during thc summe r rain y season,and most individuals are located crossing roads. Hardy and Me­Diarmid (1969: 214) reported tha t th ese rattlesnakcs hael also beenfound in thc dry scason in Sinaloa , al though thi s is thc pcriod ofleast acti vit y.

Vegctative com ponents associated wi th thi s rattlesnake are th eArid Tropical Scrub F orest (Duellman 1965) and thc Tropical ThornForest and Tropical Deciduous Forcst as defin ed by Leopold

1"1<; . 4 . Habítat of Crotalus ha siliscu s basiliscu s, C. lcpidu s niacu losus andC. stcincurri near P lomosas, Sinaloa , Mexico, Septe mber 1976. C rota/lis /.nutc ulosu s occurs in the p iue-oa k Forest co ver inj; th e lop of the bln ffs. Crotalu sstciuegcri an d C. h, hasiltscu s a re Iourul in th e trop ical dccid uous fores t onth e lowe r hill sides an d th e transiti on zo ne a t th e base of the b luff s, ( Pho to­graph by Jona than A. Campbcl l. )

8 SPEC IAL PUBLICATI O:,-:- :-. ru SE Dr\1 OF NATU RAL HISTORY

(1950). According to G oldman (1951), rn esquites, acacias , wild figs,Spanish cedar, palo m ula to (p rob ab ly Bursera grandifolia), wíldguava (Psid iu ni guaiac a), Castilla elas t ica, silk-cott on trees aneIpalms grow in the area in hab ite d b y thi s rattlcsnake.

Crotalus basili scus oaxacus. A Oaxacan subspecies, C . b. oaxa­Cli S, separatcd ge ograp hically from C. b . basili scus b y the entirestatc of Guerrero, is a ra the r ncgl ect ed form fr om the interior h igh­lands of ce ntra l Oaxaca, D escribed in 1948 b y Clo yd fro m tw ospecimens, th is subs pecies has rernained rare in syste matic collec­tions. Much of the vegetat ion in th e a rea once inhabite d b y C . b,oaxacu s is now eithe r d estroyed or near d est ruction. This rattlesnakewas appare ntly quite co rn m on in the Va lley of Oaxaca, but is nowrarely encountered there, mos t ind ividuals now b eing taken fromth e mou nt a ins surrou ncling Oaxaca. T hese mounta ins exh ib ir t ypicalp ine-oak habita t where roek ou tc ro ps ar e occasio na lly Iound, aneIth ese area s are su pe rficia lly similar to the h ábitat of C . uiolossus.Thcy seem to p ref er the more heavil y for ested arcas and , accord in gto th e local p cople, are ofte n scen among ro cks where C . interm ediusglo!Jdi is Iou nd. T he first specimen ob taine d by us frorn E l T ejocote(also known as Tejoco tes ) w as located on a ste ep hillside w ithin th epi ne-oak forest at 2.438 m . \ Ve had previo usly co llec ted in this arearather extensívcly for th ree ~'ea rs, and th is w as th e Hrst exam pleof C . b , oaxacus we liad encoun tc red . A sccond sp ec imen w as se­cu red along the Río Co lorado nea r E l T ejocote durin g the firstw cek in February 1976 at an elc va tion of 1982 m (J. A. Cam pbell ,pers. co mm.). Anot her w as colle cte d on 24 M arch 1976 in a pine­oak fores t a t an elevation of 2285 m (UT A H-6820). An individual(UT A U-6060) was fo und killed on th e ro ad on 31 [ ul v 1976 a t 1030h in an oak fores t (1932 m) at 3.5.5 km 1\W T elix tlah uaca.

C. b. oaxac us in habi ts th e Montano Fonnation Series aneI Mon­tane Thícket as d efined by W ag ne r (1964) and Pi ne-Oak Forest(D uellman 1965).

Crotalus catalinensis CJiff

Crotalus cataiine nsis is fou nd only on Santa Catali na Island,Baja California elel Norte , an d is related (ecolog ically) mo st closelyto C. ruber lu casensis. The islan d is rocky aneI barren wi th sparseb ru sh anel cacti (Kla ub er 1972). The tempera tures of th e co astalislanels ar e simila r to the ad jacent mainland (Nelson 1921),

O ne of th e ma le snakes mainta ine el by lIS , born duriug September1975, exh ib ite d heael-bobb ing and tongue-Hícking courtshi p b e­havior toward a nother individ ual (KU 173096). Ano ther pair copu­lateel on 15 january 1978. T hi s ra tt lesnake is found in th e Seaso nalForrnation Series anel Cactus Scrub as d efin ed b y W agn er (1964).

TIIE NATU R.AL HI STORY OF ME XICA:-': RATT LESNAKES 9

Crotalu s cerastes H allowell

Thc two subspecies of thi s ra ttlesna ke th at occur in Xlexico,C . c. laterorcpeu s and C. c. ccrcobo mbus will be rcferred to as C .cerastes, since th eir habitat s, habits, an d behavior ar e essentially th esamc . Approximately 300 ind ividuals h ave b een observed by us onth e eas te rn drainagc of th e Sierra [ úarez an d Sierra de San PedroM ártir as far south as Pu ert ecitos, a fishing village on th e GuIf ofCalifornia in Baja California d el Xorte. In Sonora, C. cerastes islocated north an d wes t of th c Nognles-Herrnosi llo-Cuaynuis high­way (Route 15), with th e heaviest concentration of snakes beingIound in th e D esierto de Altar, a n arid sandy desert in the ex trem enorthwest part of th e state .

Crotalus cerastes genera lly prefers the sandy arcas of its clesertenvironment , altho ug h it is not restricted to that particular habitat.D am mann (1961) reported th at C. cerastes p opulat ions may be af­fected by th e amount of vege ta tio n presen t. In Arízona, th c popula­tion den sit y of thi s rattlesnak c tended to de crease as th c veg etntionincreased. Too much vegc ta tion may limit the unique locomotorabilities of thi s spe cies. These rat tlesnakes can be found on hardstony terrain , such as th e Co t tonwood Springs arca of [oshua TreeNat ional Monument. These part icular ind ividuals are not as com­mon as those Iound in sandy si tuations, but th ey appcar to b eslightly larger in body girth. T his may be dil e in part to a diff er entdi et as mammals rather th an lizards ar e more plentiful in theseareas. This terrain also has a more luxuriant growth of desert vege­tation . Gen erall y, C. ceraste s will commonly be fOUJHI on sandyalluvia l fans, sand dunes, sandy washes, and th e frin ges of desertdry lak es. The greates t concen trat ions of th ese rattl esnakes ar eusu all y found in areas w here wind-blown sand form s srnall moundsat th e bases of creosote bushes (see Brown 1971). \liller and St eb ­bins (1964) [ound C. cerastes resting undcr bushes. Thc arcas a roundSan Felipe, Baja Californ ia , Yumn , Arizona, and ;\!exico Route 2between Mexicali and Sonoyt a ar e goo d examples of thi s type ofhabitat. In th ese sítuatio ns. C. cerastes is easilv located, usuallv atthe mouth of a burrow, or beneath bushes whe;e shade is availahle.One snake from north of Puerto Peiíasco, Sonora, was Iound in acreoso te bush about 30 cm aboye th e sandv soil . This individualappe ared to be basking rathcr than hunting, as th e specimen wasnot alert and did not seem to sense our presence. In th ese ar easthe sand shifts cons ta n tlv and C. cerastes is oftcn obs ervcd coilcdnear a bush , partially c¿ ncealed by sand. Browu (1971) suggest edth at th e unusual cra te ri ng b eh avior serves primaril y for th cnno­regul at ion an d scco ndari ly for concealment during th e da y, whereasat night th e reverso is t ru e. Tndíviduals have al so been foundwithin and under th e wreckage of di lapidated buildings wher e as

10 SPE CIAL PUBLICATION-i\lUSEm,1 OF NATURAL HISTORY

ma ny as five specimens have b een locatecl in on e sea rch . Thisra ttles nake is mostly nocturnal but may b e seen cluring th e d ay inearly spring and la te fa llo Activ íty cycles seem to b e related pri­maríly to th ermal cons idera tions (Brow n 1971). Moore (1976) sug­gestecl that du e to circula tory adjus tment, tightly coiled, inact ivosidew inders (anel C . nutchelli pyrrlws) w ere ablc to conse rve heatmore effe ct ive ly th an uncoil ed snakes. Often, ten or more C. cerastesma y be encounte re d by clriving ronds at night in áreas where theyare com mon, with as many as 30 occasionall y b eing seen. Peak ac­tivity appe ars to be lat e May and early [une, partícularly in th ehours just af te r sun down. Siclewinders will often coil on asphaltroads whe re au tomob iles ca use hea vy mortality. Brown (1971) feltthat the sna kes us ed roads as a source for irradiated heat.

Sidewinders are ra the r pug nac íous and will strike readily. Theywill often turn an d bite when restrained, a ch aracte ristic u suallyassoc ia tcd wi th monta ne fo nn s (C. icillardi, C. poltjstictus ), Theyprefer a di et of l ízards (Unta, Dipsosaurus, Cnemulophorus, Uta,Crotaplujtu s} in cap tiv íty , and cap t íve sidew índcrs will often refusem ice, Im t rca dí ly consu me an iguanid lizard . \Ve observed a captíveadult fem al e C. C. cercobombus feeding on three of h er newbornyou ng.

The vc ge ta tíonal reg imes inhabited b y this species include theSeasona l F onnation Series an d C actus Scrub as defined b y \Vagner(1964). Low e (1964) dcscríbed th e habítat of this snake in Arizona,

Crotalus duri ssus L ínnaeus

The Neo trop ica l rattlesuakes, C. durissus, are among th e largestand some times most aggres sive rattlcsn akes indigenous to Mexico.\ Vith the excep tion of an isolated subspecíes, C. d. iotonacus Foundin Trunaulipas, Qu er étaro, Veracruz, and sou the rn San Luis Potosí ,snake s of th e C. durissus comp lex a re inhab ítants of thc countrysou th an d east of th e Xlexican Plnteuu, including th e entire Yucat ánpeninsula. Despíte th e fact th at th e comm on nam e given C. durissussuggests a ju ngle in hab itant, thesc ra ttles nake s rarel y will be foundin such moi st plac es, much pref erring savannahs or part íally woodedhi llsides ,

C rotalus durissus durissus . Crotalus d. tlurissus is a rcsiclent ofthe Xlexica n sta tes of T abasco, Ch iapas, central Veracruz, aneIsou theas te rn Oaxac a (Klaub er 197:2). Klauber (1952: 65) cite cl difler­ences in snakes fr om near Jalapa a ncl Orizaba, Veracruz, and sug­gestec1 tha t w ith examination of mor c specimens this populationmay meri t subspecific recognition. C rotalus d. tlurissus has beenrecorded by us from th e Follo wing localities: CHIAPAS: 12.8 to]8 km l\E Tapana tepec, OAXAC A: 19.3 km W Tehuantepec.

Th ís rattlcsnake prefers d ry sav annah habitats with Frequentrock outc rops. H artweg and Olive r (1940) characte rízed th e hahitat

12 SPEC IAL PUBLICATI ON- r-.m SEUM OF NATURAL HISTORY

FiG. 5. Habi tat of Crotalus duri ssus culm inatus, near [ojutla, Mor elos ,Mexíco. Opcn tropica l deciduous thom forest characteri zed by limestoneoutcrops. (Pho tograph by M, Gra nger.)

this rattlesnake a voidcd lowl and situations , snakes from Copala,Guerrero , and La Placita, Michoac án, have Leen recorded fromnear sea level, Th is lowl and habitat can be descríbed as aridtropical scrub fores t, characte rize d by Irequent rock outcroppings.Davis and Smi th (1953 : 141) found C. d . culniinatus common inlowland mo untains south of Tepaltzingo, Morclos, on the northernslopes of the Hío Bal sas basin . This urea is al so interlaced withextens ive limestone ou tc ropp íngs . Duellman (1961: 121) commentedthat 18 specimens from E l Sab ino, Michoac án, wcr e found near theupper limi ts of th e arid scrub fores t (1050 111) on th e lower slopesof the Cordi llera Volcánica. A spe cime n from near Morelia,Mi chonc án, the northern limit of th e range of C. d. culminatus,was taken on the edge of a lav a flow at 1982 m in a mesquite grass­land habitat with isolated sta nds of scrubby oaks. Throughoutmuch of its rango, this subs pecies is gc nc rallv nocturnal , and seemsto reach a peak period of ac tivi ty duriug th e su mmer rainy season,as do mo st Mexican Cro talus . A capt íve pair was observed copu­lating on 4 Februarv 1978 .

Cro talus d . cull/l!nalus inha hits the Aricl Tropical Scrub Forest(D ueIlman 1965) and th e T em perare Pine-Oak Forest as definecl byLeop old (1950).

C rota lus durissus totonacus . The northeastern subspecies, C. d.totouacus, is probably the leasl stu d icd Fonn of C. durissus. Sinceits descri p tion in 1940 (Cloyd a nd Kauffelcl), Iew specimens havo

TlIE NATUR.AL HISTOR Y OF 1IEXICAN RATTLES NAKES 11

of thi s sna ke in the vic ínity of T eh uantepec as plai ns. Klauber(1972: 531) suggeste d that th e habitat of G. d . d urissu s was sorne­what like th at of th e arid sou thwcs tern United States. Sp ecimcn sob taincd b y us from extre m e southeas tcrn Oaxaca and sou thwest­em Chia pas w ere fou nd to b e ve ry co rnmon in rocky, grassy situa­tion s wh ere forest s had been partially cIea red . In late Jun e, threew eeks after th c rainy scason had b cgun, ind íviduals w ere foundat n ight on the road between Tapan atepec and Rizo de Oro. x lostwere obscrved on evenings when rains w ere in th e fonn of lightd rizzle. Crotalus d . tlurissus rangos from ncar sca lcvel to at lcast1585 m ncar Co m itá n, Chiapas (Klauber 1972) and is found in th eTropical Hain Forcst as defincd by Wagncr (1964). According toGoldm an (1951), th e w ild gourd trce, various cacti , Ca ssia , Acacia[arnesiana, Prosopis ;uliflora, two sp ec íes of [atropha , Annona, two0 1' m ore species of Ficus, l pomoea, two species of Pithe coll ohium ,fan p alms and the gu ásíma (Cuozuma ul m ijolia} ar e found in th ear ca inhabited by thi s snakc.

On 8 D ecernber 1976, \ V. E. Lamoreaux (pcrs. comrn.) introduecdan adu lt malc G. d. CUII l(l/wnsis in to an cnc!osure (100 X 80 X 75 cmhi gh) co u ta ining an aduIt Iern alc G. d . du rissu s. The m aIc initiate dhead-bobbing movem ent s wi th ra pid tongu e-Hicking ove r th e fe­malc' s dorsum , T he fem ale rem ained passive und 110 intromissionwas ob servcd. The nex t day, th c p air was in copulo at 1300 hours.The coital p ositi on of thc p air was unusu al for alth ou gh the snak eswere finn ly joined by the hcmi penis, th e tails w ere pointing indirectl y oppos ite p la nes. The ma le's bod y pu lsat ed near th e ve ntand th e tai! was curled upward. During intromission, th e maleopen ed hí s mouth intermitteutly and b egan a se ries of vertic al headand neck jerks with occasional tonguc llicki ng. Parturiti on occurredon 10 June 1977, and prod uccd on e dcad a nd ninc viable neona tes.

Crotalus durissu s culminatus. Crotalus d. culm inotus, a PucificCoas t ra ee, ra nges From uear sea lcvcl ncar La Placita , Mi chonc ún,and Copala, Gucrr ero (Wayne Seifert, pers. comm.), to 1982 m nearXloreli a , Mich oac án. T hcse ra ttlesnakes may reach ele va tions uear2285 m in th e Sierra d e Coalcorn án whcre we have seen tannedskins , Local rcsid euts h ave ídentified live individuals, but thisid cntification should remain tcntative until mo re reliable data ar esecured. This subspecí es occurs from near th e Colima border atL a Pl acita, M ichoac án , north ea st to Morclia , east through sou the rnMor elo s and w este rn Pue bla to ext re me sou thweste rn Oaxaca , in­cIuding th c cnt ire sta tc of Guerrero. Specimens have b een recordedb y us from: ~IICHOACAN: ncar La Placi ta , 7 km W Morel ia(J. A. Campbell, p ers . com m.), Morel ia : ~IOHELOS : 5 km WJojutla.

Grata/lis d. cuhni natus is an inhabitant of rou gh, rocky, generallyarid hab itats (F ig. 5). Although Klaub er (1972: 530) th ought th at

TH E NATURA L HISTOR Y OF MEXICAN RATTLESNAKES 13

reach ed collections, an d onlv recent lv, with th e con structi on ofnew roads , has C. d. totonacus hecn ol;served with some frequencyby field in vest igators. Record s obtained by us are fro m TA~ I AULI­

PAS: 48 km N Soto la Marina, 16 km N Aldama. F our su badu ltind ivíduals w ere found ki lled on the road in Tamaulipas: E l Carrizoat Kil ometer Post 26 on 2 Ma rch 1977 (1-:U 17482.5),20.8 km N Sotola Ma rina on 29 April 1977 (1-: U 174826 ),38.4 km N Sot o la Marinaon 29 April 1977 (KU 174827), 33 .6 km N Sot o la Mari na (1-: U174828). To pograph ícal sim ilarities suggest that C. d. tot onacusmay be found in the sta te of Hidalgo.

Líkc most raees of C. du rissus, C. d . totonacus is typicall y alowland inha hi ta n t, a lthough sp ecimens ha ve been reported from1680 m in th e lower cloud for est of the Sierra de G uatemala (M a rt ín19.58). Throu ghout most of its run gc, th e arca s inhabitcd b y thi ssnake are ei the r tropical thorn or tropical deciduous fores ts markcdby di stinct w ct -dry seasons . Two sp ccimen s (b oth juven iles) fromeas t-cc ntra l T amaulipas, co llected by [ oh n E. Jo)' (pers. com rn .) on7 and 8 Au gust 1975, wcre found ac tive shortly a íte r dark d uringrain showers (F ig. 6). A juvenil e (UTA R-6707) Iound k íllcd on th croad at Kilomcter Post 17 ncar La Xlari na Viejo on 2 March 1977co ntaine d rodent h air. Crotalus el. totonacus appcars to pref er arcasaround any type of wat ercou rsc , Loca l rcsid cnts ass ure d us th atthis is wherc most of these rattlesnakes wcre seen, hut D ixon el al.(1972) found this su bs pecies in eas te rn Q uerétaro at 1.585 m in a

,/'

FI(~ . 6. Suba du]t Grata/lis durissu s totona cu s. Specimen from 48 km NSoto la Marina, T amaulipas, :\Iexico. ( Photograph by j onathan A. C ampbel l.)

14 SPEC IAL PUBLICATION-~IUSEUM OF NATURAL HISTORY

pine-oak for est near no stand ing w ate r. P. Pritchard (pe rs . comm.)Iound a largo individ ual on th e b ank of a small dam. These rattle­sna kes are co mmon, but as is th e case of mo st forms of C . durissus ,th e p eak p eriod of ac tivity seems to be limited to the rainy season .Growth rutes of cap tive young are th e mo st rapid of any rattlesnaketaxa maintai ne d bv uso

C. d. ( 0( 0 /10 CU; inhabí ts the T rop ical Thorn and Tropical D e­ciduo us F ores ts, som e elements of th e ternperate dcciduou s fores tas deíi ned by Leo po ld (1950), and th e Seasonal F ormati on Seriesand Steppe, Thicket an d Scrub D escrt as defined b y Wagn er (1964).The arca suppo rts mesquite, huisach e, ebony a nd other shru bs,Along th e str ca ms , b ald cy pre sses (Toxod ium} and cottonwoodsare corn rn on (Goldman 1951).

L. A. Mitch ell an d J. E. [oy (pers. comm.) discovercd a mal eC. d. totonacus measu ring 1.7 m total length, in combat with annd ult ocelot, Felis pardalis, during February 1977. The animalswere bclow a thick canopy of th orn scru b in early aftcrnoon andth e ground b eneath th e canopy support ed little vegetation. A dis ­tance of 1.3 m se parated th e combatants, and th e snake w as in adefensivo p osture typical of C. durissus, and rattling vigorous ly.T he ocelot rem ained immobile with th e rig ht forcleg ra ísed . Whenthe snake w as exte nded fuIl)' w ith it s mouth open af te r a strike,th e ocelot raked wi th it s claws w ithin th e snake's mo uth, th enwi thdrew th e paw b efo re th e suake could close it s mou th . Latcrexamina tion of th e oral cavitv al1CI th roat of th e sna ke rcvea led anumber of lacerations in the so ft tissue and masse tcr mu scles wh ichwe re intl ict ed b y the ocelot , b ut the interstitial skin and scales ex­terior to th e laceration s w crc 1I0t aíl'ecte d. L acerat ions werc fou ndon th e dorsa l aspe ct of th e head and ueck, but not near th e pu nc­tures withi u th e suakc's mouth or throat . The snakc's 10\Ver jawwas out of alignmen t and the mandib ula r bo ne w as visib le whenthe mou th wa s open. A largo female C . d. iotonacus wa s locat ed15 mi nu tes late r, wí thi n 12 m of th e male. The ma le ra ttlesnakewas treated for its injuri es, but succumbed abou t tw o w ee ks later(1-.: U 174824). Th e snake regurgi tated a large numbcr of ascaridsd uring the two w eeks prior to its death.

CrotaIus durissus tzabean. The Yucatún ra ce of th is sp ccies,C. d . tza bca n, unlike C. d . durissu s and C . d. culnü natus, is stric tlya Iowland inhabitan t from th e Yuca t ún pcninsul a , and ran ges fr omeastc rn Tabasco to inelude all of Campeche , Q uint an a Hao, amiYucat án. Nei ll and AIIen (1959, HJ60) reported on this ra ttlesnakcin British Honduras.

Crotalus d . t zabcan is q ui te co rn mon throughout th e Yuca t ánpeninsul a. Ducl lman (196.5: 611) descr íbed its habitat as scru bforest w ith numerous lim eston e ou tcrops . Four sp ecimen s ob taine dby us \Vere found bet\Veen Kantunil and C hichén llzá, Yueatán ,

TIIE NATU RAL HISTOHY OF :-' IEXICA:\ RATTLES:\AKES 15

a íte r 1600 hours (UTA H-5659-60), fo llowing a two-h ou r rainshower,

A male, taken on 18 September 1974 betwee n Kantun il andChich ón Itz á, Yucat áu, and a fem al e obtained on 29 August 1969at Uxmul, Yucat án, were placed togcth er on 11 O ctob er 1974. TheFollowing observations w cre recorded b y T err y H uls ev (pe rs.comm.). The female exhibi ted nervousn ess an d refused to coil nea rth e mal e. O n 24 Oct ob er she was placed in isola tion an d againintroduced on 7 No vemb er, The mal e shed on 29 D ecemb er andth e fem al e was co ile d nex t to th e mal e for th e firs t time since th eywere introduced, Courtship beh avior was seen on 30 December.The mal e b egan rapid head-bobbi ng a neI tongu e-Hicking. H e ap­proached th e female and tapped her do rsum repeatcd ly in th evicinity of th e 13th a nd Ióth scalc rows . The male' s activity Iastedca . 30 seconds a ud he rem a ined immob ile for ca. 30 seconds, At th eend of eac h period of acti vity, th e ma lc's tail eucirclcd thc femalein th e vicin ity of th e ven t and h e jerked violently. C eu crally. th ehead-bobbing motions w ere d irect cd antcriorly . Pre-coita l activi tywas continued afte r th e mal e di scontinued th e cloacal scarchingmoti on . The sna ke s did no t cop ulare. 011 2 January lm.5 th e cagewas sprnyed w ith w at er a t OS30 hou rx an d th e male b egan tw itch ingshortly th ereafter. The snakes wcre found in copulo a t 1.500 hoursand th e ma le slowly moved hi s tail in a lat erall v c1 irect ed twitchiu gmot ion, The fe male was wcighcd pe riod icall y after co pula t iou anelth e wei ght incr ease was as Io llows : 2,1 F cbruary 1975 (2.1 kg); 20Ap ril (2.6 kg ). 12 ~J ay (2.7 kg): 2.5 [ ul y (3.0 kg). Twenty-on e youn g(two dead. l( lj 158547-8) wcrc bOJ"l1 0 11 3 1 Au gu st ami wcre imm edi­a telv we ighed and mcasurcd, T IJ e ran gc of va riation is as follows:to ta l len gth 290 -3.50 mm . mean 316: ,, 'e ight 18.4-26.S g. mean 23.'1.Othcr pa rturition d ates are 3 1 Au gu st lm.s (LT T.\ H-67:32. GS02). 2August 1976 (UT A H-67.'3.3) aud 3 Augu st (UT A H-6734 -3.5). Figur e7 re prcscnts on e of th e young at 35 inonths.

Crotalus d. tza bcan is Iound in th e Tropical Eve rgree n andTropical Hai u Fores t as defiu cd b ~' Lcopold (19.50). Th c a rca xup­ports Entcrolobt nm cijclocarinnn , two or more specics of Fi cus,Spanis h ccdur, Iogwood. two spc cics of silk -cotton, th e chico znpo te(Ac!lras zapoia}, p alo m ula to (Bu rscra}, two or more species ofCassia, g ian t nettle (Urera caracasaua} ancI Agave (C old muu 19.51).

'rhe subspecies of C . dllrissus are vcry llnp redict able ill telll ­pe ra lllen t. At times th ey are aggressi\"(' aneI stand th ei r grouJl(I,wh ereas at other times th ey are pla cido O ur specime ns h a\'(~ ex­hibited both of th ese b ehaviora l ext re mes. ~ Jost C. dllrisslIs ar e atIcas t part ially no ctum a \, anel al! sce lll to reach peak ac tivi ty duringth e Slllllmer rai uy season. Young of thi s species h,1\"e been co llectedfrolll late Jnne throu gh late August.

16 SPECIAL PUBLICATION-:VWSEUM OF NAT URAL lIISTORY

'jl

·1

..'r

i rI .

I r'FIG. 7. Cratalus d urissus tza bca n. Sec texto ( Photograph by [ onathan A.

Campbell. )

Crotalus C Il !JO (Cope)

C rotal us C Il !JO. tho ugh w ídesprcad throughout Baja Ca lifo rnia ,rerna ins bi ological ly ncgl cct cd in literatur c on ra ttlcsnakcs (Klaubcr1931). It is characte rized by an unusually small h ead and rathcrlarge ra ttles , also tra its of C. tigris, a sp. -cies not Iound in Ba jaCaliforn ia . Haces of C . C Il !JO are moderately sized rattlesnakes, andthroughou t much of th e ra nge, are lowlaud or mountain desertdwell er s. Van De nburgh and Slcv in (1921) found this rattl esnakearound human habita tions,

Crota lus en yo eny o. The subspec íes C. C. e ll !Jo is a rnther com­mo n ra ttles ua kc in th e C ape region of Baja Ca lifornia del Sur (F ig.8). Specimens a re kn own from E l M ármol , Baja Califo rn ia delNo rte, sou th through out th e pen ínsul a to th e south cr nm ost point.Specimens obtainc d b y liS wer e collec tc d at San Antonio (64 km SLa Paz) and 14.4 km N Buen a Vista (B. Tomberlin, pcrs . comm.).

Crota lus c. C Il !JO is an inhabi tunt of arid, ru gg cd deserts anddesert mou ntains th rou gh ou t its range. Kla ubcr (1972: 531) sug­gest ed that snakes Io und fro m La Paz to San José del Cabo werefrom an ari d region co ntai ning a profusi ón of cacti , xerophyticshrubs, and rocks. In centra l Baja C alifo rnia, th is ratt lesn akc Iivesin association with la rge bould er s, th e gíant ca rdo n cactus (Ccreuspringjei), th e boojum (l dría), and th e Ion g-li ved elophant trce. B.Tornb erlin (p crs. com m.) comme nted that, in th e arca sou th of LaPaz, thi s subsp ecies liv es sympa trically w ith c. rub er lucasensis

18 SI'ECIAL PUBLICATION-~IUSEm l OF NAT URAL llISTORY

California, C. e . [ur ous was known from Iew spccime ns , no doubtdu e to the previous ly poor road condi tions whieh preventcd aeeessto the op t íma l habitat of th is snake .

The San Quint ín Plain is characteris tic of coasta l, ope n, low­growing scrub habitat s in Baja Californ ia del Norte . Klau ber (1972:531) descríbcd the area as muc h like we ste rn San Di ego Co unty ,Californ ia , bu t somewhat more rocky and with a Iighter brushcover. Lowe and Norris (19.'54: .57) char ac te rized th e area as co n­taining a markcdly more mesic clima te and biota th an th e harsheuviro nmcnts both southward and in th e inter ior of th e pen ínsul a .The av erage annual rainfall is abo ut 1:2.7 cm (Beal 1948), and coastalfog produces some add itional mo isture in th e ar ca . On e specimen ,obtai ncd b y us nea r E l Socorro, appc ared to come Irom a sandyhill wh er e vegetat ion was sparse, and th er e w as a profusi ón ofcoastal ground cove r. Xlnny bu rro ws we re noted. A specimc n col­lccted b y R. T. Basey in Octob er 1972 (ambient temperature 21°C)carne From a light-color ed mud wash wherc vegetation was ex­tr em ely spa rse (pers. connn.). This specime n was a young adultIerna lc which lat cr gave birth to sevcn youug on :26 Augu st 1974.To tal len gth of th e you ng wa s fro m :206-2:2:2 mm, mean :213. D ennisBostí c (pcrs, comm.) rc la tecl tha t h is scven specime ns of C. e. [ur cu sfrom nea r Pun ta Camalú were collccted wh cr e two alluv ial fa nsmet. Eight additional snakes were taken by ouc of us (BLA) be­tw ecn 10-15 October 1977 in the vic ínity of E l Rosario .

Crota lus e. [urous appcars to be a t least partially no cturnal inthat two individuals recorded by H. 1', Basey and T. Portcr (pe rs.eomm.) wer e collec tcd on a road at night. The typ e specimen ofthis race was taken at noon in the mouth of a small rod ent burrow,The Scascnal Formation Seri es as defincd b y W agn er (1964) istypica l of arcas inhabited by C. e. [ur cu s.

Crotalus inter medius Troschel

Thc sma llhead ra ttlesnakes. C. int crmedius, of southe rn M éxicorem aín hiologica lly amoug thc least und er sto od specics of rattle­snakcs, Li tt le published material on these snakes is available, andFew spec imcns are avai lable in mu seum co llectíons , Most exa mp lesof th is rattlesnake a re Frorn southcastc rn Mexico, but Ducllman's(1961: 121) record of an individua l from Ce rro Tanc ítaro , Michoac án,is indeed uuusual. \Vhcn more ficld work is done in ar ca s bctwecnknown localities, th c taxonom íc status and geog raphic va riationwithin C. inter mcdius shou ld hecom e more appar ent.

Cro ta lus in te rme dius intermedius. Crotalus i. int ermcdius hasbeen rccorde d from castern H idalgo, wes t central Vera cruz, andnorthcastern Puebla (Klaube r 1972 : 39-40 ). Pianka and Smith(19;'59) found C. i. inter tnedius 16-24 km W ]apala, Verac ruz. Asingle speeimen (KU 155530; F ig. 9) from near Cacaloapan, Pu ebla,

TH E NATURAL HISTOR Y OF MEXICAN RATTLES NAKES 17

"

. , ..... . . " .' .

# ..... . . ..

F IG. 8. Grata/lis cuyo cuyo. Sp ecim en from ·14..t km r\ Buena Vista , BajaCalífornia del Sur, Mexico. ( Pho tograph by John II . T ashji an . )

and, to a lesser degree, wi tli the spe cklcd rat tlcsnake, C. 111. m itclicll í.He also sta ted th at spccimen s 01' C. C. C Il Y O are found in that a reafrom arid llat descr t p lains to rocky dcscrt mo untai ns.

Cr otalus e. ell Yo is nocturnal f01' a goo d portion 01' th e year, nndseems to rcuch a peak activi ty pcri od in the ea rly fa ll wh en southe rnBaja California receiv es a fair am ouut 01' its an uual rainfall. Atth is time it is cornmonly Iound crossing roads at night.

Ca p tive reproduction in C. c. eruto has been rep orterl (T rvonand Rad cli ffe 1977). On 15 j anua ry 1975 cou rtship activity runougsnakes mai ntai nc d bv us wa s ob servcd het wcen 1530-1700 hour s,The fem ale had just ~hed and the mal e rubbc d h is mental a rca onth e Iema lc's dorsu m with co nvu lsive Iorward jerks in th e ma nuerof C. ioillardi silus (describe d la ter in th is pap cr) . During this pe­riod the ma le tr ied vigorously to thrust his tail hen eath the cloa ca]region 01' the female, an d in sorne ins tances, th e malc's tail co rn­plet ely eucircl ed th e Iemale's clo aca . T he mal e would slide Iorward1-2 cm b y extc nding h is looscly draped coils and bracing his bodyat th e cloacal region of th e female . Lo", int ensity twitch es accorn ­panied th is beh avior . Co pnlation wa s not observed,

Crotalus e. ellYo is an inh ab itant of th e Sensorial FormatíonSeri es as defined by W agn cr (1964).

Crotalus en yo furvus. Thc Rosario ra tt lesnake, C. e. [ur ous, isa northern fonn of th is species from the San Quintín Plain 01' th cwest coast 01' Baja Californ ia del Norte (Lowe and No rris 1954).Until recently, with the complet ion of a paved road throu gh Baja

TIIE NATURA L HISTO RY OF ~IEXICAN RATTLESNAKES 19

ca p turcd in th e su mmer of 1974 by one of us (BLA), extends th erauge of this fonn some 160 km (airline) to th e sou th . This ar ea isat an elevation of 2195 m and is dominated by high desert vegeta­tion where cacti , agave, and yucca ar e prevalent. A rattlcsnake ofthis mee ob tained by us was tak en at 099.') hours wh en sunligh twas d ilTused and humidity wa s high . It was basking in partial shadeun der a 1arge agave on a southe rn facing hill. Thunder storms oc­curred the previous evening, but th e porous limestone soil surround­ing th e coIlecting site showed Iittl e evide nce of moisture. Thevegeta tional h ábitat preference of c. i. interm edius incIudes th eT ropical Evergree n Forest as defined by Leopold (1950).

Crotalus intermedius gloydi. A Oaxacan subspecies, C . inter­mcdius gloydi (Fig, 10), is a montan o race from th e mounta ins sur­roun di ng th e eity of Oaxaca. 1'0 ou r knowledge it has not beentak en from th e desert ar eas of that region . In th at respect , itdillers grcatly from th e nomina te northern subs pe cies. Three suakesobtained b y us have come Irom th e humid pin e-oak forests abo ye2440 m (F ig. 11) an d another spe cimc n (KV 155529) from no rth ofIxtl án de ju árez at 3020 m. This 1atter indi vidual was found on awcs t-Facing slope th e day foIlowing a violent hail storm wh ich leftab out 5 cm of hai! on the ground . The da y it w as eapturecI , how­ever, was hot (27°C) and sunny, The sna kc w as fou nd in th e shadeof an oak that had begun to sprout new foliage afte r being b urnedin a Ei re . J. R. D ixon (pers. comm.) found a specime n of C. i. gloydi

e

FIG. 9. Crotalu s int ermcdiu s intcrmediu s. Specimen from Cacaloapan,Puebl a, Mexico. ( Photograph by John 1I. Tash jian. )

20 SPECIAL PUBLICATION-~IUSEUMOF NATU RAL HI STORY

cra wling up a vertical ston e wa ll at night in a rainsto rm along ahighway cut 57.2 km N Oaxaca at 2286 m on 6 [une 1956. Otherspccimc ns of C. i. gloydi collcc tcd by us carne fram near E l Tcjocotc(UTA R-4915 , 5627 , 5637, 7163), which is northwest of Oaxaca, Thisar ca has bc en extens ívely log ge d, an d only sca tte red arcas supportrattl esnake populations, Six additional specirnens were collectedin July 1975 from near Cerro Ma ch ín (Sierra de [u árez), Suchixtepcc(Sierra ele \ liahuatlán) and El Tejocote (Sierr a de Cuatra Vena dos).Other snakes from th e vicinity of El Tejocote are as follows: (UTAR-4915) coll ected on 20 August 1975, (UTA R-5627) during Aug ust1975 from a pine-oak, madro ño for est at 2440 m, (UTA R-5637) dur­ing Augu st 1975 in a pine-oak for est at 2285 m, (UTA R-5791-2)on 17 June 1976 in a pi nc-cak forest at 2285 m, (UTA R-6062-63)on 31 Jul y 1976 in a p íne-oak for est at 2285 m, (UTA R-6122) cluring[uly 1976 in a pin c-oak for est at 2285 m, (UTA 1\-6229) clur ingAugust 1976 in a pin e-oak for est at 2285 m an d (UTA 1\-6356) dur­ing June 1975. \Ve have obs orved ri tualized com bat between maleC. i. gloUdi shortly after capture .

The Montano Formation Series anel Mont ano Thicket as definedby Wagner (1964) is cha racterist ic of the habitat of C. i. gloUdi,and Ducl lman (1965) list ed it as a resident of Pine-O ak Forest .Blue-Ilowered Solanuni , Ceanotlius COCru IC lI s, wild chcrry, and two01' more spccies of oak s and pines are found in th e area (Goldman1951).

Cr otalus intennedius omiltemanus. A Guerre ran subspecies,C. i. omiltemanus (Figs. 12, 13) is prob abl y the most thoraughlystudied raco of th e smallhea d ra ttl esnakes. Most cxamples of thi ssuake llave been taken in th e huinid pinc-oak for ests (Pilllls herrerai,P. pseudostrobus, Qu ercus sp .) whích su rrouu d Omiltem e in th eSierra Madre del Sur (Davis and D ixon 1957, 1959). Nearly allspecimens (35) ob ta íned by us were collected within pine-oak for est(UTA R-4707-10, 6232-33, 6245, 6821); only one individual , collectedOll 25 Mav 1975 fram 3.2 km \ V Omilteme, was taken in an areaof secondary growth in the adjacent hardwood cloud for est at2653 m by J. A. Campbell (UTA R-5626). This latter snake may hav creached this area via a power line cu t. These rattl esnakes also werefound only during th e major rainy scason which usually began in\ lay. This ar ea may receive precipita tiou cve ry month, but from[ anu ar y to Ma y, it is rather dry. C. i. omi ltemanus is appa rentIya rock-d weller , and none of th e specimcns ob tained by us wa sfound any distance from a rocky ret reat , with th e cxcep tion of th ecloud Iorest specime n. 111 most instances th ey we re found baskin g0 11 racks, espe cially after a rain. One snake (UTA 1\-2813) wa s founddea d on a grassy hillside on 19 May 1973; cause of dcath was notde te rm ined. \Ve coIlec ted snakes fram 2075-2592 m, and doubttha t th ese rattl esnakes are found near Chílpancin go which has an

TH E NATU RAL HI STORY OF !,,[EXICAN RATTLESNAKES 21

FIG. 10. Crotalus iut erm edius glor;d i. Specimen fra m 31.3 km 0: Ixtl ánde Juar ez, Oaxaca, Mexíco. ( Pho lograph by John H. T ashjian . )

FIG. 11. Habitat of Croialus int erm edius glor;d i, pine-oak forest 31.1 km NIxt l án de [uarez, Oaxaca, Mexícn , july 1975. Area had becn partially cutand burned th e pr evious year, characterized by epiphy tic pl ants. (Photographby Jonathan A. Campbell.)

22 SPECIAL PUBLICATION-}, IUSEU},I OF NATU RAL HISTORY

elevation of 1372 m (Klaubcr 1972: 533). Althou gh C. i. omi ltema nushas been definitely rccorded only from th e vici nity of Omiltemc,it was to be expeete d th at with addi tional field eolleeting othe rspeeimens would be sec ure d throughou t th e llpp er reach es of th eSierra Madre del Sur. Supportive evidenee of this sta temen t is in­di eat ed b y th e eolleetion of a specime n (UT A R-5638) on 28 May1975 from 1.6 km SW Filo de Caballo by J. A. Campbell, Anotheradult snake , observed approximate ly 1 km N Puerto del Gallo (some60 km WSW Omil teme), escaped befare being ca ptured. T he ele­va tion a t thi s site was 2950 m, and an example of Bothrops barbou riwas d ísco vered nearby. Melan ísti c speeimens of C. i, omilteman uswcre eolleeted in San Vincentc, Guerrero (UTA R-4538-9). Fivenewborn YOllng of this mee were Iound 1.6 km S Orn ilteme in p ine­oak Forcst at 2286 m on 28 May 1975. Range of va ria tion for lengthand weight is as Follows: total lengt h 194-212 mm, mean 205;snout-vc nt 182-195 mm , mean 190; weig h t 4.9-5.4 g, mean 5.2.Ritualizcd eombat between adu lt males was ob servcd by llS amongfour recent ly eaptured snakes .

Cump be ll (1977) exam inc d th e stomuchs of 18 C . i. om iltemanusIrom Omiltem e, und revealed that these snakes fed almost exclu­sive ly on lizards (ge nus Scelcporuss wher eas th e stomaehs of ]5exumplcs of Both rops undulatus from the same arca con tainedmo stl y rodc nt remains,

Crotal us lepidus (Ke nní cott)

The rock ra tt lesna kes , C. lepidus, are typ ieal examples of thevarious smal l mon ta no, rack dwel ling ra ttlesnakes inhabiting M éxico.AII Iour subspecíes, Icpidus, kluub eri, IIU1CllloSlIS , and //1 orulus, ar egencra lly ti m íd , ye t rather irritabl e and eurious a t tim es. Through­ou t much of the range of C. lepidus in Mexico , on ly limi ted numbersof specime ns have been reeorded, probably bccau se th e terraininhab ited by th ese snakes is gcu erall y steep, ru gged , an d inacces­sible. More specimens a re nee ded from th e southe rn Iimits of theranges to cla rify th e relationsh ip bctween C. lepulus und C. tri­seriatus (G loyd 1940 : 81).

Crotalus lep idus lepidus, The nomina re mee, Crotalus l. lepidus,is foun d in pinc-oak for ests through mu ch of its range, though dcsertpo pula tions are not uu cornmou. This snake rangos from southeas t­ern ~ew Xlcxico and T ran s-Pecos T exas , south th rou gh Coahui la ,wes t-central Nue vo León , eas te rn Zaea teeas, and no rthwest ern SanLuis Potosí (Klauber 1972: 62).

C loyd and Smi th (1942: 235) re porte d a sp ccimen of C . l. lepidusfrom thc Sierra del Carmen at 1830 m on an open, sou thwes tc rnIacing slope where junipe rs were present. T uylor (19.52) reporteda sn ake from Cerro Pe ñon Blan co, San Luis Potosí at 2928 m. Thesingle specimen of th is ra tt lesnake, ob taine d b y us from La As-

THE NATU RAL HISTORY O F MEXICAN RATTLES NAKES 23

F IG. 12. Crotalu s intermediu s ami ltem anu s. Melanistic spec ime n fromSan Vicente, Guerrero, Mexíco , ( Photograph by j oh n H . Tashiian. )

F IG. 13 . C rotalus intennedius omiltemanus. Specirnen Irom near Omilteme,Gue rrero, Mexico. ( Photograph by [ohn H. Tashjian . )

2--1 SPECIA L PUBLICATIO~-~IUSEU ~I OF ~ATURAL HISTORY

ce nsi ón, Nue vo León , was found under similar conditions at 2075m wh ere junipers, pines, and agaves wer e pr eval ent. The specime n,a gravid femal e weighing 44 g and me as uriug 435 mm total length(400 mm S-V), appeared to b e assig na ble to e. l. morulus accord ingto Klauber (1972 : 130) b y its having 28 crossbands , However , threeof th e six young born to thi s Iemale on 5 [une 1974 had Icwer th an25 cross bands , ami three had 25 0 1' more (one mal e had 31 cross­bands). Range of varia tio n for length and weight for this broodis as foIlows : to ta l length 165-190 mm , mean 177; S-V 150-173 mm ,mean 162; weigh t 5.0-5.7 g , mean 5.2.

Mil st ea d , Mech a m, an d ~ l eC l i n tock (1950) found e. l . Icpidusin a persimmon, sh in-oa k associa t ion, and th e Scrub D esert as de­fiued by Wagner (1964) is its cha rac terist ic h ábit at . Mintou (1959)deseribecl the hab itat of thi s m ee in th e Trans-Pecos area ,

C ro taIus lepidus klauberi. Crotalus l. klaubcri is norm ally aresident of moderate elevations in foreste cl mountain s thraughoutmo st of its ra nge. Sna kes from extreme west T exas in th e FranklinMou nt ai ns are an excep tion since th is mountain ran ge is ve ry aridwith lit tl e veg etat ion. Spcci mcns ob ta ine d b y us are from : C H I­H UAH UA : 16 km S Chihua hua. Arrovo Xlest efi o am i Cañon delAlam o in th e Sierra del Nido, ne ar \ 'ilí a Matam oro s: DUHA~GO:near Villa Oca mpo.

Most of th e data on e. l. klaubcri obta ine d by us have beenfrom exa mp les coIl ected in the C hirica hua a nd Huachucn Mountain sof sou theastc rn Ari zon a , \ Vitlt the exce p tíon of th e snakes fromth e Sierra del Nido , Chihuahua, spccime ns ob ta inecl by us fromMexico were coIlec te d on roads, and a Il carne from ge ne ra lIy th esa nie typ e of ter rain, p rima rily desert canyo us with rack ou tcropsor ledges, a nd sparse vegetation . e. l. klauher¡ was collecte d atclevations fro m 915 m south of C hihuahua to 1372 m in the vicin ityof Villa O campo, Dura ngo, w here grasses a nd oa ks fonn a sava nnahenvironmcnt. In the Chirica hua, Huachu ca , aud Sierra del N idoMo untai ns, e. l. klau bcri is oft en located along rocky strea m bcds,aud during the summer rain y sc ason is obse rved in open pinc-oakfores ts. T hese rattlesnakes are mostlv d iurnal , a t least in forest edmo u nta ins , and are most eas ilv obscr~'ed on w arm , humicl summe rdays wh en th ey reveal their prescnce b y rattIi ng . Hitu ali zed combarbetwccn males of this su bspecies has been obs erved (C arpente r el al.1976). A fema le specime u, coIlec ted at II erb Xlurtyr Dain in th eChiricahun Mountains. Ar izona, gave bi rth to three young on 28August 1968. Fo ur young were born on 30 Augus t 1975 to anothcrfemale spccimen coIlecte cl 4.8 km S Mad er a, Chihuah ua , and ran geof variation for length an d weigh t is as Io llows: tot al len gth 181­196 m111, mean 191; S-V 164-177 m m, mea n 172; weigh t 6.3-7,0 g ,mean 6.6. A captive pair of e. l. klauheri \Vas observed to br eedon 21 Febmary 1977. H. K. Guese (pers. eoml11.) ob served a eaptive

TIIE NAT URAL HISTORY OF ~IEXICAN RATT LES ;"¡AKES 25

pair of this race from th e Sierra dcl Nido, Ch ihuah ua, engaged incourtship activity on threc occasions between 14-28 Septemb cr 1977.The male directed rapid head-bobs (3-5/5 sec) on th e dorsum ofthe female. Tongue-flicking occurred at th e same speed. Thesnakcs were disturbed afte r 5 minutes anel discontinu ed the be­havior. Another pair of th esc snakes was ob served courting on 11Octobcr 1977, and th e male exh ib ite d the same head-bobbing an dtongue-flicking behavior (D . G. Barker , pers . comm.).

The Montaue Formation Seri es, Steppe Thickct an d Scmb D es­ert as defined by Wagner (1964) ar e habitats in which C. l. klauberitypically resides.

Jacob and Alt enbach (1977) described sexual di chromatism inbody coloration in C. l. klauberi from New M éxico, Sonora an dChihuahua. Van Devender and Lowe (1977) reported similar sexualdichromatism in thi s race from Chihuahua. We have see n tw elvesnakes from Arroyo Mest eño (7 ma les, 5 females) whi ch exhibi rsexual dichromatism. A female gave bi rth to five young on 18August 1977. Two mal e young w er e only sligh tly mottled wi thblack speckling and black bands, whe reas the two femal e you ngwer e gr ey, mottled w íth black speckling aneI had dark grey bands.The fifth neonate wa s defecti ve, exh ib iting a fusio n of th c ven tralsurface in the lower cervical ar ca and th e anterior tru nk region(UTA R-6946).

Crotalus lepidus maculosus. C. l. maculosus (Fi g. 14) is a re­cently described ra ce of rock ra tt lcsnake (Tanner, el al., 1972)whose geographic distribution rerna ins vir tually unknown becaus cmuch of its habitat is inacccssibl c. It is a resident of th e Pac ífícversant of th e Sierra Madre Occidental , and apparently intergradeswith C. l. klauberi on the high Mcxicau Plateau in th e vicínity ofEl Salto, Durango,

Whore th ey are most abunclant Crotalus l. maculosus aneI an ­other subspecies C . l. morulu s appurcntl y prefer sim ilar habi ta tconditions. Both races seem to prefer h urnid , pin e-oak for ests w ithwell-defined rainy seasons (Fig . 15). We ha ve un successfu lly tri edto obtain both subspecies in th e late spring. However , after th esummer rains bcgin, the tw o subspecies apparently sur face andare quite common. This is unlikc many populat íons of C. l. lepidusand C . l. klauberi, whose com bin cd d istribution divides the rangesof C. l. maculosu s and C. l. morulus, and have adapted in som ear eas to des ert or chaparral conditions, These pop ulat íons ar e activeabove grouncl throughout th e year if th e weathe r is sufficientlywarm (24°C). Almost all specime ns of C. l. lIlaCUlOSlIS ob taincd byus were secured under cloudy or partly cloudy conclitions, and werepartícularly cornrnon just befare and af te r showers durin g th e rainyseason. On 10 Jul y 1973, a fem ale was observed on a southcas ternfacing rock outcrop 4.8 km \V El Alazán, Sinaloa, with eleven young

26 SPE C LAL PUBLICATION-~IUSEU~I OF NATURAL HISTORY

F IG. 14. Cro talus lcp idu s maculo sus. Spec imen Irom Los Bancos , Durango,Mevico . ( Photograph by [ ohn H. Tashjian .)

eoiled or draped about her. This rac e exhib its behav íor typícal ofall subspecies of C. Iepulus in that it is alert and quick to seekshe ltcr wh cn di scov ered, Crotalus l. ma culosu s posscsses an un­usuall y sma ll rattle, and it is barcly audib le cven in Iarger spccime ns.The acce ptcd teehnique historicully employed to diseover C. lepidusin its native habitat (by hearing th em rattle) is virtually uselesswhc n trying to collcct thi s sub spccies .

Xlost of the snakes obse rve d by us, which total fort y sigh tings(KU 15553:2-534, UTA R-5847), were nonnally loeated by exploringsou the rn facing slopes wh ere an abundance of grass and rack s oceurin breaks in th e pin e-oak for esto This subspccies wa s not found inrac k slides as were lllan y C. l. lcpitlus and C. l. klouhcri populations.Howcver, C. l. m aculosu s is usuallv found near sorne kind of rackcover. Lizards of the ge nus Sceloporus appear to be the main fooditem of thi s ratt lesnake .

Other ra tt lesnakes found in assoeiation with C. l. maculosus areC. p . pricci , C. 1Il010SS11 S nigrcscens , aud possibly C. ic íllardi lIle­ridionalis in the eas tern part of the rangc. Sorne local residentsgave positivo iden tifica tion of C. IV. meridíonalis from photographswhich we provided.

Crotalus l. uuiculosus inhabits thc Pine-Oak Forest and Pine­Oak \Vood land as defined by Leopold (1950).

Croralus lepidus morulus , Crota lus l. morulus (F igs. 16. 17) isthe least known of the subspeeies of C. lepulus. This raee was de-

THE NAT URAL HISTORY OF MEXICAN RATTLESNAKE S 27

F IG . 15. Hahit at of Crotalus Iepidus maculosus, G. pricei pricei and G.molossus nigrcscens. Los Ban cos, Du rango, Mexico. Steep hillside s coveredwith pine-oa k Iore st , Th ese sna kcs werc most Ircqucntly cncoun tered inop en arcas of ra ck outcrop pings. (Photograph by R. Ter ry Basey . )

sc ribcd by Klauber (1952: .52) from specime ns obta íncd fro m P. S.Mart ín, who coIlec tc el in th e Cómez Farías arca of Tarnaulipas.Mo st of th e kno w n specimcns h avo bcen collectcd in th e CómezFarías arca , and an add ítional spec imen is known fr om Chiche (Mar­tin 19.58 : 78), which is northwest of C uidad Victoria, T amaulipas .

Rcc ently, more snakes of th is race have becn secu red iu th eSiena ele San Francisco (11. S. lI arri s, per s. comm.), and w« havelocatcd an apparen tly isol a tcd po pulation (19 spcc ímc ns) in th eSierra Mad re Oriental sorne 24-32 air kilor u ctc rs nort hwest ofGaleana near the Nu evo L e ón-Coahui la borcl er (KU 159360). Nodoubt, mo re C . l . inorulus \ViII be collecte el whi ch \ViII filI th e pres­en t gaps between th e Icw p resentl y known localiti es.

Xlos t of th e ra tt lesnakes collcc tc d bv P. S. Martin werc locat eelon th e h umiel, eastcrn slopes of th e Sierr a de Guatemala at altitudesran gin g from 1190-1890 m. These sna kes we re usuall y found alongth o ab undan t rocky mounta íu trails in th e Góm cz Farías area. Pines ,oaks, ami firs cons tí tu te th e major vcgc ta tional formation of thi sarca, alt ho ugh th crc is an ab undance of agave on th e stccp rockysides of th e Sierra . Martiu (1958) stated th at C . l. m orulus wasp resent in th e upper p art of the Cloud Forcst, but it s presen ce wasnot confirme d in th e Lo wer C IOlH] Forest. This arca is extrcmelyru gged, ami more exte nsi vo coIlec ting is needed to delineate th eexte n t of th e ra ngo of C . l. morulus.

28 SPEC IAL PUBLICATION-MUSEUM OF NATURAL BISTORY

" ... ~ .

FIC . 16. C rota lu s lep idus morulus. Specimen from near San Antonio delas Alazana s, Coahu ila, M éxico. ( Photograph by John H. Tashjian .)

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FIC. 17, Cro talus lepid us iuorulu s. [uvenile specimen bom to fema lc col­lecled nea r San Antonio de las Alazanas, Coahuila , Mexíco . (Photograph byJohn H. Tashj ían . )

TH E NATURAL HI STOHY 0 1" ~IEXICAN RATTLESNAKES 29

In lat e August 1973, Danial Lopez and onc of li S (BLA) collcct cd16 spccíme ns of C. l. morulus 24-32 km northwest of Calcana; thcspe cimcns ran ged from maturc adults to newboru youn g. All wereidentified as C. l. morulus in having at least 28 prímary dorsalblotch es w ith th e exce ption of au adult fem ale which had 19blotches and no mottling . This female gave bi rth, severa ] da ys af tercap tu re , to Iour young wh ich had th e normal complem ent of pri­mary bl otch es, suggesting th at the Iema le par cnt exhihited an ab er­rant pattern, not uncomm on in th e C. le pidu s complex. D ur ingsumme r 1974 an add itional indivi dual (UT A R-6123) was tak enfrom th e sa me localíty in a p ine-scrub oak situa tion on a steeprock y hill sid e.

Unlike th e specíme ns collected by Mart ín which wer e associatedwith humid pin e-oak for ests at th e elevations pr ev iously mentioned ,all of th e specimc ns obtained by liS were locat ed at clcva tions be­tw een 2380-2592 m am on gst limesto ne bedrock which had a south­ern cxposure , A fcw sca tte rcd p inos and oaks were pr esent, butmost of th e vcgctation cons istcd of va rious spccics of ag avcs andlow growing sh rubs , whic h provid cd exce lleut cov er for th e snakcs ,These snakes appcared to be extrc mc ly common during th c onlyFour hours wc spent collccting (d ue to inc!em ent wc uther) an dwould oft en make th eir presen ce known by rattling lon g bcforc wewere within th eir vicw, Thcy would imm ediatcly seek shelteramo ng th e rocks an d agaves, and sevc ra l escapcd us in this hab ila t.Captured snakcs defended tliemselves vigorously ami often b il them­selves 01' the tongs that wcr e uscd to secure th ern .

This subspecics has bccn rcported Irom th e Hu mid Pin e-OakForest to Pine-Oak Forest (Martin 1958).

Crotalus mitch clli (Cope)

The spcckled rat tlesnak c, C. niit chcllí , is un in luihi taut of theAme rican Southwest, Baja Ca lifamia, islands in the C ulf of Ca li­foruia , ami onc Isla nd, Santa ~ (argarita , off the Pacific coast of BajaCalifornia del Sur (Klaube r 1972). I t is a highl y variab le ra ttlcs uake,both in sizc and color , and to a lesser dcgree in pat tern. Co lor an dpatte rn sec m to be co rrelat cd with the general color of th e rock yterrain whic h any givcn populntion inha b its.

Crotalu s mit chelli m ítchc lli. The San Lu can suhs pcc ics, C. I/ /.

nüt chclli , rangos fro m the southcrn hordcr of Baja Californ ia delNorte, south th rou gh out the pen ínsula. Island popul ations a re 10­catcd on Ccrra lvo, Es pirilo Santo , San José, Carmen , ami SantaMargarita lslands (Klaube r 1m2). Thc rango do cs not includcSanta Cruz Island (Soulé ami Sloan 1966). This rattlesnake is COI11 ­

mon through out its rang e, but is most easily ob scrv ed in thc Ca pereg ion. Klauh cr (1936) rccordcd specimc ns from Ca pe San Lucas,San José del Cabo , Miraílores, Todos Santos, La Paz, Muleg é,

30 SPEC IAL PUBLICATIOl\'-~fUSEUM OF l\'ATU RAL HISTORY

San ta Rosalia , and San Ignacio. Specim en s obtained by us ar efrom 8 km N San Jo sé del Cabo and 16.1 km N Bu~na Vista(KU 173097).

Crotalus m. mitche lli is a dweller of th e rocky portien of BajaCaliforn ia. Rarely \ViII it be found an y distance fro m rock y re­tr eats, and it seems to prefer rocky canyons and rock outcrops(B. Tomberlin, pers. comm .). This rattl esnake has, however , b eenfound on d esert flat s where desert sh ru bs and burrows provideshelte r. Crota lus e . c ruj o an d C. ruber lucasen sis are often foundsyrnpatrícally wi th C. 111 . mitchelli, although the first two ar e notas prevalent in rock y situations . Klauber (1972: 536) found thatC. 111. mitchclli was a rock dwcll er, but also indica ted it wa s foundin b rushy a rca s. Most of th ese ratt lesna kes a re nocturnal , sincetemperatures in southern Baja limit diu rn al ac tivity. Acti vityreaches peak pcriods du ring th e lat e summer rainy seas on. Theserattlesnakes ar e most oft en ob served at night as th ey are crossingroa ds.

A ca p tive pair of C. m . mitclielli was observed in copulo on13 Octob er 1975 at 0800 hours. The rig h t hernipcnis of th e majewas inserted , an d a promincnt bulge was evident which extende dten scale rows an terior to th e vcnt of th e fem ale. The snakesseparated at 1500 hours. On 29 Jun e 1976 th e female gave birth toone neo na te and on e inf ertile eg g mass. The newbom snakemeasured 275 mm in to ta l len gth, S-V 263 mm , weight 17.5 g(UTA 1\-6939).

The Seasonal F ormation Ser ies an d Cactus Scrub and Savannahas defined by W agn er (1964) are typ ícal vegetative regim es in­ha b itcd by C. m . tnitclielli . These arca s support mesquite, creosotebushes (Larrea), cacti and other arí d vege ta tion (Goldman 1951).

Crotalu s mitehclli pyrrhus . A sou thwe stern subspecies , C. 111.

pijrrlius, is a rock-dwelling rattlesnake that ranges in M éxico fromthe Californ ia border to the southern portion s of Baja Californiadel Norte. Thi s ra tt lesnake is common on th e desert portions ofth e Sierra Juá re z an d Sier ra de San Pedro M ártir. It is also foundon the wcstcrn slopes in chaparral sítua t ions , but not commonly .T\Vo ra ttles na kes obtained b y liS fro m south of Pu ertec ítos wercfoun d in th e v íc ínity of abando ne d sul phur mines in extremelyrock y mouu tains , They wer e found just afte r sundow n in earlysp ring, a period of th e year that seems to be a peak activ íty tim efor C. m . pijrrhu s , ' Ve have obser ved ma ny individuals of thissubspeci es no rth of the U.S. border in sou thern San Di ego County,California, during early spri ng . Fewer specimens were found dur­ing summer an d fa ll. 1'0 take advantage of favorab le ambient ,tem­peratures, this rattlesnake shifts from a diurnal mode of activityin th e spring and fa ll to noc turnal act ívity in th e summer (Moore1976).

TIIE NATURAL I1ISTO RY OF MEX1CAN RATTLESNAKES 31

Crotalus m. Purrllll s inha bí ts th e Ca lifornia Chaparral, SeasonalForrnation Seri es, Cactu s Scrub , and Montane Th icket as dcfin ed byW agner (1964).

Crotalu s mitch clli mucrtcnsis. A dwarf subspecies, e. m. mller­tensis, is an ins ular fonn of e. mitchcl li from El Mu erto Island ofth c San Luis group in the Gulf of California . El Muerto is th csecond largest isla nd in th c group, is found ca . 6.4 km southcastof Hu érfanito Island (thc northcrnmost island in thc San Luisgro up), and ís an extrerncly arid, rock y island supporting sparsevcgcta tion. D ur ing th e summer , tcrnpcra tures on the island reachhigh extr emes and limit reptilian act ívity.

Sixtccn specimens ob ta incd b y us (KU 155535, 174830) weretak cn from th c westcrn and southwestcrn portions of th e island on30 May 1969 bctw ccn 1000-2000 hours , most w er e releascd aftcrcap tu re. The ma jor ity of th ese spc cimc ns were found shortly aftersunset, sincc dayti me tern perature rea ch ed approximat ely 38°C.Severa l specimens werc found within 3 m of th c wat er , foragingin beach deb ris. Othcr spccimens were Iocated on rocks, and somcwere fou nd und er sparse bush cs. A single sp ecim cn was recordcdat 183 m elevation, Two lizards, Uta siansh uriana and Strepiosaurusmearn si , as wc l! as a spccíes of Perouujscus, occur on th c El Mu ertoIsland in lar gc numbers, and probably mak e up a sizab le po rtien ofth e diet of e. m. IIlllertell sis.

Th cse dwarf ra tt lcsnakcs would rattle lon g before w e werewithin 6 m of th ern , in di cating a hi gh degrcc of alert ness. Severa]índividuals escape d under massive rockpiles before we wer e ableto observe th cm. T hosc captured resist ed vigor ously, and allthrashed vío len tly. A1though all wcr e obs erved bcfor e sundow n,it is reasonable to assum e that e. 111. m ue rtensis is mostly no cturnalbecause of excess ívely high daytime temperatures.

T wo of th e sna kes ca p tured by us brcd in captivity on 2.3 March1977. At the time of collection , th c mal e mcasured 355 mm, andthe fcmale 280 mm, in tot al lcngth. At th c time of b reeding, th cmalc measurcd 680 mm, and thc femalc 610 mm , in total lcn gth.Two liv c an d two dcad young (UT A R-7218-1 9), and thrce infertil ema sses, we rc born on 13 Scptcmbcr 1977. Total len gth of th c fouryoung, measurcd an d weighcd eigh t da ys after birth, was 143-179mm (mean 167) an d w cight was 3.3-7.0 g (me an 4.9).

Crotalus m. muertensis inhabits th c Seasonal Formation Seriesand Cactus Scrub as dcfined by Wagner (1964) .

Crotalu s m olossus Ba írd and Girard

The blackt ail rattl esnakes, e. molossus, of the Ameri can south­west and the cen tral pl at eau of Mexico, are well known th roughoutthci r rangc dcspi tc the fact that they werc at tim es confused wi the. basi iiscus (Gloyd 1940: 161; Klaubcr 1952: 87). Largc collections

32 SPECLAL PUBLICATlO!\-MUSEUM OF NATU RAL HIST ORY

of th e subspecíes C. m. molossus and C. m. nigrescens have beenma de in past years, and onl y C. m. cs tc bane nsis, from San Es tebanIsland in th e Gu lf of California, remains b íologica lly unknown .AH three subspecíes of C. nio lossus attain mod éra te size , and speci­mens of C. //l. niolossus and C. //l. nigrescens are among th e mo sthandsom e rattlesnakes we have had th e opport uni ty to observe.Thís rattlcsnake appe ars to b e adaptively succcssful; th c range andvaríety of habitats within its area of distribution are unsurpassedby most othe r Mexican rattlesnake spccíes.

Crotalus molossus mo lossus, Crota lus m. niolossus lives in di­verse ha b íta ts from th e Edwards Pla teau in west-central Texasthro ug h Arizona to the Grand Canyon . In Mexíco, C. //l . m olossushas been reported from th c states of Sonora , Chih ua hua andCoahuila; it intergrades with C. //l . Iligre scells in th e southern por­tio n of its range. See Klauber (1952: 91) for a discussio n of inte r­grada tíon in th is species. Specimen s obtaincd by us have beenrecorded fro m: SO.:\'ORA: 4.8 km S Sonoyta ; CHIHUAHUA: theSierra del Nido complex, 16 km S Chihuahua. \Ve have observedapproxírnate ly 30 individu als,

AIthough sornewhat un spccial ízcd ecologically (Dammann 1961),C, //l. m olossu s is gencraIly con sid crcd a montane species, p re­ferring rocky retreats within dominant pinc-oak fo res ts. Typ ícalhab itat nichos for thi s rattlcsnake from mountain ranges such asth e Ch íricahuas and Huachucas in southe rn Arízona, an d th e Sierrade Ajos and Sierra del Nido of northern Xlcxico, reflects th is prefe r­ence. This snake is oftcn observcd a t h igh elevations (up to 2592 m)in th e Chiricahua Mountains of Arizoua. However, it app cars tobe more common below 2135 m on southe rn or southeas tern facingslopes of the Chiricahuas wh ere oak , madroño, agave, and va riousgrasses a re th c dominant vcgetatíon. Pough (1966) observed manyin th e talus rocks lides where C. lepidus klauberi is qu ite commonand our observa tíons corroborate those made by him. Rock y str eambeds are aIso inha bited by C. 111. inolossus, especiaIly dur ing th esummcr rain y seas on. C. //l . molo ssus is not rcs tricted to forcs tedmountains, however, as Klauber (1972: 537) cited spccime ns fromthe valleys an d plain s of Cochise County in Ar ízona which averageca. 1220-1525 m clevation, \Vc have ob servcd thi s subspecies indesert situations north of Scottsclale, Organ Pipe National Monu ­ment, ancl near Ga tcs Pass, south of Tucsou , Arizona. Ta ylor (1936:497-498) found C. 1/1. //l OIO SSIl S to be common in rocky habitatsnor thwest of Cuaymas at La Posa, whi ch is near sea leve !. Perhapsthc most unexpected place wh ere thi s snake has bcen found is th csand dunes south of Cuida d Ju árcz in Ch ihuahua, where a spccí­men was taken by T. \ Valk cr (pe rs. comm.).

Most C. //l . molossus are gentle in di sposi tion an d generally seekescape when approache d. They rarcly rattle, although those fou nd

THE NATU RAL IlISTO RY OF ~IEXICAN RATTLES:\'AKE S 33

in rockslid es will at times reveal their presence by ra ttling, a char­ac teristic they sha re with C. lepid us and C. pricei . Allen (1933)found C. m. molossus in trees ca . 2 III aboye the ground.

C. m. molossus ínhabí ts the Seasonal Formation Seri es, Montan eFormation Seri es and Scru b Desert vege tational classifications asdefined by Wagner (1964). See Gloyd (1937) and Low e (1964) fora descripti on of th e habitat of thi s race in Arizona.

Crotalus molossus nigresccn s. The Mexican blackt ail rattle­snake, C. m. ll igrescells (Fig. 18), is generally a resident of temperatepin e-oak fores ts of the central plateau of Mexico, anel Gloyd (1940:164) listed localit ies for every state within th e plat ean. \ Ve haveobserved tw enty snak es from the following localities: D URAi'\GO:17 km N Las Nieves (UTA R-5630), 16 km W Dur ango, Los Bancos,8.3 km E Coyotes (UTA R-.5700), La Ciudad; JALISCO : W Za­coa1co; ~nCHOACÁN : 4.8 km S Ca mpan, Contep ec, 7 km WMorel ía, Morelia (UTA R-5112-4), Tacícuaro; ~IORELOS : th elava bed s off th e toll road hetween Mexico Cit y and Cuernavaca:VERACR UZ: th e lava beds near Perot e.

Crotalus 1/l . nigrescens does not occupy as many varícd hab itatsas C. 111. 111olosSIlS, but is not restri cted to a spec ific environment ,Indi vidu als were observ ed by us ncar Las Nieves, Durango, in rockoutcrops at 1220 m withi n an oak-grass savannah. They were com­mon th ere, an d th e local resid ents wer e wc ll awa re of their pr csence.The other previously listed locales in Du rango wer e typ ically pinc­oak situa tions whcre broken rock and var ious gr asses pro vided

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-FIG. 18. Crotalus 1/I0/OSSI/S nigrcsccns. Specimen from near Morelia,

Michoac án, M éxico. juvenile . ( Photograph by ] ohn H . Tashjian. )

34 SI'ECIAL I'U BLICATI01\-~IUSEm. 1 OF :-':ATU RAL HISTORY

excellent cove r and a var íed food supply (Fig. 15). Most of thera ttl esnakes observed by us from thesc areas in D urango wcr e foundbasking in the lat e morni ng duri ng the july-August ra íny seaso n.Those from Carapan, Michoac án, Pcrote, Veracruz , an d nor th ofCu ernavaca, Morelos, we re a1l locat cd in lava bed areas. Davisand Smith (1953: 141) tho ught that the occurrencc of C. m. nigres­cens in Morelos was doubtful bascd on geographic grounds, AtCarapa u in Michoac án thcy were extremely comrnon (10 obscrvcd) .Th e spec ime ns from Tacícuaro and Contepec, Michoac án, were inmesquite grassland, a hab itat in wh ích Klauber (1972: 538) hadpreviously specula ted that this subspecies might occur. J. R. Di xon(pers. comm.) found a specimen in swect-gum, oak Iorcs t on th ceast-facing slope of Sierra Madre, 11.2 km E NE Pinal de Amoles,Querétaro, a t 1981 m clevation.

D unkle and Smith (1937) found a fcmalc C. m. ni grescens with16 young in a canyon wes t of La Colora do, Zacat ccas. Cop ulatio nwas observ ed by us between a captive pair on two occasions (28May 1973 and 2 Ma rch 1974); no pul sations or othc r movementswe re noticed. No young were born from th ese obse rved un íons,bu t on 9 [ une 1975 five young were bo rn in captivity, and wereweighed aud measured . Raugc of variation is as foIlows: totallength 291-316 mm (mean 304); S-V 267-290 mm (mean 284); wcight25.4-27.9 g (mean 26.6).

Two C. 111 . lI ig rescell s were observed copulating on 1 February1978 at 0920 hours. T he d iarne ter of the fema lc's cloaca was 15 mmand wa s distended due to thc male's hemipen ís. A noticcable bulgein the Ieuiale's body extended 35 mm an terior to hcr cloaca. Theshoulder spines of th e hemipenis wcre visibl e and the organ wasda rk pu rp le in colora tion. Coitus lastcd 105 minutes and detu­mesccn cc of thc hemipenis occ upied 100 seconds. 1ntcnnitten thead-bobbing and tongue-Aicking seque nccs by bo th snakes oc­curred during coitus.

An open mouth defensiva postu re was observed in three indi­viduals, Thc rnouths were hcld ope n for over five minutes whenthe snakcs were provoked ,

The subspecies C. 111. nigrcsccIIs ínhab íts the Temperate Pine­Oak Forcst as defined by Leop old (1950) and Mesquít e Crassland(Klaubcr 1972).

Crotalus poltj sti ctus (Cope)

Previous accounts of Crotalus polijsti ctus indicated a preferencefor marshy situa tions and this snakc was genera lly rcferred to asthc "aqua tic rattlesna kc." This prcsumcd preferencc for aquati csitua tions was rcin forced by specimens, captured in 1919 b y PaulD. R. Ruthling, whi ch wc rc sccurcd in thc tules of Lake Chapala,Jalisco (Klauber 1956). However, th is was probab ly an unusual

THE NATU RAL IIlSTORY OF .MEXICAN RATTLESNAKES 35

situation since Huthling pointed out that thi s area was, at the timeof coll ection, a flooded swampland. In thi s ephemera l environment,it is easy to understand why so ma ny specimens (20-25) we re ob ­served by Ruthl ing , and also wh y th e spccies was though t to preferan aquatic habitat . It is unlik ely for a snake with a warning mech­anísm such as a rattle to live in aquatic situa tions where the ra tt lewould be rendered useless.

In recent years wc have captured or observed over 100 specí ­mens of C. polusti ctus in the vic ínity of the Nevado de Colima insouthern Jali sco (Fig. 21) and northern Michoac án. Smith andHigareda (1965) comme nted on specimcns fro m th is area. 1n Jalisco,this snake ha s be en found on plat eau s which occur in breaks inthe pine-oak forest at eleva tions of 2075-2317 m. Often these arcasare interlaced with gently Ilowin g streams. This rattlesnake canbe found during most months of the ycar: we have records fromDeccmber , Feb ruary, and May through September. Snakes ob­tained b y lIS ar e from th e follow ing localities: JALI SCO: nearChapala (UTA H-4000), Ran cho San Francisco (UT A R-4499, 4906-S,4916,5666-7,6043,6250,6704,6822-23,6927; Figs. 19, 20); :\IICnO­ACÁN : Ta cícuaro (KU 155540-541), 8 km \V Morelia, 18 km \V[ íquilpan, .5 km 1'\ Cato de las Esperanzas.

Most C. pohjstlclus are foun d in rocky situa tions with an abun­dance of tan gra ss called zacaton. Nono of these rattlesnakes haveas yet been discovered in pine-oak fores t, but thcy muy occur intliat hab ítat . In Míchoac án, near Ta cícuaro, C. polustictus has been

~~';.'~''(: .':':': :':>~? -: ;~: .~ .• ~ -J...

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. ,' ...~ ~

FIG. 19. Grata/lis pO/!lStict IlS. Specirnen from Rancho San Francisco,Jalisco, Mexico. (Photograph by [ohn H . Tas hjian.}

36 SPEClAL PUBLICATION - 1IUSEU M OF NATURAL HISTOR Y

.-.

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I

FIG. 20 . Crotalu s pohj sti ctus. juveni le specime n bom lo female collecte d atRancho San Francisco, Ja lisco, Mexíco. ( Pho tograph by [ohn H. T ashj ían .)

FIG. 21. Habitat of Grata /lis nalusti ctus. Rancho San Francisco, Jalisco,Mexíco . Sna kes were com monly Iound among boulders or in gophe r burrowsin gra ssy mcadows wít h surrounding pi ne forest on hill sides. (Photograph by11. Cranger.)

THE NATU RAL HI STO RY OF ~IEXICAI\ RATTL ESNAKES 37

co llected in mesquite grassland (D uelIman 1965: 655). This areahas rocky outc rops where th e spec ies is eas ily located . W e havealso co lIected thí s speci es in pla ins-grassland areas, although it do esnot appear to be abun dant in this env ironment,

Cr otalus pohjstict us is found rather comrnonly in lat e sp ringwhen summer rains have no t yet been sufficiently heav y to con­tr ibute to growth of grass cov er . During thí s period, th ey becomesornewha t noc turnal, active ind ivid uals hav íng been recorded aslate as 2200 hour s. In late spring , C. polystictlls d íspl ays a rathermild di sp osit ion and is usuully quite inoflensive. Sorn e spe cimcnshave been observcd attempting to hiele their head s ben eath a coilof their bod y, behavior sim ilar to t hat exhibite d by L ichanuratri oirgata roseoj usca. Dur ing the summe r, th ís specics becom esmuc h mo re aggress íve and will gen er aIly no t retreat wli en ap­proach ed. \Ve observed an individual which, upon d iscovery,ope ne d its mo uth in a th reat ening pose similar to th e hch avior ex­hibited by Agkis t rodo n piscicoru s. Lam propeltis tr iau gulum ar­cijera, a harmless co lub ricl snake, is corn mon in th e vic inity of th eNevado de Co lim a, an d ma y be an important pred at or upon th eserattl esnakes.

The kno wn ran ge of C. polysti c tlls is decreasin g du e to habitatdestructi on. The plat eados iuhabitcd b y th ese rattl esnakes ar e be­ing alte red for agricultu ra ! use bccausc they are mo re easily clea redth an ad jaeent pi nc-oak for est s.

The preferred habi ta t of C. politstictus is Tempernte Pine-O akFor est as defined by Leopold (1950), and Mesq uite Crassla nd(Due llman 1965).

Cuesta T erron (1930-31) rep orted on a b rood of 14 newbornyoung wh ose average tot al len gth was 12 cm , a figure con sidcrahlysma lIer than th e mean to tal Icn gth of brood s measured by uso It ispossibl e th at Cues ta Terron ma )' hav e misidentificd his snakes (seeFi g. 6, p. 54), a ltho ug h we have not seen his specimcns.

D at a a re available to us for six brood s born to females of th isspccies, as folIows: Female A, ",eighing 111 g anel measuring 608 mtotal length (575 mm S-V), gave bí rth to ten yo ung on 20 [une1974: total length 200-223 mm , mean 211; S-V 184-208 mm, mean195; w eight 6.3-10.9 g, mean 7.2. F cmale 13, weighing 166 g aneImeasuring 660 mm tot al length (620 111m S-V), gave birth to tw elv eyoung on 13 June 1974: total length 211-287 mm , mean 222 ; S-V198-271 mm, mean 208; w eight 8.5-11.5 g, mean 9.9. Femal e Cgave b irth to sev en young on 26 Ju nc 1975: to tal length 198-232mm , mean 216; S-V 185-211 mm , mean 200; w eight 9.9-10.5 g ,mean 10.1. Fcmale D gave birth to seven neonates on 30 june1975: tot al length 182-205 mm , mean 197; S-V 167-185 mm, mean179; w eig ht 9.9-11.1 g, mean 10.6. F ernale E gave b irth to Iivest illborn young on 30 june 1975: total len gth 155-203 mm, mean

38 SPECIAL PUBLICATIO;'\J -~I USEU~I OF "ATURAL HISTORY

177; \Veigh t 2.4-S.,') g, mean 4.0. F emale F gave birth to sevenyou ng on 25 June 1975 : total len gth 227-239 mm , mean 232 ; S-V201-219 mm, mean 212; weight 9.5-10.9 g, mean 10.2. Th e rangeof variation of th e six brood s is as Follows: total length 155-287mm , mean 2.14; S-V 167-271 mm, mean 201; weight 2.4-11.5 g,mean 8.9. '1'\\'0 of th c snakes b orn to Fcmale A were maintained incaptivity an d exhibi tcd eourt ing bc havior on 31 j anuary 1978 .

C rotalus pri cei Va n Dcnburgh

Crotalus pricei prieci. Crotalus p . pricei (F ig . 22) is the morecommonly known subspecies of th is sna kc , Iargc collections havingbecn madc in Santa Rita, H uachuca, Chirica hua , and GrahamMountains uf sou theastcrn Arizona . Fewcr inclividuals of th is racehave becn rccordcd from Xlexico, yet th ey a re ra ther abundant ini\lexico in pine-oak forcsts a t elcvations ra ng ing fro m 2135 to atleast 2745 m. \ Ve have observcd th ese rat tlesnakes from th c fol­lowing localities in ~I exico : SO?\OHA: Sie rra de Ajos (UT A1\-6931 -34); C HI HUA HUA: th e Sierra del Nido complex: DU­RA:\GO : Las Adjun tas , near Coyotes, 14 km El\'E El Salto (UT A1\-2(21), Llano Crande (I\:U 158561), Los Bancos (UT A 1\-6251).Klauber (1972: 45) suggcstc d that C. ¡J. pricei mal' al so OCCIII" ineas tcrn Sinaloa and no rt hern l\'ayarit, bu t to 0 11I" knowlcdge, nospccimens have becn scc u rcd in ci the r of th ese states.

Crotalus p . pricci is a res idc nt of hi gh rocky pine-covercd slopes(F ig, 23). In thc Unitcd Stat es, it secms to prefer talus rock slides

1'1 (;. 22. Cro talus pricci price i. Spec imen frum near Los Bancos, Durango,Mexíco. (Photograp h by [o hn H . Tashjian .)

THE l\'ATU RAL HISTORY OF },IEXICA0: RA.TTLESNAKES 39

in th e previously ment íoned mountain ranges. This rattlesnake willofte n clivul ge its presen ce b y ra tt ling when ap p roache d. H owevcr,lik e many of the montan e ratt les nakes, C . p . pr icei is eurious anelusually ret reat s onl y a short clistnnce. Altho ugh genemlly asso­cia te d with roc ks, this ra tt lesnake mal' b e founcl also in grassymountai n va llcys whe re prcy, such as lizar cls anel small roclen ts, isabundant. One aclult sn ake (UT A H-20:21) containecl a juven ilelizarcl (Scc loporus po inse tti} . \Ve ha ve frequentl y observecl th issubs pecies on w arm, humid days w hen clifl usecl sunligh t is preva­lent. 1ndividuals were co llecte cl ne ar rock y re tr eats from March toNovernber , even when a light sno w cover was presento No cloub tth ese retreat s a re th e warmest micro-habi ta ts avai lable to thi s rattle­snake in moun tains . On 17 Xlarch 196.5, two C. p. price í were founclon a sou th-Facing talus slope a t Burfoot, some times kn own as BuenaVis ta Peak, Chi rica hua Mo untains, Arizona a t 1:2:20 hours . Snowsurro unclecl th e talus slope, an d the ambien t tem peratu re was 11oC.

In Mexico, C. p . pricei is p robably th e most comm on rattl esnak ea t higher e leva tions within its range , where it is founcl sym patricallywith C . icillardi, C . lepidus, un d C . 1Il 0 10 SS11 S. W e ha ve collec teclC . p. pricci fro m Ma y through September , som etimes u ncle r themost adverso weather condi tions, 1n ] une 1973 w e secu red fou rind ivid ua ls on a sou th- faci ng slope nea r Los Ba ncos, Durango (F ig .

FIG . 23 . Habitat of Crotalus pricci pricci and G. icillardí m cridionalis.Sp arsc pine-oak forest near Lla no Grande, Durango, Mexico. C rotalus p .pricci was ge ne rally d iscove red in rocky areas wh íle G. ui, incridtonalis wascol1ectcd in thi ck grass or un derbrush , mainly man zanita and scrub oak, 0 11

hill sides. ( Photograph by Lyndon A. Mit chell . }

40 SPEC IAL PUBLICAT IO~-~IU SEm.1 OF l\'ATURAL HISTORY

15), two hou rs afte r a d rivin g hail ston n. T he hail melted qu ícklyand a ll Iour snakes were act ive, appare n tly foraging for food .These Iour snakes exh íb itcd an unu sual a rray of body patt erns .One indivi dual lia d the ty pical colora tion of a sla te -gray b ack­ground with brown do rsal spots. Th e second cxa mple exh ibite d ab lue-gray backgro un d wi th rus ty colored spots. The third spe cimc nwas overall salmon-pin k wi th tan spo tting , and th e Iourth snakewas a completely patternl css light ta n. These four spe cime ns werecapturcd w ithin a 45 m ra d ius,

A Iemale specimc n of C. p . pricei obtained a t Lo s Bancos,Durango, gave b irth to three young 011 24-28 j uly 1973. AnothcrIemale, tak en near On ion Sadd le, Chiricahua Mouutains, Ari zona,gave b irth to Iour youug on 20 Xlay 1967. Thrce young C. p . priceiwere found on 11 july 1973 near Lo s Bancos, D urango, in a rockcrc vice: th ey had not she d. A ca ptive mating produccd Iour youngon 9 july 1971 (J. A. Ca mpbcll. pers . comm.). Three of th e fouryoung were born ali ve al\(l wcigh ed 2.7, 3.9, 2.4 g ; mean 3.0. Fourfemale specime ns from Llano Grande, Durango, gave birth in th elab or atory on 10, 14, 27, and 29 [ uly 1977, respcctí vcly. D ata onth esc [ou r broods is as Iollows: F cmale A produced eigh t young(2 sti llborn, less th an 50 mm total le ng th), total Iengt h 157-167 mm,mean 164; weigh t 4.0-4.2 g, mean 4.1; F ernale B gave birth to nin eviab le young (four di ed w ith in tw o days, UTA R-6935-8), tot allen gth 152-173 mm, mean 162; weight 3.5-4.0 g, mean 3.6; FcmaleC gavc bi rth to six via ble young , total leng th 159-169 mm , mean162; weig h t 5.1-5.6; F emale D produced six young, to ta l Iength160-1805 mm, mean 168; we igh t 3.6-3.9 g, mea n 3.7. The range ofva ria t ion an d mean for all litters was as Iollow s: to ta l length 152­185 mm , mean 164; weight 3.5-5.6 g, mean 4.1. Al! but one of th eFernales were collec ted wh ile b askin g in th e early moming onrocks (L. A. l\litchell and D . G. Barker, pers , corn m.). Kauffeld(1943a. 1943b) rep orted th at an example of C. p . pricei collected atBarfoot, Buen a Vis ta Peak , Chiricahua Moun tains, Cochise Cou nty,Arizona, gave b írth to six young on 19 August. He citcd anotherrecord of a brood of th is race born on 3 August 1941. Kcasey (1969)recorded a b ir th of eigh t young on 23 Septem ber 1953. Six youngwer e born on 19 }ul1' 1971 to a fcmale sec ured at Los Leones ,Chihuahua (Van D evender and Lowe 1977).

C . p. pricei inhab its th e T cmpcrute P íne-Oak association as de­fined by Leopold (1950). Sce Cloyd (1937 ) and Lowe (1964 ) for adescription of th c habitar in Arizona.

Crotalus pricei m íquihnnnus . Although mu ch litcrature is ava íl­nb le ab out C. p . pricei , Iitt le is known about C. p . miquihuan us(Figs. 24, 205), no do ubt du e to th e inabilíty of col!ec tors to ge tin to the Iimited areas inh abi ted by it. Specim ens of this rattlesnakeha\'e been kno wn sin ce 1898 when Ne lson and Goldman succeeded

TlIE NATURAL HISTORY OI' :-'IEXICAi\' RATTLESNAKES 41

in capturing an adult male nea r Miquihuan a, Taumaul ipas. Ho\V­eve r, it was IIOt placed as a subs pccies of C. pri cei until the holo­typ e, a su badu lt male, was sec ured near Calea na , Nu evo León, in1938 , and described b y C loy d (1940: 10:2). Since that t ime, occa­síona l sp ecim ens hav e b een fouud bnt were unfortunatel y lost be­for e being pl aced in sys tematic co llcc tions.

Recent information, still qu ite limited , presen ts a sornewhatclearer pí ctu rc of th e apparcnt range of C. p . miquihuunus. !JI1961 an adult sna ke of th is race was co Ilec te d in the Sierra de LosAmargos, Coahuí la, exte ndi ng th e known ra nge som e thirty milesnorth from th e type local ity in ?\lIevo León (Axtel] and Sahath1963). This \ViII probably b ecomc th e range limit of thi s ra tt le­snake to th e north, s ínce th ere is a di st inc:t topograph ical aud Iaunalbreak at thi s sit e whercin a much mo re arid and desert -typ e hab ítatreplaces th e pine-oak fo rest of the Sierra \ fadre Oriental . J. H..Dixon (pers. comm.) secured th ree specimcns of th is race [rom14.8-17.2 km E San Anton io de las Alazanas betweeu 1981-2 80 -1 melc vatiou during May and August 197:2 . AIl wcre takcn Irom apiñou-pin c, aga ve slopc. South from Cerro Potos í, th e spcci mc nobtaincd by Nclson aud Go ldman in 1898 is th e onl y knowu recordfor thi s subspccies. This is not to sllggest , howcvcr, th a t th e ar casurroundiug ~fiquihllana, T am aul ipas, is th e southcnunost limit ofth e rango of C. p. nüquihuan us, Dile to topographical , Iaun al, audto some degree, geological simi larity, it is possible th at th is su b-

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-: .,.,

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FIG. 2-1 . Crotalus pricci tniq uiltuanus, Spe cime n fro m near San Antoniode las Alaza nas, Coah uila, Mexi co. ( Photogr aph by [ ohn H . T ash jian . )

42 SPEC IAL PUBLIC:\TION-~IUSEU~ I OF NATURAL HISTORY

Frc , 25. Crotalus pricei miquihuanus , [ uven íle specimen born lo ferna lecollec ted from Cerro Potosí, Xuevo León , Xlexico. ( Photograph by J01ln II .T ashj ían . )

species will eventua lly be found as far south as the San Lu isPot osí/ sou thweste rn Tamaulipas border , among th e high for este dmountain slopes .

Duri ng our travels thronghont Xlexico from 1967 to 1974, wesccu red four adult C. p. miquihuanus. Two were di scov ercd above3050 m near the typ e local íty. in mid-july 1974, in a lim estonebedrock, agave , scru b oak h ábitat at 1100 hours. They wer e bo thsunn ing on th e limeston e roek and sceme d placid ancl ind ifferentto bein g captured, u nl ike C. p . pricei which reacts defeu sively.The summ it of Cerro Potosí has been heavily dcforested , an d aluxuriant grow th of Iow -growing vcgetation, such as agave ancIscrub oak, ha s rcplaced th c ori ginal pinc forest. Ther e ar e stillman y pines in th e ar ea, hut Ce rro Potosí is no longer str íctly apin e for est. With thi s chango in vegc ta tion, the populatiou ofC. p . miquihuon us appears to have increased , possibl y the lo\v­growing shrub bery offer s more pro tection to bo th the ratt lcsnakcand its ma in food prey, lizards of th e genus Sceloporus.

A female C. p. miquihuanus, collected on th e cas t slope ofCerro Potosí, Nuevo León , at 3203 m, gave birth to five young(KU 1.5,5,542. 1.57869-871) on 19 Au gust 1974. The range of varia­tio n is as Iollows: total len gth 130-143 mm , mean 135; S-V 117-130mm , mean 121; we ight 2.6 g, mean 2.6. Another female (UT AR-6235) captured on 16 Jul y 1976 in a pin e-oak Iorest at 2652 ID,

TH E NATURA L IIISTORY OF ~lEXICAN RATTLES:\AKES 43

located 17.2 km E San An ton io de las Alazanas, gave birth to fouryoung th e Ioll ow íng day (UT A R-6175-77, 6236).

The habitat type p ref erred by G. ]J. mi q uihuan us is the T emper­a te Pin c-Oak assocíatío n (Klau ber 1956).

Cr otalus pusillus Klauber

Crotal us pusillus is a sm all rattlesnake Iound in intcrmitt entmontane hab it at s in sou thern Jal isco and w estcentral Míchoac án(F igs. 26, 27). Klauber (1972: 163) consídercd thi s tax a to b e on eof th e most primiti ve Xlcxican mountain rattl esnakes. C rota luspu sillus inhabits the p ine-oak forest s a t e lcva tions from 1.52.5 m toa t least 2380 m (Sie rr a de Coalcom án), and resides within theUpper Souoran-T ransi tion Zone as defiued b y C oldm an (1951). I toccurs sympatrically with G. t. tr iseriatus throughout its range withth e exce p tion of th e Sierra de Co al com án where possíbl y only G.durissu s culm inalus and G. !J . basiliscus live in close proxim íty .

Cr otalus pusillus is locall y comm on, amI 17 spccim ens wcrc ob ­served b y u s (UT A H-4530-1, 5846 , (119). W e found thcm to b eq uite abundan t in th e Sier ra de Coalcorn án. in clea red arcas ofhumid pine-oak forest (F ig. 28). Som e specime ns wcre takcn in th eearly mo rni ng , bu t th is anima] w as mo re easily loca ted aroun d1200 hours, after th c sun had burned off th c low mo rning clo uds .Duelhna n (1961: 6.58) suggcstcd th at th is species was partially noc­turnal. Sevcral snakes w ere scc ure d in cu ltiva tcd Iicld s whcre co rnwas plantcd b etwcen rock outcrop pi ngs. Others w er e loca tcd o nand under fall en logs, an d sorne were found in a rocky, grassy.agave situat ion. J. R. Dixon (pcrs. comm.) sec urc d spe cim ens from14.4 and 20.9 km \\' At enquiquc, Jali sco, un der fallen ba rk in anoa k for est b etwccn 1829-2161 m clcv a tion .

Crotalus pu sillus exh ib its a typical bchavioral pat te rn of ru ttle­snakcs from hi gh, h um id , monntain arcas. Jt wi ll olten revca l itse lfby rattling furiously when approached . bu t is com para tivc ly Icssnervous th an G. lepulu s in sim ila r enco u nte rs . :\Ian y 01' ou r speci­mcn s def ended thern selvcs vigo rously u pon discovcry, an d ofte nwould h ite thcmsclves 0 1' th e tongs w hi ch w ere uscd to ca pturethern . Rit ua lized comb at b etwcen cap tive males has beeu obse rve dby us, T he stomach of an ad ult (UT A R-4530 ) conta ine d anorthopteran.

A female collected near D os Aguas, Xlicho ac án, gave birth toon e live and four st illborn young (1\: U 155.545-54 8). and on e infertileegg on 23 january 1974 . Ran ge of varia tion is as follows : tot allen gth 165-179 mm, m ean 171; S-V ].50-162 mm , m ean 1;"5.3: w eight3.0-6.1 g, mean 4.0 . The su rv iving juvenile was maintained in cap-

44 SPECIAL PUBLICATION-!\1USEUM OF NATU RAL HISTORY

FlC . 26. C roialus pusillus . Specim en from near Dos Aguas, Sierra deCoa lcom án, Míchoac án, Mexíco. ( Photograph by John H . Tashjían .)

, ,

."

Frc . 27. Crotalus pusillus. j uveni le specimen Irom near Dos Aguas, Sierrade Coalcomán, Michoacán, Mexico. ( Photograph by [ohn H. Tashjían.)

THE NATURAL HIS TORY 0 1' ~IEXICAN RATTLES NAKES 45

FIG. 28 . Habit ar of Crotalus pusillus near Dos Aguas, Sierra de Coal com án ,Mích oac án, Mexico, j uly 19í4 . E xten sivo limestone outcropping border cd bypine-oak forcst. Snak es ap pcared more ab un da nt in arcas p revíou sly clea rcdfor cultivation , (Phot ogr aph b y [ on athan A. Campbell. )

tivity and bred , and gav e birth to thrce you ng on 15 July 1976.Two of th e young were stí llborn wi thin a singl e fetal mcmbrane,and th e mean weight au d mcasnr emeuts for both are as Iollow s:total length 111 m, S-V 98 mm, weight 1.1 g. The third neonatewas alive at birth, measured 179 mm total lcngth (156 mm S-V) andwcighcd 6.0 g (UTA H-7164).

On 24 Mnrch 1975 a pair of cnptive C. pusillus was placcd to­gether and a comp lete mating seql1 ence was observed.

1130h Male placed in cage wi th fem ale. Ferna le had prevíou sly she d anddcf ecat ed. Fem ale im mcdia tely begun twi tching.

1130-11 59 Malc began spasmo dí c forwar cl jerking ( 2 per sec ) and tengue­f1 ick ing (2 per sec) . Male loosely draped h is coils over dorsum ofIema le, bent head late rally a t 90 · an gle to longitu dinal axis of hlshod y and, b y cont racting vigoro usly, pu lled his head approxirnately2.5 cm p osteri orly along hody of fcmale. T his ac tion was perfonnedrepeat edly. Fe ma le rai scd ta íl 11 cm vertically an d oponed cloaca.Male became excited and invest iga ted Iemale's cloaca l reg íon. Thisentire se que nc e was rc pea tcd 34 tim es. Fc ma le twitch ed on lyocca sionall y.

1200 Male wra pped tai! a roun d Icmalc 's head,120 1 Maje re leased Iem alc 's hcad and hrou ght hi s cloaca to ve nt of fernalc.

Mat ing was no t accomplishe d ,1202- 1220 Both snakes rcmaíncd qu ícscent.1221 Fem ale moved head , male lost gri p and b ecarne excíted.1222-1400 Same pa tt em as above,

46 SPE CIAL PUBLICATION-\I USE U\I OF NATU RAL IlISTORY

1401 Male and fernale simulta neous ly raised ta íls vert ícally, tightlywrapped taíls. he ld position for 1 minute, th en releas ed .

1410 Female ra ised tai l verti cally ( 11 cm ) for 5 minutes. Male co n­tinued to inve stigatc .

1412 Both ma le and female raised ta i! 11 cm with cloacae juxtap osedgiving app eara nce of a lyre. Distan ce between rattle matrix ofho th snakes wa s 6 cm. Male released position , then slid tail ap­p roxímate ly 2 cm to cloaca of female. Male's tai! wa s enci rcledaround ba se of female' s tail. Male slid tai! rapidly an d repea ted lyalong longitud ina l axis of Fcm ale's ta i!.

1417 Male 's tai! enci rcle d has e of fem ale's tai! twice.1419 Male lost gri p with his tail.1·124 Fcmale raiscd tai l.¡ ·13 1 Female continued to ra ise ta i!, male insert ed right hem ipeni s. A

noticeable hulge was ap pa rent cig ht ventral sca le rows ante rior toIemale's cloaca . :-'Iale con tin ued to pu sh agaí nst rcsistance of femalewhí ch cause d the fcmale' s ta íl to bend backwards over her bod y un­ti! the ruat rix of her tai! wa s 3.5 cm above her vertebral column,

1443 Fou r quick pul sati on s at cloacal arca of male,l446 :-'Iale began undulati ons (2 per sec ) which were withi n a vertical

pla no and were 5 cm ante rior to the vent. During th ís peri od , th ema le consta ntIy pu shed th e Female 's tail hackwa rd.

1500 Male tapped men tal arr-a of his lowe r jaw in a vert ica l plan e onclorsum of Fema lc .'39 times in a G mi nut e periodo 1\0 tong ue Ilicksaccompanied thi s heh avior unl ess th e mal e shíf ted POSitiOIl .

150 9 Male ta pped his lowe r jaw on dorsu m of fem ale 17 tim es, noto ng ue flicks,

153·j Pair stiII joined , diameter of Female's cloaca was 12.5 mm whí chwas dis tended du e to ma lc's hcm ipcn ís.

17·10 Approx íma te ly 6 mm of base of hemipen is visib le.1800 Male pu shed tai l against Iemale's tail , wr ithed for 3 secon ds.183·j Same as above.1841 Bot h tail s moved slowlv for IDseco1909 Observat ions discontin~ed.

The ncxt day at 0800 hours the snakes had separated.On 22 April 1975 th c same ma le specime n was placed with a

diílerent fem ale. The samc beh avioral pattcrns were observ ed , in­cluding upraised ta ils, bending of th e Iemalc's tail ba ckwards ove rhcr body, and pulsat íons. The head tapping behavior of th e mal ewa s also obse rvcd. The rai sed tail of the female stimula ted th ema Ie no ticeab lv,

The habitat prcferrcd by C. pusillus is m íxed pine-oak forestand volca uic rack (Klauber 19.">6) and Pin e-Oak F orest at an alti­tude of 1.550 to 2300 m (D ue llman 1965),

Crotalus rub er Cope

The red diamond ra ttlesnukcs, C. ruher, of extreme southweste mCa liforn ia and adjacent Baja Ca lifornia, ar e among the largcst andgc ncrally the most placid ratrl csnakes we have observed. Partlybecausc of their range amI habitat pr cfer cllce, these snakes havebeen collec tcd by one of li S (13 LA) e\'e r)' month of th e year. Theirpeak pcriod of acti \'i ty is in lat e spring, and th e)' a re relati\'cl )'

THE NATU HAL HI STOHY OF r-IEXICAN HATTLESl':AKES 47

common through out their range. I n sou thern California, the sta tusof C. r. ruber p opu lati ons is becoming precarious as mor e and moredevelopments claim inland val ley habitats.

Crotalus ruber ruber. The northern subspecies, C. r. rub er ,ra nges fro m sou theastern Los Angeles and Orange, San Di ego ,wes te rn San Bernardino, and River side counties, and extreme south­western Imperi al County in sou thcrn Ca lifornia, south to Loreto ,Baja Ca lifornia del Sur wher e it in tergradcs wi th C. r. lucasensis(Klauber 1949a : 46). Klauber (1972: 46) also reported individualsfro m Monserrat e, San Marcos, Pond, Ángel de la Guarda, andSou th San Lo renzo islands in th e Gulf of California . It seemsreasonabl e to assume that this rattlesnake will eve ntua lly be foundon other, smaller islancls that have not ye t b een th orou ghl y ex­plor ed, It is in te resli ng to no te that a series of C. rub er , now knownas C. r. lorenzoensis, from South San Lorenzo Island in th e Unive r­sity of Co lorado collection, show tenden cies toward rattle loss(Rad clifle an d Mus lin 1975). This conclition was see n on approxi­rna te ly 50 percent of th e specimens. C . r. ruber ob ta íned by ushavo been obs erved from various locations in five cou nties in sou th ­ern Ca lifo rnia, and th e Iol lowing local it ies in Baja Californi a : 6.4km S Tij uana, the vic ini ty of Ensenada, th e H amilt on Ranch (20specime ns) ncar Co lonet, San Quintín , E l Socorro (5 specime ns),El Rosario, 16 km N Laguna Chapala, San Igna cio, 17.6 km \VSan ta H.osali a , 22.5 km S Mu leg ó. Crotalus r. ruber appears to beabsen t from the desert east of th e Sierra de ]uarez in Baja Californ iadel No rte.

In sou th ern California, C. r. ruh er is a reside nt 01' the hot inlan clva lleys which include th e Borrego D esert of San D iego County.It is Iound gene ra lly in arcas of gra nite rock ou tcroppings , espe­cí ally cluring win ter months. During th ese mon ths we have hadsuccess locati ng numbers of th ese snak es in the hott est part of th eday. They ar e oft en coiled at th e entrance of a gophe r burrow, orin th e midst of th e rubble of a dil ap ida ted barn. Harcl y are th eylocated any distance from sorne typ c of shelter. This ra t tlesnake isextremely le thargic during winter mo nth s, aneI defen sivo behavioris selclom obs crved eve n wh en it is provokcd . However, duringthe lat e spri ng and summer months, C. r. rub er becom es increasinglynoc turnal, aneI invades th e grasslancls betwcen rock outcrop s whereit probably fecc1s to a large cxtc nt on eotto nta il rabbits, Sy /r; i/ag llsaiuluboni san ctidiegi , and gr ou nd squi rre ls, Ciiellus !J . be eche ui,both of which are abundan t. In th e truc desert regions 01' its range,this snake is founcl near rocks, and seldom wanders from pro tectiveretreats. In the carly spring, pairs of red diam on d ra tt lesnakes ar eoft en observed basking tog ether in full sun light . Mating was ob­served in early April between a Iarg e pair in Railroad Canyon, justeast of Lake E Isinore, California. The snakes we re not collected .

48 SPEC IAL PUBLICATIO:\'-~I USEU~ I OF i'JAT URAL HISTORY

\Vagner (1964) ch aracterized th e vegetatíonal eharaete risties ofthe arca inhab ite d b y C. T. ruber as California Chaparral , SeasonalFo rma tion Series, and Cactus Scrub,

C rot alus ruber lue asensis. The southern subspeeies of th e reddiamond ra ttl esnake, C . T. lu casensis, has a geographic range fromth e fishi ng vill ag e of Loreto to th e Cape regi ón of Baja C ali forniad el Su r. Klauber (1972 : 46) reported specirnens of thi s ra ce fromSa nta .\ Iargari ta an d San Jo sé islands. As with C . T. T1I1Jer , C. r .lucasen sis may someday be found on other islands w hen th ey arethoroughly explore d , Specime ns ob tain ed by us fr om th e mainlandwe re co llected a t El T riu nfo, 8 km N San Jo sé del Cabo , and Bu enaVista (B. Tomherlin, pers. comm. ).

Barney T omberlí n (pe rs. comm .) reported th at C . r. lucasen siswas the most common snake in th c Cape region of Baja Cal ifornia ..\ Iost of his sna ke s w er e taken in Se pternbe r when that area re­ceí ved a major portie n of its annual ra infal l. At that time th ey w erenocturnal gcne rally, and specíme us w er e eas ily found by nigh tdriving . Altho ugh thi s rattlesnake can be found in th e deser t an dope n ari d p lai ns of sou the rn Ba ja C alifo rn ia del Sur, it is mo st corn­mo n in h eavy b rush where roc ks and rocky outcrops are pr evalent.

T h ís subspe cies inh abits th e Seaso na l Formation Series an dCactu s Scrub as defin ed by Wagn er (1964).

Cr otalus scuiu latus (Kennícott)

C rotalus scutulatus was on ce confused wi th many of the othe rpra írie d well ing rattl esnakes (Klaube r 1972: 541 ), an d th er efore,mueh th at has been wrítten abou t it may, in part, be erroneous .lt is a ra ther large, heavy-bod íed snak e th at has a rango simila r tothat of C . inolossus. Crotalu s scutulatus does no t, howev er , inhabitth e mu lt ip le habitats within íts rango as does C. m olossus. C .scutulatus is found fr om the Mojave D esert and adjacent Ne vada,sou th th rough Arizona, sou thweste rn Ne\V Xlexico, and T exas, andth ence sou th int o th e Mexican central pla tean.

C ro talus scu tu la tus scu tu latus, C rotalus s. scutulatus is a corn­mo n ra tt lesnake wi th in it s range in th e Uni ted States , Klauber(1972: 47 , 54 1) gave an excellent summ ary of the localities an dfield data for th ís race. In Mexíco, we have fou nd C. s. scutulatusthrougho ut th e Hat , arid cen tra l p lnteau , but no where did it seempart icu larly common. Snakes captured an d obs erved by us (approx.30) wer e reco rde d from : C H IHUAHUA: th e va lley between th eSierra del Nido an d Sierra de Santa Clara at 1982 m (UT A R-4554 );SOI\ORA: 12.8 a nd 17.6 km S Agua Prieta ; D URANGO: L a Zarca,12.8 km N Rodeo , Sa n Juan del Río ; N UEVO LEóN: Sa nta F e(UT A R-4.59.5), 12.8 km S Ga leana, 8 km E Sa n Roberto junction:CO AH UI LA: 3.2 km \V San Anto nio; SAN LUIS POTOSI :

THE NAT URAL HISTORY OF MEXICAN RATT LESNAKES 49

Matehuala, 4.8 km E Matehuala, ZACATECAS: 13.3 km E [une­tion of Mexican Hwy. 45 and 49 (UT A R-2715).

Miller and Stebbins (1964) not ed th at throughout th e northernportion of its range, e. s. scutulat us appeared to bc extremely noc ­tumal in behavior. Most of th e specimens ob tained by us wer e aresult of night driving. In sp ring, it was not un common to find aspe cimen coiled at th e ba se of a palo ve rde or creosote bush inearly moming. During surnrner months , how ever , these snakeswer e rarely enco un tered during dayl ight hour s. Crota lue s. scuiu­latus seems to p refer th e op cn mesqui te-creosote-cacti habitat wi thinits range. It usually avoids tru e san d desert where Ciota lus ce rastesis th e dominant rattlesnake.

In southem Arizona and adjacent Mexico, e. s. scutulaius isve ry common in prairie vallcys (1220-1.52.5 m) between th e numerousfor ested mountain ra nges of that region . Southward within theMexícan platean thi s snake becomes cre puscular due to th e hi gh erelevations of th e op en , arid hab itat. One individual obtaine d byus from grass land, ju niper pla in (1982 m eleva tion) ne ar Santa Clara,Chihuahua, wa s located crossing a d irt road at 1100 hours in early]uly. In central Duran go nea r th e town of La Zarca, e. s . scu t. ulatuswas oft en seen in mid-afternoon crossing th e highway or baskingat th e edge of th e pavernent. This ar ca is approxirnately 2440 melevation, and th e da ytimc tcrnper at u rc is somewhat cool. [uniperand grassland are th e dom in an t veg etation in th is wind-swept re­gion. Individuals from th e eastern part of San Luis Potosí, cspe ­cially around Xlatchuala, 1372 m, wer e also crepusc ula r in activi tyd espite a low er eleva tion th an at th e Durango localities. Reese(1971) found e. s. scutulatus at a locality 77.2 km S San RobertoJunction in Nuevo León , and Banta (1962) found it at CañadaHonda, Aguascali entes. One adult sna ke obtain ed by us (UT AR-4554 ) contained rodent hair.

The Temperutc Mcsquite-Crusslnnd and D esert as defined byLeopold (19.50) are typ ícal cnvironm ents for e. s. scutulatus . SeeGlo yd (1937) and Lowe (1964) for a d escription of th e habita t inArizona.

Crotalus scutulatus sal vini, C rotalus s. salc ini (F ig. 29) is alsoa resident of op en , high interior plains. It is found in Tlaxca la ,Pu ebla, and west-ccnt ral Veracruz, and its range is doubtless de­creasing as th ese pl ains are cleared for cultivat ion, The typ e 10­cality for this rac e, Huamantla, T laxcala (Klauber 1972: 147), at anelevation of ove r 2440 m, may now possibl y be devoid of enoughsuitable habitat to sus ta in a population of th ese ra tt lesnak es. AHof our spe cimens w er c coll ect ed w ith in the la va beds near Perote,Veracruz, and Tehuac án, Pu ebla (Fig. 30). Both localities supportluxuriant desert plant gro wth such as yucca, palmettos, and th egiant, slende r Neobus baum ia, which are the mos t common pl ants.

50 SPEC IAL PUBLICATION-~IUSEU~I 01" NATU RAL HISTORY

\ Vith in th e re la tive ly undisturb ed arcas of it s limited ran ge, C. s.salo ini rem a íns a ra th er cornmon sna kc . and , unlike C. s. scu tu latus,is Found in assoc ia tion wi th rocks, Thc lava beds of Perote seemto provide this rat tlesnake excellcnt hab itat. 1t ma y, howevcr, becommon th ere on ly be causc of man's cn croachment upon th e roll ­ing . ope n, rockless plains wherc C . s. saloin i was once, no doubt,th e dominant member of th e gen us . Specím ens of C. s. salc in i ob­tained b y us were '111 locat ed duriug mid-afternoon in July andAugus t, and were b asking near porou s volcanic rocks,

This ra ttlesnake is one of th e most aggress ive spccies "ve haveencouute rc d , Sev era] st ru ck so violcntly th at th eir en tire bodyappcarcd to b e momentaril y air borne. It is common beh avior forth em to strike even after bcin g constrained in clo th bags for severa]weeks. C. s. salcini inhabits th e T cmpcrate Pin e-Oak and Mcsquite­Grassland vcget ntionul ureas as defiucd b y Leop old (1950).

Crotalus steincgcri Dunn

Croialus stcinegeri is a p rimitivo rat tlcsnake Iound in th e moun­tains of sou theaste rn Sin alo a a mi sou thwes tern Dura ngo. Klaubcr(1972: 5-12) reported two spccime ns tha t ".. . werc found on th ebo rd cr of a pine for est, a t th e upper edge of a canyon di ssect ing ap la tean." i\lcDiarmid et al. (1976) reporte d an ind ivid ua l [oundon a road which was 3.3 km west of a pine forest , pr ob abl y in sub ­tro pical d ry forcst (Hard y an d ~ lcDiarmid 1969). Road tcmperatu rewas about 27°C and air tempcrature ca. 24"C whcrc th e snake wascollcc ted , A small male (UT A H-.5926) and Iemale we re collec te d atPlomosas. Sinaloa. at 1067 m on 3 Au gu st and 27 August 1976 ,res pcct ive ly, The snakcs were Iound in a trausition arca bct wcenpine-oak ami tropical deciduous for est (Fig. 4). Vegeta tio n in th isa rca includes s ílk-cotton tr eos. morning glory trecs, E nte rolob iu ni,Coccololia, nanche (B!lrsollil/la crassiiolta), cass ias , acacia s, andmimosas (Cold m a n 19.51). T he ma le wus Iou nd in a rock slidc atthe b ase of a b lu/f , an d th e female was secured in a small rodentburrow in a se mi-opo n fielcl. A large male (UTA H-6234; Fi g. 31)was foun d on 1.5 August at Eji do T cba íra , Sinaloa. a t 1067 m in atropical clcciduous for esto This individual mcasured 638 mm tot alleng th, 86 mm tai! length , ami is largor th an the largest snake re ­portcd by ~l cDiarmid et al. (1976).

Crotalus tigris Kennicott

Crotalus tigris is a m édium to small-sized desert dwelling ra ttle­snake with a proport iouutc ly small hcnd and large ra tt le. Thisspe cies has a rather limited range, ancl is kuo\Vn only frum th estates of Ari zo na a nd Sonora. Wright amI \ Vright (19.57: 1001) con­siderccl this spcc ies rareo

Cro/alus lígris is a resident of rocky foo th ills within th e Sonaran

THE NAT URAL HISTORY OF l\IE XICA N RATTLESNAKES 51

'.

»Ó,, , ,r .. _:: ~ .~., ":1..

.~ .'.- .. ,,"

FrG. 29 . Crotalu s seu / lila /lis salci ni . Spcc ímen Irorn 1.6 km E El LimonTotalco, Vera cruz, l\lexico. ( Photograph by John H . Ta shjian .)

FrG. 30 . Habitat of C rotalu s scuiulatus salcini and Sis/rurus raous, nearEl Liman Totalco, Verac ruz , M éxico. Area is lava ílow charac te rized bycactus, agav e and grasses. (Photograph by R. Terry Basey . )

52 SPECIAL PUBLICATION-~IUSEU~ I OF NATU RAL HISTORY

FIG. 31. Grata/lis st eincgeri. Specim en from Ejido Tebaira, Sinaloa,Mcxico. ( Pholograph \'r [onath an A. Cam pb ell.)

Desert of Xlexico and the United Sta tes , and rangos from near sealeve] at La Posa , Son ora, to at least 1465 m elevation (Humphrey1936). We found an individual snak e at th e same elevation on th ewestcrn slopes of the Santa Rita \Ioull tains, Arizon a. Van Den ­burgh (1922) rccorded the maximurn eleva tion for thi s spcc ies at:2440 m. C. tigris is rar ely Iound Far from rocky rct reats, Low e(1964: 173) conside red th ís ra ttlesnake to be stric tly a rock dwellerin rocky canyons, and on th e hillside s and bajadas of desert ranges.Three snakes ob tained by us from 11.2 km l\'E Scottsda le, Arizona(UTA R-6943, KU 1555:25) werc tak cn at night in early [ul y justaf te r a thunderstonn. They were active among gra nite ou tc ropswhere cacti, palo verde, and creosote were abundan t. This snakeis nocturnal and rarely ven turos Iorth before su rnmcr rains begin.Taylor (1936: 49) found two C. tigris at night, south of Hermosillo,Sono ra , coiled in isola ted rack outcro ps in low moun ta ins. \ Ve ob­served a snake of th is specics from th e Tucson Mountains, Arizona,at nig ht, as it was inves tigating a pnc k ra t nest. T his arca is veryrocky , w ith much desert vegetation. D ixon el al. (1962: 99) de­scribed th e hahitat of C. tigris in sou the m Sonora as scru b deserto

Crota lus tigr is is beh avioral ly unprcdicta ble. Two specimens[rom near Scottsda le were locat ed wh en th ey rattled as wc passedwithin 3 m of them. This observation occ urre d on an extremelywarm, hum id evening, after a thundersto rrn. A speci me n from th eTu cson Mountains never ratt led , even while bein g captured ,

THE NATURAL lIISTO RY 01" ~IEXICAN RATILESNAKES 53

Klauber (1972: 453) felt th at th is rattlesnake was generall y inoífen ­sive, and not pr one to rattle or strike.

The Seasonal Fonnation Series and Cactus Scrub as deRnecl by\Vagner (1964) are typical environments inhabited by C. tigris.

Crotalus iortugensis Van Denburgh and Slevin

Klauber (1972) characterized Tortuga Island off Baja Californiaas rocky nnd barren, more ar id than the mainland, with sparsebrush ancl cac ti. T hree specimen s of C. iortugensis obtainecl byliS (KV 174832) were coIlected on 27 Oc tober 1975 in an area oflava boulders (D. Brown, pers. comm.). \Vagner (1964) character­ized th e vegetational character of Tortuga Island as Sea sonal For­mation Seri es.

Crotalu s iranscersu s Taylor

Crotalus transoersus is, biologicaIly, a po orly known rattlesnakeboth in th e Reld and in captivity. Its type locali ty was listed bySmith and Taylor (1950) as Tres Cumbres , \ Iorclos , but Davis andSmith (1953) rcassign ecl th e type locality to nearby Lagun a Zem ­poala, J\lexico. The lat e E. IT. Taylor (pers. comm.) infonned usth at th e typ e locality ís Tres Cumbres. F urther coIlec ting mayreveal th e presence of C. irauscersu s in northwe stern Morclos andsouthwestern Di strito Fe deral du o to the top ogr aphi cal simila rityof th ese reg ions to th at of th e typ e locali ty .

Only th ree individuals of thi s species ha ve been recorded fromth e time of it s discovery in 1942 until 1971. Since the n nine speci­mens of C. transcersus havo been secu recl, síx of which are dí s­cusse d here (Figs. 32, 33).

On a tr ip to southern Mexico in th e sumrner of 1973, Charle sRadcIiffe an d on e of us (BLA) succeeded in coIlecting Iive of th esesnakes (UC\1 51421-3, KU 159361-2). An addi tional specimen wasco1Iected in May 1975 (UTA H-3988). AIl were taken at LagunaZempoala, Mexico (F ig. 34) bctween 1 August an d 5 August atelcvatious ranging from 2896 to 3293 m. The habita t w as temp erareboreal forest as deRned by Lcopold (1950). Five specimens we reobservcd basking on south-facing slopcs on volcanic rocks in th eearIy afternoo n. Non e of th e specimens was basking in di rect sun­ligh t. The snakes were found afte r morning ra in -show ers whichoccur almost daily at thi s locality du ring summer months. Airtemperat ur e at the tim e of coIlection was betw een 16-20 °C .

C. transccrsus is a very inoffensive rattlesnak e, and retreatsrather qu ickly when di scov ered . l\one of th c captive spe cimensma intaincd by us rattlcd or struck, unlikc C. t. triseriatus withwhich th ís species is sympa tric. T. \ Valkcr (pc rs. comm.) observedth at only on c of his three captive specimens ever rattled , and be­lieves that th ís species is not rar e, but is only though t to be so

54 SPECIAL PUBLICAT IO N-M USE UM OF NAT URAL HISTORY

" .

F IG . 32 . Crotalus transcersus. Specimen from near Laguna Zempoala,Mexico, Mexico. Reddish color phase with distin ct cross-bands. ( Pho togr aph byJohn 1I. Ta shjian.)

• r......

FIG. 33 . Crotalus transcersus. Specimen from nea r Lagu na Zempoala,~ I exico , Mexíco. Crayish color phase with indistinct cross-ha nds, ( Photographby j ohn H. Tas lij ían.)

THE NATURAL HISTORY OF MEXICAN RATTLES NAKES 55

F IG . 34. Habitat of Crotalus t ransc crsus and G. t riseriatus tr iscriatus nearLagu na Zcmpoala, M éxico, Mexico. Op cn fir-pin c-oak forest wi th unde rstoryof bunchgrass. ( Photogra ph by ~1. Cranger.)

56 SPEC IAL PUBLICATIO:-.r-~1USEU}, 1 OF 0iATURAL IlISTORY

because of its limited ac tivity periods in its natural ha bitat. Anabundance of lizards und mice in th e preferred hab íta t of C. trans­versus probab ly results in the need Eor only limited forag ing ac­tivity. Klauber (l9í2) men tion ed that one individual conta inedlízard scales, and one of our snakes defecated l ízard scales, probablySce loporus ae ne us.

A nu mb er of Food items were offcrcd to captive C. tra nsoersu s:treefrogs (HUla), Iízards (Sceloporus, Ce rrhonotus, Uta, Plujllo­dacuj lus, Xantusia, Cnemidophorus, Anolis}, wild rodents (Musmusculus], snakes (Thamnophis, Nerodia), newborn laborato ry ra ts,sparrows, and domesti c gray crickets (C rijllus) : all were refused .The rodents we re kill ed by the snakes , but th e other potential preyitems were ignor ed .

Captive snakes of this species were maintained by us at th eFollowing th ennal Ievels: (1) 26.5°C during th e day and dr oppí ngto 10°C at night; (2) 2.5-27°C during th e day, 20°C at night; (3) low20°C tempcrature at all tim es. Thcsc sna kes may have b ecn affectedby th e change in eleva tion from their nativo habi ta r to captive con­ditions. They fared badly at all three thermal levels.

C rotalus triseriatus (Wagler)

The dusky ra tt lesn akes of south-central Mexíco are, taxo nomic­ally, on e of th e most complícated groups of rattlesnakes ye t de ­scribed. \Ve ha ve mad e ove r 100 obse rvations of both subspecies,and thi s field work has shed som e light on th eir relationsh íps. Ithas becorne apparen t to us th at th e two curren tIy recognized sub­specíes, C. t. tr iseriatus und C. t. aquilus, requ ire a complete review,and suc h work is underway by several of our colleagues .

Crotalu s triseriatus tri se ria tu s. Crota lus t. trtser iatus is a mon­ta ne race reaching the highest altitude (4572 m on Mt . Ori zab a,Veracruz) at wh ich any member of th e genus Crota lus has beenreco rded (Klauber 1972: 516, 542). Although Eound at such highalti tudes , C. t . triser iatu s is mo re commonly encoun tered at eleva­tions betw ecn 2743 m and 3353 m. Specimens have been recordcdby us from : JALISCO: th e mountain valleys N Nevado de Colima(UTA 1\-4909) (see Campbell , 1979); \ IEX ICO: Laguna Zempoala;D IST HITO FEDERAL: La Cima; t\IO RELOS: Tres Cumbres,th e lava be ds N Cu ernavaca , Huitzilac (Fig. 35).

Crotalus t. triseriatus probably occurs in th e Mexica n state ofPue bla, bu t we have no records as yet from that ar ca , It also maybe Iouud on Cerro La Malin ch e, a 4267 m peak in Tlaxcala , Resi­dents in this area describ ed to us a snake wh ích appeared to beC. t. triser íatus, but no specime ns have be en secu red. In general,the range of C. t . triseriatus follows a narrow east-we st belt be­tween the 18t h an d 20th parallels. This range includes CordilleraVolcánica oE souther n Mexíco,

TH E i\'ATU RAL HISTO RY OF ~IEXICA :--J RATTLESNAKES 57

Crotalus t. triseriatus is one of th e mo st common fonns of th esmall Mexícan montano rattlesnak cs. Due to th e high clevationsat which it occurs, thí s subs pccies is almost entirely diurnal inactivity . Evcn during th e wa rmer months of th e year, temp eraturesfall to levels a t nig h t wh ích would no t permit ac tivi ty by this snake.Consequently, th is rattlesnakc is mos t easily obs erved in morn ingsand aftc rnoo ns when th c sun has sufficic nt ly warm ed its habitat.Thcse animals are also active during th e rainy season, and it isnot un common to find severa] Iollowing an afternoon showe r, bask­ing on rocks th at are still warm from th e carl icr ra ys of th e sun .Dav ís and Smith (1953: 141) found C. t . tr ise riat us common nearHuitzilac, Morclos , along streams th at wcre bordered by a luxu ríantgrowth of bunch grass. Ou r observntions agrcc with th círs, this-snake is rarel y found any dista ncc from a ro cky, grassy envire n­mcnt. \Ve have obtaincd snakes on rock slide s near Laguna Zem ­poala, Mexico , but they are not nca r ly so common th er e. Duellman(1965) m cnt íoncd thí s spccics as an inh ab itan t of th e Pine-OakForcst at 1600-3270 m altitudes.

Crotalus t. triseriatus exhí bits beliavior tha t is comparab le toth at of othcr rattlesn akes in montan e habitat s. lt ís alert and readyto retrcat whcn annoyed , yet cur ious cnough to expose itself tocapture, This subspccies is rcla tivc ly u naggr essíve evcn when be­ing capture d. \ Vc havc obscrved ritual ízed comb ar b etweencaptive males. C. t . iriseriatus fccds on lizards and sm all rodents

FrG. 35. H a bitar of Grata/lis t riscriatus triseriatus and Sistrllrlls racuc.La Cima , Dist rito Fed eral, Mexico . Old lava Ilow covered with bunch grass,Iormerly a pine forest. ( Photograph by ~ 1. Gr anger.)

58 SPECIAL PUBLICATIO~-~lUSEUI\ 1 0 1' NATU RAL HISTORY

which are pl entifu l in its preferred habitar. Cursory examination ofstoo ls from Freshl y caught specime ns supports th is diet prefer ence.

011 15 july 1970, a female from the northern drai nage of Nevadode Colima, ] alisco, wa s loca ted in a partia lly cIeared píne-oakforest under a log, along with six new- born young. A captivefemale pas sed a part íally formed embryo on 1 ]uly 1976. Fouryoung were born on 30 Oct ober 1975 to a ca ptive Iernale collec tedat La guna Zempoala . Hange of variatio n is as follows : total length1.59-178 mm , mean 168; S-V 141-161 mm, mean 150; weight 4.8­5.1 g, mean 4.9, A ca p tive pair was obs erved in copulo on 24 A pril1975 at 0800 and were separated at 1400. The sam e pair also b redon 8 Septe mber 1977.

Crotn lus tri seriatus aquilus . Thc northern subspecies of thisrattlesnake, C. t. aq uilu s (Figs. 36, 37), does not reach the highaltitu des inh abited by C. t. t ri seriat us. lt seems to prefer the open,grassy hab itat s north of the Co rdi llera Volcánica. Specimens as­signable to th is subs pecie s havo been recorded by us fro m:~llCHOAC:\N : 16 km w Jiquilpall ; SAN L UIS POTOSÍ : th evic inity of Alvarez ; HIDALCO: ]acala , San Vicente, D ura ngo, ElChico (KV 1.55549-553, 1555.56; UTA 1'-4.540, 6941), La Estanzuela(UTA R-4675, 6115).

This rattlesnake is a co rn mon montane snake, but. as previouslystate d, docs not usually occur in extremely high-a lt itude habitat s.Klauber (197:2: .517) gave 2438 m eleva tíou, nea r Jacala , Hidalgo,

• ..

...

.-,

,.

"

" . ... ."

Ot o , ~• .,. •

, ,

:..; -.. .-. ,

\ ' . ..\.....

. .. .. ... .. . ......Frc . 36. Crotalu s triseriatu s aqu ilus. [u veu ile specimen from near El

Chico, Hidalgo, M éxico. ( Pho tograph by [ohn H . Ta shjian.)

THE NATURAL HI STORY OF ~ I EXICAN RATTLESNAKES 59

.'.• . ;

1'1(; . 37. Cro talus triseriatu s aq uilus. Specimen from near El Chico,Hidalgo, Mexico. ( Photograph by [oh n 1I. Tas hjian.)

as th e h igh est point w here G. t . af/ IIí/IIS has been co llec ted . II ow­eve r, we ha vo locatcd a pop ulat ion nea r E l Chico, Hidal go (F ig .38) w her c th ese rat tlesn ak cs have hcen foumI up to 3110 m in afir forest. The snakes from th is popula tion, while fal\ing wcll wi thi nth e known ge og ra phic range 01' C. t . aquilus, are quite t1ifferen tfrom 0\11' othe r specime ns of this racc, T hc y are largor and exhib ita gr eenish hu e, with males far excccdíng Jemales in size andb rig htn ess of color. Thcse spec imeus tcnd to be hcavier borliedthan typica l G. t. aquilus and th ey ar e extrcmely a lert an d ag­gress ive . In many cha ra ctc rís tics th ey rcs ein bl e G. lcpid us. Fu rt he rstudy 01' th cse sp ecim en s is necd cd in arder to uu ders tand th cirstatus in relation to other popul at io ns of G. t . aq uilus.

C enerally, G. t. aq uilus is an inhahi tan t 01' pinc-oa k forests andopc n mcsqu ite-g rasslands 01' the southe rn cen tra l Mexican p la tcau(Fig . 39). Snak es from Mi ch ouc án, the sou the rnmost po rtien of th em uge of G. t. aq uilus, u sua lly inha bi t mes quí te -grass lnnd. No rt h­ward to Hidal go and San Luis Potosí, thi s race tends to occurmore commonly in th e pine-oak fo rcs ts whc re th ere is an ab unda nccof rack outc roppings .

The behavíor of G. t. aquilus in tite Iicld is much th e sume asth at of G. t . triser íatus, but individuals of th e form er teu d to hesome what more aggressive and casi ly ng ita ted . These sunkes oftenreveal th eir presence by rattling wh en alarmed, as is typical of

60 SPEClA L PU BLICATION - MUSE UM OF KATURAL HI STORY

FIG , 38 . Habi ta t of Crotalus t riseriatus aquilus, nea r El Chico, Hid algo,Xlexico. Fir Iorests cove r hills rea chíng elevations exceedí ng 3 110 m. Snakesmost commonly found in open roc ky outcrops, ( Photogra ph by j onathan A.Carnp bell. )

FIG, 39, l Iabitat of Crotalus triseriatus aquilus, near San Vicen te , Hidalg o,~ [ exico . Stcc p hillsides are cove rcd with pin e-oak foresto Snakes most corn­mon in ope n limeston e bedrock. ( Pho togra ph by H. T erry Basey.)

THE NATURAL B ISTORY or ~IEXICAN RATT LESNAKES 61

e. le pltlu s. This race is active in th e momings und afte rn oons, butunl íkc e. t. triseriatus, it mu y be Iound foraging at night. \ Ve h avefound them while dri vin g at night in th e vicinity of Duran go ,Hidalgo , a somewhat humic1 ar ca wher e night temperatu res areoccasionalIy fa vorable fo r activity. Ritualized combat b etw eencaptive males has been obscrve d b y uso

Two Icmales of e. t. aq uilus Irom El Chico, Hic1algo, gavebi rth to six and seven young on 7 [une 1974 anel 29 [uly 1974, re ­spectively. Range of va ria tion of th e two brood s is as follows:total lengt h 168-192 mm, mean 178; S-V 1.53-177 mm , mean 163 ;weight 5.0 -8.8 g, mean 6.4. Anothcr female, collecte c1 16 km \V[ íquilpan, Michoac án, ga ve birth to threc young on 29 June 1974.Ran gc of va riat íon is as foIlo w s: tot al length 164-171 m m, m ean167; S-V 1.50-156 mm , mean 1.52; w eight .5.0-6.4 g, mean 5.5. Acap tive pair of e. t. aquilus From El Chico was observec1 copula tingon 28 April 197.5. One of these snak es later gave b ir th to twovia ble and on e c1eformec1 young on 27 [ uly 1977, an d the measure­me nts anel weights ar e as foIlows: total Iength 120-181 mm, mean1.50; weig ht 4.9-7. 8 g, mea n 6.3. T he d cform ed snake exh ib itcc1 afusio n of th e ventral surfacc in th e low er cervica l ar ca (UT A R­6940). Ano ther pair of e. t. aq ui lus wa s joinec1 in mating at 0830hou rs 011 26 October 1977. The Icmalc's cloaca was disten ded an dth e male's boc1y pulsatec1 (twice pcr SeCOl}(!) ncar th c ve nt c1uringcoi tus . The uplifted tails of th e snakes produccd a ve ntc r-to-vente rconfiguration in th e region of th c cloac a. Separatiou occurrecl at0901 , and detumescen ce of th e hemipeni s oc cupied 7 SCcOllC!S.

D ucllman (HJ6.5) charactc riz ccl the vegctntion al cha rac te r of thehabitat of thi s rattlcsnake as ~ lesf[uit e -Grassland and Pine-OakForcst at 1600-2000111 altitudes. This racc is found in th c TcmperateMcsq uite-C rassland and Pine-Oak Forest as defined b y Lcopold(19.50).

Crotalus virid is (Hnfiucs que)

Crotalus viridis caliginis. Cro tulu s v. caliginis is a ra cc [oundon Sou th Coronad o I sland off th c northwcst coa st of Baja Cali­foruía . This arca is roc kv with hrush ami cac ti, a nd two adultspcc ime ns (KV 1748.35, u'TA 1\-694,5) w cr e collectc d at th c northend of th e island on 2.5-26june 1D76 (D. Brown, p ers. COIl1I11.). Thefemale passcd one partiall y fonn ed cmbryo on 14 Augnst 1976.

This subspccies is found in the Ca lifornia Chaparral as defin edby Wagn cr (1964).

C rotalus viridis hell eri . Crotalus v . hclle ri is a subspccics foundin sou the rn Californ ia and nort hcrn Baja California, und is a resi­dcnt of almost every hab ita t wi thin its range. As with e rub er,with which it shures a great dcal of its range, a numher of e. v.lielleri ha ve [icen observed by lIS every month of th e ye ar. These

62 SPECIAL PUBLICATION-~IUSE UI\I 01' NATU HAL HI STOHY

snakes vary greatly in color a nd pattern within a give n population .As ind ividuals 01' th is ra ttlcs na ke age, th ey appa rently lose th eirpattern 01' it fades g reat ly, a co mmon t ra it 01' all races 01' C . oiru lis.Mos t la rgor specimens 01' C . v. hcllcri are hlack 01' very durk withlitt le pn t tcrn, Many young 01' thi s race have d ístinctl y patternedheads, but thi s fades a t an ag e 01' two ycars ou most individuals.

C. v. liclleri ranges from San Lu is Obispo and Kern coun t íessouth th rou gh southern California (avoicling on ly th e true desertsin th e eas te rn part 01' th e state) aud con tinues into Baja Californiaas Iar south as Playa .\I aría Ba1' on th e w est coas t, a nd ncar Bahíade Los Ángeles on th e eas t coast (Klaub er 1949b : 8.3). Xlurray(19.'5.'5 : 47) reported a specimcn 3:2 km SE Mcsquital , sorne 88 kmsouth 01' Klauber's (1949h: 83) sou thcrumos t record. Sm ith e t al .(1971) Found two spee imens 69 km \\'i\'W Bah ía de Los Ánge lesanel 16 km S E l Arco. Specimens [rom th ese southc rn mos t locationsar e rare, altho ug h it is possihl e for C. v . liclleri to inlia h ít th e ar caas Ia r south as San Ign acio in ce ntral Baja Califo rn ia . Hattlesnakesob tained b y us come fro m many localiti es in southern Californ ia,but we ha ve Few records from Baja Califo rnia . Individual speci­mens from ~ lexico ha ve hccn observc d Irom Pun ta Camalú, north01' En senada, an d th e westem slopcs a nd int erior peaks within th eSierra Juárez.

C rota lus v. hcllcr i is couun on within its range, althou gh itsnum bers seem to dccreasc in th e southe rn portion s. On th e 10\Verslope s 01' th e San Gabrie l Mount a ins in Los Ang eles Co un ty, Cali ­fornia, the populations 01' this race a re as co nccu tra tcd as any 01'th e genlls known to us . Thi s is a rugged, rock y arca with chaparral,and th e ra íny seasou occurs in th c wiuter an d early sp ring. Hatt le ­snakes havc hcen Iound fro m th e edges of th e Sa n Ga briel Hive rto th e hot , sparscly vcgetatcd , south -Iucing slopcs a nd pine-oakslope s facíll g th e north. Altho ugh ind ivid uals of C. v. liellcri in thi sa rca do not de n 01' hiberna te as suc h, th ey do co ng reg atc in rockslides 01' rock outc rops which [ace th e sou th 01' eas t during rain)',winter mon ths. '1'0 the sou th in Or.mge, Hive rside, and San Diegocounties. thi s subspecics is Iou ud from th e Pacific coast in rolli ng,g rassy savannahs to at least 3200 JI} in a pine-fir forest 011 '\[ t. Sa nJac into. Throughout mos t of thc se southe rn California counties,C . initclielli ¡JUrrlllls anel C. r. T111Jcr live sym pa tr icnl lv wi th C. v.llelleri . \Ve have observed a l1 three ra tt Icsnakes wi th in 45 m ofcaeh other near \ Varner Bot Springs, jusl 1I0rlh 01' th e BorregoD esert. 111 lhat particular ar ca , all three species sepm eq ua ll1'ab un da nt. Elevalion in th is arca is approximalel1' 1068-1:220 m.111 1967 oue 01' us (BLA) found a n appare nt h1'hrid , C. v. helleri X C.r. mber, on lh e road in th is s:lIne ge nera l arca . Hep orts of hybridsfronl thi s a rca are nol 1II1COIllnHlIl.

In Baja California, C . v. ' IClleri is Illllch less com ll1on amI is

THE NATU RAL HI STOHY 01" },IEXICA0: RATT LES0:AKES 63

apparently rc p laccd b y e. c iujo [urcu s, e. r . ruber, and e. mitcliellipijrrhus. A snake Irom C am ul ú was observed in sc ru b by, coasta lvege tation approximatcl y 9 m Irom th e sho re line . Ano th e r exam plefrom th e w est ern slopes of th e Sierra ju árez w as Io und b askin g indiffused su nligh t unde r a manzanita b ush, Klauber (1949b : 83 ) re­ported a sp ecimen 16 km 1\'W Ba h ía d e Los A nge les in desertmountaius in an eleph an t trec association.

Crotalu s v. he llcri tends to be a ra ther aggressi\'e Io nn and iscas ily agitated, b ch avio r reportcd b y Kl a uber (197:2: 454 ). Mostadu lts wi ll dcfend th emsel ves vigoro usly,

\ Vagn er (1964) cha racte rizcd Ihe vegcta tional charactcr of th ehabitut of e. v. liel lc ri as Cu lifornin C haparral and Xlont an e For­matíon Series, und Leopold (19.')0 ) cha racte rizeel it as Pinc-O ukWood lund nnd Piñon-jun ip er \ Vooellanel.

Crotalus icillarili Xleek

T he ridgenose ra t tl esn uke. e. icillard i, is an exa ru p le of a sm ull,montano spec ies whose hiol ogy has rcmaincd some wh at obscure,))0 doubt due to difficulties c uc ou ntc rc d in reach ing possihl e Xlexi­ca n collcction lo caliti es. Littl e is know n of its h uhi ts, hu t it eloesno t appear to b e rare w íth in its rauge. Th e four raccs 01' thi s spe­cíes co llec tive ly in habit th e Sie rra .\I aelre O ccid en ta l Irom south ­easte rn Ari zona aud so n thwcst crn 1\0 \\ ' ~ Iexico, southeas tc rlv tosouthcm Durango and w es tc ru Z aca tccas (Kla ub e r 1919c : U .5).

Crotalus w illur d í w il lardi , T he northern su bspccies. e. le.ic illardi , is a resident of th e pine-oa k Io n -st s of the l Iu uchuca andSan ta Hita Xlountains in Ari zouu, a nd th e Sierra de Ajos and CerroAzul in So no ra , Xlexíco. T hi s ra tt lesnakc scems to pn -fc r th e morehum íd ca uyo n bottoms of pin e-o ak habitats as opposed to ex pose darid slopes w here e. lepulus ami e. pricci are conuuon . B. Toruber­lin and H. T . Basey (pcrs . COU lIl!. ) rr-portcd that iud ivid ua ls Iromthc Sierra ele Ajos (UT A H-66S9, H-GB:2S-30 ) w erc co nu no n in th cwide, rock y st rc am beds w hcrc po ol s o f w at er remained a fter su m­mer rains. This was between HJS2 ni uud 2287 m in e lcva tion, '1''''0lizurds (ScclapaTl/s jarrad and S. uiululatusí were cornm on in thi sstrc um hed hahitat. and no do uht co nt ribu te a ma jo r portien toth e di ct of thi s snake. Kl au bc r (1972: 61:2) mentioncd a spccinu-nth a t conta inc d a bru sh mousc (Pcronujscus ho uli}. Alt ho ugh prc­fcrring th e coo le r, hu m id cnnyons, e. w. willard i is in no \\ ' a ~ ' re ­strided to this habitat. A sna kc from upper .\I ade ra Callyon a t2593 m in the Sa nta Rita .\ \ollntains w as obs erveo on an eas t-faci ngslop e amidst brok en ro ck a nd sc m b oak . It ",ould llave b een O\'cr­looked hao it not ra tt led , fo r lil e a rca ",he re it was foumI is steepamI th e sc m b oak nearly impenetrable . A spec imen of e. pricei\Vas locatcd nearb\' . e. IV. Icillan li is nlos t acti\'c on \\',lI'm , humiddays whcn th e sl;nlight is in tcnn itl en t. It is es pecially COllllllon

64 SPECIA L PUBLICATIOl\ -~lUSEU},1 OF NATURAL HISTORY

befare aneI af ter an aíte m oo n shower when the temperature ishe tween 24-29 °C .

Crotalus lV. icillardi is typica l of th e small, montane rattlesnakesin tha t it is nervous an d irri table, although not to th e degree ex­hihited bv C . lepid us or C. pri cei . At times it reve als its presenceb y ra ttling, and wí ll cru wl to sa fe ty upon th e 1cast provocation.Captured spec ímcns a re more apt to turn and hite , as opposcd totypical ratt les nake stri kiug behavior. Kaufleld (1943b : 3.57) aneIStehhins (19.54: 484) aIso found this to h e true. Aft er a shor t periodof time, captivc spccim ens of C. lV . icillardi gen er all y calm downaud main tain a peacef ul d isposi tío n.

Ma rt ín (197.5'1, 197,5h) di scu ssed reproduction in C. te . ioillardi.011 18 Apri l 1971 a cap tíve puir w as observe d b y u s in capillo atOSOO hours, and they wcrc stil\ join ed at 1700 hours when obse rva­tions were discon tinucd. T here wcrc no res ults fro m thi s mating.

Crotalus le. icillardi is fonn d in th e Xlon ta ne Formation Seri esami Xlontanc T h ieke t as defined by W agner (1964) and Pine-OakForest and Pine-Oak Woodland as dcíincd b y Leopold (19.50). :SeeC loy d (1837 ) ancl Lowc (1964) for a clcscri p tion of th e habitat inAri zona.

Crotalus w illurd i amab ilis. Fin adult (K V 178794 ; Fig. 40)a ncI Iou r su hadult C. te . amahihs (UT A H.-7162) were taken inArroyo Meste ño. Sierra del N ido , C hi huah ua, a t 2440 m 011 18, 19,21 JI'tly 1877 (L. A. Xl ítche ll aud D . G. Barker, pers. comm.). Mostof the snakes were loeat ed a t th e bases of small tr ees in pil es oftwigs and lea f litt er ncar strearns , one was Iound in a sh in-oakassociation , The arca liad bcen logged three times in twelve ye ars,ami the las t Iogging hacl occurrcd four ycars ea rlier. Al! snakcswcre vis ib le , sorn e coi Ied am i others crawling , and only two rattledw hcn captu red. Int erm itt ent thund er storm ac tivity had oecurredfor two weeks prior to 18 Jul y, and oeeasional showers oeeurredduring the collceting period. T he ambien t temperatu re was ca.21 °C, und the snakes were foune! throughout th e day. T\Vo C. p.pri cei , 011 e wirhin .5 m of an C . IV. am ob ilis, and two C. Iepidusklouberí, one in seruh-oak '1]](1 th e other in a talus slope near shin­oak , werc also foun d . Two C. te . atnahi lis defeeat ed rodent hair inth e Iaboratorv. H. K. Cuese (pers. eomm.) obs erve d a ca ptive mal eeourting a fem ale on 8-9 September 1977 . The Iemale rernaincdin a resting coi l and th e malc direete e! head-bohbing and tongue­f1i cking across the fema le's do rsum (3-.5/.5 seconds ). The malemoved his uplifted tai l in hoth a hori zontal amI vertical pl an e witha n lIndlllati1lg mo tion , Physieal co nta d w ith th e side of the en­c10sure or th e sllhstra te stillllllatc d this hehavior whieh \Ve interpretas TaiJ Seareh Copu latory At te lllp ts. The seq ue nee la sted .5 minutes.

Crota lu s w illar d i Illcridionalis . The sOllthermn ost sllbs peeies,C . le. Ill cridiollalis, inhabi ts a lim it ed area in southern Dumngo amI

TIlE l'iATU RAL HISTORY OF },IEXI CAN R.ATTLESNAKES 65

extre me sou thwe ste rn Zncatec as, ano few specim ens are ava ila blefor study (C loyd 1940; Klauber 19(2). Like its siste r mees, C. tO .

merulionulis is a montan c inhub itnnt ra rc ly Iouncl below 2440 m .This subspecics is not genera lly a canyon -bo ttom dwell er. T hearca inhabitcd b y it is hi gh (2440 m) pine-cover ed pl ateau s whereop en mcadows previd o breaks in th e foresto Five individual s ob ­tain ed by us from near Llano Grande, Duran go (F ig. 23; UTAR-5639-41, 6124-2.5), wc re co llec tc d on 4 Aug ust 1975 on a partiallyopcn hillsid e which slopcd into a g ra ssy meadow. The slope hada northern to northeastern exposllre . AII specimens were loca tedat ca. 2.560 III a t a tcmp cra tur e of 21-24°C betw cen 0830 an d 1000hours . 1t liad ra íned th e previou s evcuing a nd contin uc d until0600 whcn th e sun appcared. The cnviro nme nt was h u rn id w henth e rattlesnakes wcre ca p tu rcd , an d none was found a fte r th e h ighclouds liad disappcared . The hab ita r, alt ho ug h no t a canyon , wassimila r to th at oc cupied by othcr ra ces of C. u.illurtl i. It was com ­posed of sparse short-needle d pines mi xed w íth eq ually sparse oa kand madro ño. Rock s wer e scat ter ccl throughout the scrub-oak, andgrassy g ro llmI cover p rovid cd cxc ellcn t retreats. AII five specime nsw ere ncwborn YOllllg and had sh ee! their skin at Icast on ce. Theyexh ib itc d gClltle di sp ositions and re fusc d to bite upon cap ture . A1Iadu lt mal e C . ti; . mcridionulis was [ound 011 18 [ uly 1976 a t th eeres t of a partiall y dcnudcd hill with a Iow den se covc ring ofscruhby brush . It was hasking in d ircct sunligh t at 1100 hours. Anadult female, opaqu e-col orcd pri or to shcdd ing, was discovercd at

Fic . 40. Cro /U/IIS usiltardi amahilis. Specimen from Arroyo Meste ño, Sie rradel Nido , Chi huahua, Mexico. ( Photograph by Jonath an A. Campbell.)

66 SPECIAL PUBLICATION-~IUSEUl\ 1 OF NATU RAL HISTORY

1000 ho urs on 12 Jul y 1977 during an intermittent ra instonn. Hea vyfog sh roud ed the ar ea in th e ea rly morning. The ambient tempera­ture wa s ca. 21°C , an d the snake was resting in sha de. Seven addi­tionaI sna kcs (one preservcd , KU 178975) we rc taken in th e upperreg íons of th e mountains at a ranch near th e city of Durango (S.Prchal , pers . cornm.) .

Th ís snake inhabits th e Montano Fon nat ion Series as defined by\Vagner (1964).

C rota Ius will ardi silus. C rotalus w. s ilus (Fig. 41) is aIso a resi­den t of the temperat e, p ine-ouk for ests in th e Anima s Mountainsof Ne\V :\l exico (Bogert and Degenhardt 1961), th e adjacent Sierrade San Luis, the Sierra de la Purica (Sierra de Nacozari) in Sonora,an d th e mo unta ins to th e immediate eas t and sou th of Chihuahua(Fig. 42). C rota lus w. silus is ver)' similar to C. w. ioillardt in its·habi tat prcfcrence. Snak es from th e Animas an d San Lu is ra nges ,howcver, cxist in a much drier climate since th ese mountains re­ceive less ra infaIl than mountain s which support o ther C. w illard ipopulations. Three indivídu als observed by us in th e AnimasMountai ns we re founcl in lat e Octob er and earIy May whe n it wasvery dry. AH th ree specimcns werc located at an elcvation of 2120m on east-faci ng sIopes where pi nes, scrub oak, and manzanitacomp rised th e major vegetation . No ne of th e snakes rattIed ortried to escape , nnlike other C. w. silus from humid habitats.

\ Ve observ ed approxima tely 40 C. w. si/us bet:ween 1970 and1974 in the Sierra de la Pur ica in northem Sonora (KU 155554-555,

,.

FrG. 41. Crotalus willardi si/uso Specim en from Sierra de Nacozari, Sonora,~Iexico. ( Photcgraph by [ohn 11. Tashjian .)

THE NATUR.AL HI STO RY 0 1" ~1EXICAN RATTLESNAKES 67

158562, UTA R-6942). No other member of th e genus has beenobservcd in thi s rangc, which contains perfect C. icillan]! habitatconsisti ng of lon g, large canyons with a south to north strcam-Ilowwher e wate r is present th rou ghout th e yeaL Pines and oaks dorni ­nate th e vegetation wi th syca morcs in stands along th e wide can­yons. F ems and poison oak provide ground co ver in th e rockystream beds, where C. IV . silus is mo st prevalent . Snakcs have beensee n from April throu gh October , with th e greates t uumbers beingobse rvc d in th e [ uly-Au gust ruiuy scason , At th is time. gcn eral lycloudy skies and high hu midi ty provide excelle nt cou di tio us forthese snakes. On on e morni ng in carly Jul y wc obs ervcd ele venspecimc ns in a two hour pc riocl while hiking in a single cauyon atelcvations of 1630 111 to 2300 11 1. Xlost of the suakcs appcarcd tobe foragillg , since only on e of the eleve n wa s observed in a coiled ,basking position . Of th e four xpecimc ns coll ected that morning ,on e g ra vid fem ale gavc hirth to Iive viab le young on 7 Augu st 1970.Another contained four fully clcv elop cd emb ryos.

Ten females and one male w ere observcd in the Sierra de laPurica betwecn 15-2.3 [ ul y 1978. One pair was copuluting on 15[ul y, and two adult femal es appcarcd as though th ey had just givenbirth. Auothcr female gave b irth to [our young ( ~ U 179025) on10 Augu st 1978. Total len gth of th e Iour ranged from 146-218 mm,mean 190; S-V 129-193 mm, mean 160; weight 4.9-6.9 g, mean 6.0.

FIG. 42 . Sierra de la Pur ica ( Sierra de Nacozari }, Son ora , M éxico. H abit atof Crota lus icillardi silus. C an yon bol tom s ru n sou th to nor th , pine-oa k fo restwi th Ie rns , poison oa k, syca more tr ees. Aspcns in up pe r regi ous. ( Photographby H. T erry Basey. )

68 SPECIAL PUBLICATION-~IUSEU},I OF NATU RAL HISTORY

On 17 April 1971, captive breeding was observe d, The femalewas placed with th e male a t OSOO hours. The male appearecl torecogni ze th e presence of the female w ithin 10 seconds , b egantwitchi ng (1 twitch pcr second), and tes ted the en ti re dorsal surfaceof Fcmalc's body with his tonguc (2 tongue-flicks per seconcl). Them ale rubbed alon g th e dorsal surface of th e female for approxí­matel y 5 mi nutes by ho lding his h ead at 30 ° angle and sl íding th earc a of th e mental scale Iorward for 1 cm. O ther mating d atesrecordcd were 19 Apri l 1971 and 29 [ anuary 197.3. T he ma tingswere u nsu ccessful.

An interesting observatiou was made b y us concerni ng thebrown colora tion of indivídu als of C. le. silus from the Sie rra elela Purica , Those specimc ns colle c tcel or observed aboye th e wa te r­falls (2070 m) tended to bc ligh t b row n, rcsem bling th e dominantpine nccdle littcr. Othcr specimens frorn below the waterfallstended to he a much dark cr brown, rescmbli ng th e more dominantoak lcaf littcr. Sp ecimcn sizc was apparently no t a fac tor in thisdifferen ce in color.

Sistrurus raüllS (Cope)

Sistruru s racus is a resid eut of the tablelancl of sou th-cen tralMexico. lt occurs in a variety of habitats wi thin that tablcla nd,rang ing from ncarly 3050 JII in pine-oak forcs t near Huitzilac,Xlorclos, to about 1525 111 in agavc-cacti habitat of the va lleyswhich surround th e cíty of Oaxaca in central Oaxaca , Specimenshave been recorded b y us from : P UEl3LA: Zacapoaxtl a, Cacaloa­pan, Pu ebla (J. A. Campbel l, pers. comm.), T LAXCALA: near Sa nD ion isio; DISTR ITO FEDERAL: La Cima; :\lORELOS: I-Iuitzilac,th e la va b eds north of C uc rnav aca ; OAXACA: near Mirla, Ixtl ánde Ju ár ez .

\ Vithí n it s known range, S. racus is a very common ra ttlcs na ke .It see ms to be rather gregarious, a t least in mountain va lley habitats.\Ve have observcd over 100 S. racus under mauy vnried cond itio ns ,a nd it appears to b e a ver y adaptable sp eci es . For cxample, nearHui tzilac, Mor clo s, a largo for ested area had bcen clcared , perhaps30 years ago , and no", consists of taIl b unch grass (Fig. 43). SistrurusTa üllS ha s occupied thi s ar ea and has become so common th at thelocal peoplc ar e extremc ly awnrc of its prcsence. The populationfrom th is parti cular ar ca (at an clevatiou of 2866 m) conta ins thelar gest examples of thi s snake of aIl the localiti es whcre we havocollccted th cm . Several males measured 76 cm and engaged inritualizc d combat in ca p tivity. Many of these males ten d to b emc lanistic, a characte ristic that Klauber (1952: 114) notcd in thcsesnakes from T res Cumb res, Mor elos.

Al tho ug h S. Taü llS scc ms to prcfcr grassy mountnin val leys , it

TIIE NAT URAL llISTORY 0 1' ~ I EXICAN RATTLESi\'AKES 69

is not restrictccl to th at habitnt . It is com mon in th e lava bed s northof Cu cmavaca, Morclos, where it is sympatric with C. t. t riseriatusand C. uiolossu s nigrescens . S. ra GllS from this arca are muc h sma llerth an the Huitzilac specim en s. I n parts of Pu eb la, Vera cru z, andadjaccnt Oaxaca, S. racu s is foun d a t lower elcvations in arc as ofgrass, agaves, cacti, and small, stuntcd oaks (Fig. 30). I ndividualsin thi s h ábitat appcar to be more dispersed and were encounte re dless frequcntly.

In th e spring of 1974, Jona than A. Campbe ll and one of us (BLA)located an un rcp orted disjun ct pop ulati ou of Sist r u rus in th e centralhighlands of Guerrero. This populati on is removed sorne 330 airkilom eters from th e ran go of S. rm)llS as plottcd by Klauber (1956:58; 1972: 64), and is isolntcd fro m othe r popula tions by the RioBalsas basin to th e north and th e Chilpancingo gap to the east.A complete descr iption of th is Cuerreran pop ulat íon is for thc om­ing (Camphe ll and Annst rong, HJ79). However, we think it properto describ e here th e habitar and habits of these snak es. Theyar e resid ents of th e piue-oak forests of th e Sierra Madre del Sur,and all of our specimc ns were scc ured in largo, brushy Ilood plain sat vur ious eleva tions bet wccn 29í5-3105 m. The first sna kcs wcresecurcd in mi tl-M ay during th e warmer parts of th e day. This re ­gion receives ca. 1500 mm of rai nfull from ~ Iay through Octob er(Page 1930). Acco rdin g to the local inhabitan ts, frost does no t occurat th ese cleva tions in th e Sierra Mad re del Sur, a large rnountain

FIG. 43 . H uítzilac, Morelos, :-' Iexico . Hab itat of Sist rurus racu s. Snakesextromcly abundant in bu nchgrass mea dows bor dered by fir-pinc-ouk forest o( Photograph by ~1. Cran ger . )

70 SPECIAL PUBLICATlOl\;-~IUSEU~ 1 OF l\;ATURAL HISTOR Y

range th at is m ggecl and stcep, anel would seem to offe r Iittlesui ta b le h ábitat for grassland elwellers such as ra ttles nakes of th egenus Sistrurus.

The habits of Guerreran 5. raV ll S are comparable to those fromthe southern central platean. They are ale rt an cl q u íck to retreatwhen encou nte recl, but will stand their groll nel whcn escape is im­possible. Like most Sistrurus, they are more apt to turn and b iterather than eoil and strike . Stoo ls of some specimcns eo nta ine elroelent hair.

A female of th is species from th c vic inity of Hui tzi lac, :\ Io relos,gave b irth to seven you ng on 1 Junc 1974. Two other femalesfrom th e same localit y gave birth on 2~ M ay 1975 to nine an d th reeyou ng respectively. The range of va ria tion of the three broocls isas foll ows: total len gth 160-208 mm, mean 183 ; S-V 138 -19.2 mm,mean 166 ; w eight 3.9-7.4 g, mean 5.4. A cap tivc pair from l luitzil acwas observcd in copu lo on 1 M ay 1976 .

This rattl csnakc inhabits th e T cmperate Pine-Oak Forest as de­fined b y L eopold (1950).

DISCUSSIONThe foll owin g ob servations and cliscussion pr esen t OUT views on

various asp ccts of th e biology of M exican rat t lesnakes , and in dicatearc as where research is neeelecl conce rning th e ecology an d be­havior of th ese animals.

Habitat. Mo st mo ntane specics from Xlexico were clcscly asso­ciateel with rock y arcas ancl su ch mi crohabitats allowcd m áxim umprotection. Cr otalus l. lepidus, e. l. k lauberi, e. p . p ricei , and e. m.mol ossus were often locatcd in talus slopcs . Othcr mori ta ne rn tt lc ­snakes were founcl in pine-oak Iorcsts, mcsquite grassla nds an dhi ghlanel d eserts but usually rocky outcroppings w ere the dominantIea tu re . Crotalus irunscersus oc currecl in a rcas of vo lcanic rock,wher eas e. pricei niiquihuun us w as founel in situ ations wi th lime­stone bcdrock, Sorn e of the lowland taxa such as e. tluri ssus culm i­uatus inhab ited arid tropica l scrub for est with roc ky outcroppi ngs.Rattlesnakes wcre rarely [ound in cloud for ests .

\ Vhen first eliscovereel, smalle r montano taxa such as e. inlcr­m etlius, e. lepidus, e. pricei , e. pusi llus, e. trausocrsus, ancl e.ioi llard ! wo uld often rattl c and quickl y cruwl to safety within rocks .Many of th ese ra tt les nakc taxa sccmed to utiliz o specific retreats,for in so mc cases th e snakes craw led toward the collector in thei rendeavors to escape , when sui ta b lc retreats w ere available in th eopposite direction .

O UT fielel experience indicated that Mexica n ra tt lesnakes fro mh igher clcvations were most oftcn encou ntercd in microhabi ta tswith a so uthern exposu re (C . i. int c rm cdius, e. le p idus klau beri,e. l . morulus, e. m . molossu s, e. p. price i, e. transcersus} . A few

T HE NAT URAL HISTORY OF ~lEXICAN RATTLESNAKES 71

taxa tha t appeared to vary fro m th is mode were mo re frequentlyfound in rnicrohabitats with sou theastcrn (e . lepidus maculosu s,e. m. molossus, e. oiridis he lleri ), easte rn (e . pricei mi quiliuonus,e. w . u:illarili, e. te. silus], northe rn an d northeastern (e. iciltardime ridíonalis), an d western exposures (e. int ermedius gloy di ).

N carl v all rno ntane ra tt lcsua kes w ere found aboye a 1800 mcontour.. Lowland taxa which in vad e the M cxica n h ighla lJ(]s in­clude d e. du rissus, e. molossus, aud e. li asili scu s. Crotalus molos­sus and e. scutulatus inhabi tcd 10\Ver cleva tions in th c northcrnpart of th e range. A narrow ver tical d ist ributio n at rc lut ively lowelevation characterized the hab ítnt 01 e. steincgcri (a nd perhapse. lannoinii. Sist rurus racu s avo ided steep hillsi des, but was fo u ndon gentle slopes or in valle ys. It w as no t nec essari ly associatedwith rocky outcroppings, and was Iound also in lava beds. bunc hgrass bordercd b y fir Iorcsts, pin e-oak forests, and areas of grass,agave or cactus.

D egree 01 slope incl inat íon d clineated th e habitat of so rne ~ Iexi­

can rattlesnak es. Crotalus pri cei , C. pusillus, C. inte nurrlius, C.t ranscersus and e. lepulus oftcn iu hab it cd cx tre m ely stcep slo peswhereas C . ici ílardi w as Iound in inoun ta in vallcyx. uxuallv wi thpermuncnt water. Crotalus poltjst ict us and Sistrurus rllCtlS prcícrrcdrelu tively flat arcas.

Cround cover is ev idcnt ly a sig nifica n t cha racte ris t ic in thehabitat of sorne Mcxi can ra t tlcsnakc ta xa , aIHI vnri ed Irom ligh t(e . poly stictu s) to intermediate (e . pusi llus, e. trise riatus. S. racu s}.Crotalu s truusccrsus and C . t riset íatus (in som e urcux) in ha h ite dre la tivcl y open situ a t ions with a heuvv canopy.

D ai ly activity, Daily erne rgence al' \I exiean ra tt les na kes fromre trcats, particularlv montane ta xa , was ass oc ia te d wi t l: dillusedsunligh t and h igh atmospheric lnu u id ity. hnm ediatel v Followingthunderstorm act ivity, ruttl csu akcs h egan to e lne rgc an rl wcreoften e ncountcrr-d b ask ing 0 11 rock x which w erc st ill moi st. Ingene ra l, highland forms tended to he din rna I a nd th e lowlandtaxa , es pecia lly dnring summcr 1I1011ths, w erc nocturnal . T h e fol­10\Vin g M e xican ratt les nak e ta xa were Io und uhroad h~' d ay: e. b.basiiiscus, C. h . Oa,HJC IiS , e. cerastes . C. tlurissus tzalrcau , C. i. inicr­mcdius, C. i. gloUdi, C. t. omi lten ia nu», C. l. lc pidus, C. l. klauberi ,e. l. niaculosus, C. /. m oru lus, C. n út chc lli niuerícusis, C. 111. niotos­Sils, e. IJI. nigrcscc us, C. polust iclus, C. ¡J, pricc i, C. p. niiquíhuauus,e. pusillus, e. r. ru[;er, C. s. se/Jtu/atus. C. s. sa/villÍ, C . stcillcgeri,C. /ortligensi s, e. traIlS¡;CrSUS, e. l. /riserialus, e. t. (Ului/!JS. e.viridis !ld/crí, e. u;. lV il/ardi , e. le. a11w[;i1is, e. le. J/l cridiollalis,e. le. Si/liS, am] Sistrurus ra¡;lls. The fo Ilo\Ving \ Ie xiean rattl esnaketaxa w ere lOlllld as tl w ~ ' \\ 'e re pro",lillg b y ni ght : C . atro.\' . e.cerasles, e. d. dllrisslls, C. d. cu/milla /us, C. ti. tololla cus , C. c. eIl UO,C. e. jurr.;us, e. l. lep idu s, C . 1Il . lIl ilCflclli, C. lll . PUrrlllls, C. 111.

í2 SPECIAL PUBLICATION-~lUSEU11 OF NATURAL HISTORY

molossus, e. polij stictus, e. price i m iquihuanus, e. r. ruber, e. r.lu casen sis, e. s. sc utulatus, e. tigris, and C. triscriatus aquilus.

Adult snakes of three taxa (C. iute rtne d ius om iltc ma nus, e. l.lepidus, e. t. triscriatus} remained in the sanie location for a periodof ovc r two weeks and utilized the same ro ck for b asking dail y.Ju veniles of th ese tax a were cncountered prowling by night, per­haps to avoid predation while dispersing.

During the rainy season, pairs of e, in terniedius om lltc m anuswer e euco untc rcd in the field .

Seasonal Oeeurren ee. The onset of the rain y season in Mexícostim ula tes rattlesnake scasonal activity , For example, 55 speci­men s of Crota lus pohjst ictus from sou thweste rn Jali sco were ob­se rve d during a three day period in th e rain)' season, whereas onlythree snakes were secn during a comparab le period in May b eforethe beginll ing of th e rai ns. Seve ntce n specime ns of e. lepidusniorulus were Iouncl during ou e da)' after th e first major rain nearCaleana in the Sierra Madre Orienta l; on ly three iudividuals wereseen during June. Th e seasoual activity of most other Mexican rattle­sna ke taxa corr esponded to the patt ern no te d aboye. E xcept íonsincluded e, l. lepidus and e. l. kl au beri which we re found th rou gh­out th e year if th e tem perature was warm. These two ta xa haveacla p ted to a more arid environment,

Faunal and Climat ic Assemblage s. Kendeigh (1!).'54) an d Duell­man (196.5) revi ewed metho ds used in int erpreting Iaunal assem­blages and discus sed th e limitations inherent in th ese co ncepts. TheLife -Zo ne Concept of ~ Ierr iam (1890, 1894) was envísione d as ala titud inal transcontinen tal lielt or vertical zonation b elt in mo un­tain ou s arcas whích incorporated fa unal an d flora l info rmationwith add itional clima tic data, particularly temperature. The L ífe­Zon e Co ncep t was used by Go ldman (1951) and applied to th ezoogeog raph ic ch arac teris tics of Mcxico in order to evaluare thedis tri b ution of birds, mammals, and the flora community. Stuart(196--1 ) fc lt that Coldman's summary tended to reflect th e Bioti cProvince Concepto The Bioti c Province (Ves ta l 1914; Dice 1943,19.52) w as defined by D uellman (196.5) as ".. . a considerab le andcontinuous geographic arca th at is characterized by th e occurre nceof one 01' more important eco log ica l associa tions th at di fler, at leastin prop ortional ar ca covcred, fro m th e associations of ad jacentprovinces." Smith (1939), ut ilizing th e lizard gen us Scc lopotus, at­temptcd to map biotic provinces in Mexico. Later (1940, 1949) hemodified h ís position con cerning the ap plica tíon of th e b iot ic prov­inc e concept (see also Pet ers 19.5.5), Sm ith (1960) no te d , ".. . ex­tensive ag ree me nt of range limits of numero us species is a ncces­sary assllmption in acceptance of th e \'al idity of th e biotic provin ceconcep t." It is llnlikel y that an)' t\Vo plant 0 1' an imal species areaffec ted idenlica lly b y al! en\'Íro nmental compo nen ts; conseque ntly,

THE NATURAL HISTORY OF ~IEXleA01 RATTLES01AKES 73

no two sp cci es or subspecies can b e expec ted to have id entiealrange s.

13earing th ese diíficulties in mind, we attempted to delineateth e pattcr ns of di stribution of 42 taxa of Me xican rattl esnak es byco nsult ing tw o fa unal an d two clirnatic assemb lages: Life-ZoneConccpt of Goldman (1951). Biot ic Province Concept (Stuart 1964),T emperature and Ra infall Pr ov inces (Page 1930). an d th e Koeppenclimatic classi ficat íon sys tc m. The last sys te m, outline d b y Koeppen(1900, 1948), Koeppen and Geiger (1930-39) and summarized b yViv ó (1964), rou ghly d elineates the climatic types and ut iliz cs datafrom annual and monthly avc rages of tern pe ra tu re and precipita ­tion, inc1uding th e variab le c ílec t upon plant g row th throughevaporat ion.

Frequency of occurren ce for di strib ut ional overl ap is presentedin Tablc 1. Two ta xa (C. atrox, C. 1/I 01 0 SSllS nigresccns} occurredin six Koeppen provinccs. Crotalus atrox and C. d. tlurissus in­habited six and five biotic provinces, respectively . Four Life-ZoneProvinces were applicahle to C . t . triscr ía tus. Crotalu s 1/l 01 0 SS11 S

nigresccn s and C. s. scutulaius occurrcd in five ra infall provin ccs,and C. airox inhahited íivc tcmperatu rc provin ces.

The validity of physiographic, climatic or b ioti c pr ovin ces, atleast when uscd to exp la in th c d istrih ut ion of rattlesnak cs in lerrainas complex ph ysiographicall y as Mexico , is highl y tcnuou s, Thedis crcpancies Failed to p roduce an cxpla na tion of d ist ribu tion th atca n be co nside red to b e either va lid or useful. H ence, an analysisof th e cco log ica l requ iremc nts of rattlesnakes mus t be concerne dprimarily with th e m icrohabi tat or hab ita r nic ho (Dam mann 1961).

Food. Our field expericncc suggcs te d th at th e occurrence ofmontan e ra tt les na kcs in a gi vcn habitat was re lated to the avail­ability of mcmhers of th e lizarc1 genus Sceloporus. The den sity ofrattl esn ak e populations w as co nsiderahly g reate r w hen an areasu pportc d a large number of liza rds. especially species of Sccloporuswhich a re largc1y saxico lous . \ Ve sus pect that the Iccdi ng patte rn sof th e smalle r montan o rattlcsnakcs are corrc la ted wi th th e diu m al

T A B!.E 1. Freq ueucy of occ u rrcnc e for di st ri butional overla p in 42, taxa ofMexícan rat t lesnakes accordí ng to bioli c or climatic c1assification s. Per cc nta gefoll o\\' ed by mll llb e r of taxa ill pare ntheses.

Numb cr of Biotie or Climaüc Prot:irl ces 111,, 'h iell Ta xa Occur

Classiiicat íon Systelll 1 :2 3 4 5 6

T emperatu re ( Page 1930 ) 67(2,8 ) 24( 10) 5 ( 2, ) 0(0 ) 5( 2 ) 0(0 )Rainfall ( Page 1930 ) 50(2 1) Hl ( 8) 2,1(9 ) 5(2,) 5 (2,) 0(0 )Lif c-Zon c ( ( ;old man 1951) 74( 31 ) 19( 8) 5( 2,) 2, (1 ) 0(0 ) 0(0 )Bioti c Proviuce ( Stuart 196,' ) 5:2 ( 2,2, ) 19( 8 ) 2,1 (9 ) 2, (1 ) 2(1) 2(1 )e li mate ( Koeppe n ] 900, ] 948 ) 33(14 ) 33(14 ) ]4 ( 6) ] 2,(5 ) 0(0 ) 7(3 )

í 4 SPECIAL PUBLICATION-~IUSEU~ [ 01' l'\ATURAL HISTOR Y

activi ty patterns of va rio us species of Sce lopo rus . On one occasionin th e ea rly a fte rnoon a t Llano Crande. D ura ngo, a Sceloporuspoinsc tti clnr te d fr om a c lu rn p of ro cks an d d iecl a Iew minu tes later.Afte r five mi nu tes , un adult e. p. pricei em e rged , trai led th e lizarda n c1 cous uin ed it.

Captive e. pr icei , e. intcrmctlius, e. lcpidus, e. ir iseriatus, ande. ic íllardi showe d a mark ed prcf eren ce for liza rd s ra ther thanrodents. T he snakes us ua llv s truck the liza rds in th e th oracic re­g ion ancl h eld outo th em until mov ement ceased. \ Vhen roclen tswerc st ruck. thcy w e re, in most ca ses . re lcasccl, C aptive juvcni leex a mplcs of the la rg e r lowl and rattl csuakc taxa p ref erred a ppro­priat e size d lab oratory mice .

R itu al ized Mule Combato C rotalus atrox , e, intermedtus g loyd i,e. i. om iltc num us, e. lcpulus klaubcri , e. pusillu s, e. t. trisc riatus,e. t . aquilus, a nc] Sist rurus racu s engagccl in ritu uliz ecl maje COIll ­

bat in cap tiv ity . A dcta ilecl d cscription has bccn pub lishecl fo re. lc pulu« (Ca rpente r c t al. 1976) an d a com para t ive an al ysis ofth e other taxa \V iII b e Iorthcomi ng (rn a nuscrip t in prep. ).

Courtship aud M at ing Beh a vior. The Iollowing :\ Iexiean ra tt lc­su akcs w cre observccl engaging in cou rtsh ip a nd / or mating b e ­havior in captiv ity : C rot alus atrox , e, ca talinen sis, e. d urissus cul­niiuat us, e, d . tzab ca n, e, d urissus ssp .. e. e . C Il Y O, e. intc rm e d iusomiltcmanus, e. l. lepidu s. C. l. klaubcri, e. l . m orulus, e. 1/1.

muchclt ', e, 11l. mu crtcnsis, e. molossus nigrcscens, e. ]J. pricei,e. pu sillus, C. t . tr iscr ia íus, e. t. aq ui lus , e. IC. ici ilard t, e. w.arnabilis, e. ru, silus. nnc] Sisirurus m CllS.

The general pattcm of co u rts h ip and copula t ion is su mm a rizc din th e foIlo\Ving accou nt, Sh cd d ing b y th e Icm alc often stimu la te c1m a lo co u rts h ip ac t ivity and the Iemal e Irequcntly d cf ecatcd. pre­sumab ly to e vacua tc th e cloaca . Thc m ale cli rcctecl head-bobbinga mi tongue-Ilicking se quc nccs upon the h ead a nd dorsum of th eIema le. [f th e fem a le was in a resti ng coi l, th e m ale m ight vigor­ous ly p ress hi s 10\Ver jaw agains t her bod y in o rd er to stim u la tehe r to c ra w l. T h is action a llowcd fo r a lig nme nt of th e bodi cs. T heh eacl-neck a ng le of th e maj e varicd b et w ee n 30-4.5° a nd th e male'sme nta l rcg iou was pressecl on th e Iem nle 's do rsum, T he dorsa l acl­va nee movements b y th e male , either sagi t ta lly, para-sagi t ta lly orlaterall y, iuclu rlecl a h ead-bobhing Illoti on \Vhich va riec1 iute rspc­eifiea lly fro m 110 lateral mo\'emellt to a pronouneec1 sicle-to-sic1emo tioll . Female e. al rox as su llle d a rai sed head a nd a nte rior tru nkstanee 011 oceasion: possibly thi s \\"as a reject ion posh lJ"e (m a nus erip tin prep .). As the m ale di reete cl courtship act ivitie s to\\"a rd th e fe­m aIe. sIl(' ra ised her tail a ncl ga ¡w d tb e cloaca (as in e. alrox , e, rl.tlurissllS, e. ¡JllsilhIS) \\"hich of teu stim u la te d the ma le . The male e n­eireIecI tb e female's tail \Vith bis ta il a1HI rapid ly slid hi s cauda l con­figuration iJl an teriorly am i post eri or!y c1irected movem cn ts (as in e.

THE NATU RAL HISTORY OF ~IEXICAl\' H.ATTLES~AKES 75

ilurissus tzubcan , C. C!. durissus, C . c. CIl YO, C. pusillus]. This be­hnvior has been termecl th e "s t rokc-cycle" (Chiszar c t al . 1976).The male draped lar gc-radius coi ls ove r th e Iem alc's bocly an d at­temptecl to place the clo ucae in apposit ion b y slídiug h is ta il u nderthe tai! of the fem ale. The malc might pu sh b ackw ards agai ns tthe resistance of th e Icmale's tai l as he inscrted (as in C. d . d urissus,C . pusillus). Only on e hem ip enis was inserte cl, anel eversión ofth e hernipen is prior to ins ertion was ne vcr obs erved. T he tact ile­chase anel tactile -ali gmncnt pa t terns va ried fro m 4 m inutes inC . ioillarili to over 3 hours in C . p usi llus. The range of var ia t ionmi ght be clue to fe male recept ivit y. Co itus va ried from :2 hoursin C . airox to 9 hours in C . w . ic illonl í. j erking aud twitching gen­erallv cea secl when intromission occurred, but often the malemai¡;tained a steady pulsat ion of th e bocly near the tail (as in C.atrox, C. pusillus). T hc Fcmalc mi ght drag th e ma le backwardsby th e attach ed hem ip enis (observe d in C. atrox, C . d . d urissusíuntil separution occu rrcd .

Rcproduction. The rainy se ason in Xlcxico usual lv occu rs be­tween May and October, aud th e dry se ason betwecn Dccemb crand April. In parts of so u theru Xlcx ico, a short dry season occ u rsduring the su mmer raiu y period o Du ring lat e [ u ne ami carlv [uly,th e raiuy se ason no rm all y bcg ius in northern Xlcxico. 111 lat e Julyand Septcmbcr, th e ra iu y scason starts in cen tra l and sou thernMcxico. The northwest arca of Baja C aliforn ia rece ives w iu terrains whereas th e sou thern scction rcccives sum rncr rains.

In compiling literaturc refe rences and ou r observations onparturition in wi lrl Xlexican ratt lcsuakcs. w c acc um ula ted th e fol ­lowing elata on broods: 11 lit ters w ere bo rn in [un«, 1:2 iu July.16 in Au gu st , :2 in September , 1 in Octob cr , aud 1 in [ anuary .Compiled obscrvatious on our capt ive individuals rcvcalcd 5 litte rsboru in [une, 4 in [uly, S in Allgn st , .! in Septem b er, and 1 inOctober. Data on these ra tt lcsnake taxa are listecl in Tab le 2..Parturition in .\ rexican rattl csnakcs stud ied to d ate coincides wi thth e rainy se aso n , possihly due to a g rea te r abundancc of potcntialIood it eins ava ílab le at th is time.

'Varnillg Mcchanism s ami D efeu sive Act ions. I n addition toth e use of tit e ra tt le as a warniug mechan ism anel th e striking co il,a number of othe r cle fcnsivc hchaviors were observc d by us inXlcxican rattlcsnak cs. \ Vhcn scized b y colle ctillg tongs, munv ofth e smaller montano taxa turned and bit in lieu of assull1in g astriking coil. Some , es pec ia ll>' C. ill/Cfl Il Cdi ll S, hegan sp inn ing ona longitudinal axis. Adult C . dllris,\'llS /;:..a!Jcall rais cd th c antc riorportion of th e body in an aIlllo st \'cr tical COlUlllll with a lateralbenel in th e ncck, al1(l faccd th e intruder. Captive jU\'ellil e C . d.t ;:a{¡ ca/l flattcncd and ro tated th eir head anel cerdcal reg ion asmuch as 90° so that th e do rsal asp ect, with the co ntras ting pattern

76 SPECIAL PUBLICATIO:\'-~ruSEU ~ t OF NATURA L HISTORY

on the hcad and the dark paravcrtebral neck st ripes, was visible.Young cap t ívc G. tlurissus totonacu s in fl ated th eir trunk , exhí b ite dconvu lsive movements and, on rare occasions, Hipp cd ove r uponth e dorsum wh en eonfrontcd by a h uman obs crver. Crotalus poly­st ictus usu all y thrash ed wildly wi th pronounccd lateral undulati on sw hc n handlcd , this snake some timos retumcd to a striking coilwhen cornered, An ad ult G. s . sc utulat us ancl sorne exa mples ofSistruru s ravlls rcpcatcd ly Ila ttenccl the ir heads and trunks on th esubstrate , th en lift cd the tail s ve rt ically and wav ed th em slowlyin response to the p resence of h uman s. The snakes did not attemptto rattle . Sorn e of th e smallc r ra t tlcsna kes responded to th e pres­euce of live mice and rats by launching in to a st riking co il, th enst ruc k th e rod ents with closc d mo uth. Hattlesnakes react ed tokin gsn ak cs ancl o thcr ophiophagous snak cs by forming pronouncedbody-u ridges which wcre us cd to strike the preda tors . D ermalsubstances of ophiophagus snakes eli ci ted b ocly-brid gin g responsesFrom a number of Mexican rat tlesnake taxa (Weldon an d Burgharclt,1979 ). C rotalus toriugcnsis, when touched , used vertical body­bridges 01' lateral Ilexures to strike an annoying object, Frequen tly,th e [orce \Vas grea t enough to knock Ireshly killed ro cle nts fro mth e Ieeding Iorceps.

Crotalu s ste incgeri verti cally elcvutcd its tail and a portien ofth e pos terior trunk ancl he ld th cin rigid ly as it ass umcd a strikingcoil. Althou gh Klauber (19.56) \Vas un aware of an open mo uth

T.~nLE 2. Dal a on rat tlesnake lítters wi th viable you ng showing number ofyoung, length of young, an d weight of young. Numbers in paren theses arernea ns.

X lI lII t¡e r T otal lcngtli WeightTax on oi uo ung (//l //l ) (g)

C. atrox 6--25( 14.3)C. durissus ssp . 10C. d. tzahcan 21 290-350( 316) 18.4-26.8(23.4)C. e. [u r cu s 7 206--222(213)C. int crmcd ius omi ltcm auus 5 19-1-212(205) 4.9- 5.4 ( 5.2)C. l. Lcnidus 6 165-190(177) 5.0- 5.7( 5.2)C. l. klau hcr! 3--- 5(4) 181-196(191) 6.3--- 7.0( 6.6)C. l. niorulu s 4C. //l. mitclt r[l i 1 275 17.5C. //l . m ucrt cnsis 4 143---179( 167) 3.3--- 7.0( 4.9)C. 711010 .1.\ 11.1 nigrcscens 5 291-316( 304) 25 .-1-27.4(26.6)C. l' aly~1 ict l/ S 5-12(S) 155-287(214) 2.4- 1I. 5( 8.9)C. 1'. ¡nieei 3--- 9 (5 .3) 152-1S5( 16-1) 2.7- 5.6( 4.1)C. 1'. núq u íh utuvus 4- 5( ·1.5) 130-143( 135) 2.6( 2.6 )C. nusillus 3- 5( 4) 165-179 ( 171 ) 8.0- 6.1( 4.0)C. l. triscriat l/ S 4- 6 (5) 159-178( 168 ) ,1.8- 5.1( 4.9)C. t. aq u ílus 2- 7(4.7) 120-192( 16S) 4.9- 8.S( 6.1)C. ici llardi .\ i/ I/ S 4- 5(4 .,'5 ) 146--21S( 190) 4.9- 6.9( 6.0)Si.llrur ll s rac us 3--- 9( 6.3 ) 160-20S(1 83) 3.9- 7.4 ( 5.4)

TIlE NATURAL IlISTOH.Y 01" MEXICAN RATT LESNAKES 77

threat en in g postu re in ra ttlesnakcs, th ree C. molossus nigrescensobse rved by us rep eat cd ly cxh íbite d this beh avior for pcríods aslon g as Iivc minu tes. On e C. polusti cius also assurn ed thi s po sture.

Crotalus atrox, C. lepidus, C. molossus, C. scutulatus, and Sis­trurus racus emitte d mu sk upon ca p tu re . An adult C. duri ssus di s­chargcd a stream al' mu sk wh ilc bcing res traincd.

RESUMEN

Se presenta información sob re la cco log ía e historia natural de4.'5 taxa de cascabeles mejicanos, ge ne ros Crotalus y Sistrurus.

Observacio nes de la fisiografía, ge olog ía, clima, y la vegetaciónde .',Iéxico son regi stradas en lo qu e se refier e a los cascabeles deesa región . D a tos ele obs er vaciones tomad as direct as de poblacion esna turales y ejemplares capt ívos son list ad os, incluyendo los pr edilec­ciones de h abitación, extc ncion cs de area y elevación, rc produc ión,periodos de actividad, y com portamiento.

La mayoría de los cascabeles monteses habitan bo sques depino y encino, llanos cubierto de hi erba, y des iertos de altur a.Generalm ente los afloramientos rocosos son un factor deter minante.Algunas taxa de tierra baja se enc ue ntran en b osqu es tropical esáridos con afloramientos rocosos. Refugios específicos son a menudoutil izad os por cascabeles monteses. ¡\ Iicroh ab it aciones con or ien­ta ción hacia el sur son habitadas con mas Ircqucncia por cascabel esde los altos , scquido por el sudeste , es te. no rte, norest e, y oes teen el orden de prefer en cia. Casi todas las taxa mo nteses seencuentran a 1800 metros o m ás de a ltu ra, Una dis tr ib uc iónlimitad a en elevaciones relat ivmu ente bajas caracterizan la h abi ­tación dc Crota lus st cjnc ger¡ (y ta lvez C. lannomií; Sistrurus Ta CU S

es un a excepción ya qu e es te se encue ntre en asociaciones variadas.E l grado de inclinación de la fal da es im portan te. La den sid ad dela vegetación va de leve a mod erado.

Hayos del sol difusos y alta humid ad atmosfér ico con trib uy ena la ac tivi dad diaria, especialmen te en la s cu lebras qu e habitanregiones monta ñosas. Especies de tierras alt as tiend en a ser diurnasy las de tierras bajas nocturn as, especialme nte en el ve rano. Treintados taxa fueron encon trados activas durante el día y diez y och ofueron cazadas de noch e. Serpien tes adu ltos (C . intcrin edius, C.lcpi tlus, C. triseriatus} pueden permanecer en el mismo lu gar porlo me nos dos semanas y ut ilizar la misma pe ña par a tomar el sol.Ejemplares juveniles de es tas ta xa fueron encontradas de noch e.

La actividad de cascabe les en M éxico dep ende de la epocallu viosa. Pocas cul ebras se enc ue ntran durant e la epoca seca.

Los pat rones de di st ribución de cas cabeles mejicanos no seexplican por uso de asambleas faunales ni climáti cas. La frecu enciade traslape di stribucional involuc ra be n tanto como seis provincias

78 SPECIAL PUBLICATIO N-MUSEUM OF NATURAL HISTORY

fau nales O climáticos para una forma de cascabel. Estas discrepen­cias sug ieren q ue los requisitos ecol ógicos de los cascabeles ti en enquc ser primariamente evalua do s co n un análisi s dc microhabitacióno nich o habitacional.

La ocurren cia de las culeb ras montanescs se relaciona, enparte, a la di sponabilidad de especies dc Sceloporus. Muchas delas culeb ras peque ñas de altura mu estran una decidida preferenciapor la gartijas como comida y la s cascabeles jóvenes de tierra bajaprefieren ro edores pequeños.

Combate ritua lizado cutre machos fu c obs ervado cn G. atrox ,G. intermedius gloljd i, G. i, om ilte manus, G. lepidus klauberi, G.pu sillus, G. t. triseriatus, G. t. aquilus y Sisirurus ravlls.

Los asp ectos de cortejo y/ o brama fueron registrados endi ecinu eve di st int as cascabeles ca ptivos, Un patrón ge ne ralizadode compo rta miento fuc apare nte y es ta descrito.

Parturación en los cascabeles mejicanos estudiados hasta lafecha coincide con la epoca llu viosa . Informaci ón reproductiva d e19 ta xa es present ada.

Compo rta miento de adverten cia, adicional al curollamiento,a taque, y resonamieuto, inclu ye lo siguiente : torneando y mor­di endo, rotando en su axis lon gitudinal , rotación dc la cabeza ycuello, elevac ión vertical dcl cue rpo anterior, inflación del cue rpo,movimientos convulsos, aplas ta miento en el suc Io y undulaciónlente dc la cola, lanzando co n boca ce rrada, am enanza con bocaabier ta, ele vac i ón ve rtical r ígida de la cola y emision de almizcl e.

APPENDIX

Range o r altitu de extcnsious for Mexican ra tt lcsnakc taxa reportedin texto

Crotalus b , basili scus

Crotalu s bnsiliscu s oaxac us

Crota lus d urissus culm inatus

Crota lus durissus totonacus

Crotalus i. int crniedius

Cro talus intermedi us gloljd i

l\lICHOACÁN: near DosAguas in th e Sierra deCoalcomá n (2225 m)

OAXACA: 35.5 km N\VTelixtlahuac a

~lICIIOACÁN : 7 km \VMorelia

TA~lAULIPAS: 20.8-48 km NSoto la Marina

PUEBLA: near Cacaloapan

OAXACA: near Cerro Machín(Sierra de Juárcz), Suchixtepec(Sierra de Míahuatlán)

T HE NATURAL HISTOHY OF r-.IEXICAN HATTLESNAKES 79

Crotalus int ermedius om iltemauus GUERRERO : 1.6 km S\V Filode Caballo, San Vicente, 1 kmN Puerto del Gallo

Crotalus lepidus morulus ;\,UE VO LEóN: 24-32 km N\VGalcana

Crotalus steinegeri SINALOA: Ejido Tebaira

Crotalus triscriatus aquilus HIDALGO: El Chico (3110 m)

Sistrurus ravus GU ERRERO: mountains ofCentral Guerr ero

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THE l\'A TU RAL HISTORY OF ~IEXICAl\' RATTLESNAKES 81

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THE NATURAL HlSTORY 01" ~IEXlCAN RATTLESNAKES 85

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INDEX TO HERPETOLOGICAL SCIE NTI FIC NAMES

PACEAgki stro do n p isci corus _ _ __ 37Ano lis . __.. . .__ __ 56Botlirops barbo uri .__ __ __ .__ .____________ __ . . . 22Both rops un d ulatu s . .__ .__..__ __ __ ._ .. __ .. . 22Cu cmidop horu s .__ . . __ .. .__ . .__ . .... __ ..... 10, 56Crota lu s __ . .. .. __.. ........ __ __ .__ __ . o 6,12, 56 , 77

atrox o • 4 , 71 , 73, 7·1 , 75 , 76 , 77 , 78basiliscus __ ._.__ . __ .. ..__ . . 4, 6, 3 1, 71luts liisc u» hasil iscu s o • • .____ • 6, 7, 8, 43, 71 , 78ha siliscus oaxacus __.. . __ . .. ________ __ __ __ __ __ .. __ 6, 8, 71 , 78catalinr nsis .__ . __ . .__ ........ __ .. 8, 74cerastes ... __... ._ .... ......__ ......_.. .__ . . . _.... ... 9, 10, 49, 7 1ce rastes ccrcobombus . __ o • __ .. • .. 9, 10ce rastes latcrorcpcns .. __ .. . 9du rissns . 10, 12, 13, 14, 15, 71 , 7:>, 7·j, 75 , 7(j, 77durissu s cu lnünatus _ __ o 7, 11, 12, I -l, ·13, 70, 71 , 74, 78d uri ssus cU1lla ncns is .. __ .. 11tlu rissus d uriss us __ __ 10, 11, 14, 71, 73, 7·1 , 75durissus tot olla cu s 10, 12, 13, 1·1, 71 , 7B, 78d uris su s tzab can .. __ __ .__ 14, 15, 16, 71 , 74 , 75 , 76cnyo . ._ .__ __ _.. __.. __ . 16c rujo Cll Y O __ lG, 17, 30, 71 , 7·1 , 75cnyo [u rcus __ ..__ .. __ . 17, 18, 63, 71 , 76intcrm cdiu s .. __ __ .. __ 18 , 70, 71, 74, , J , 77int er mrdius glo yd i __. . . __ .... __ . 8, 19, 20, 21, 71, 74, 78int ermctlíus intcrmed ius __ 18, 19, 70 , 71 , 78in tcrm cdiu s omi ltcmanus ... . 20, 22, 23, 71 , 72, 74, 75 , 76 , 78, 79lauuom i .. .. __ __. ...._. . . __ . ... __ .. 71 , 77lcpidu s . 22, 26, 29, 33, 39, 43, 59 , 61, 63, 64, 70, 71 , 74 , II

THE NATURAL HISTORY OF 11EXICAN RATT LES NAKES 87

69, 70 , 7777, 78, 79

3 170, 72, 74, 76,

61, 6:2, 63,10, 39, 63, 64, 65, 66, 67, 70, 71, 74,

______________ ___________ ______ 64, 65, 7 1,26, 39, 64, 6.'5,

17, Ci 6, 67, 68, 71, 74,63, 64, 65, 66, 71, 74,

PACElepidu« klauberi 22, 24, 25, 26, 32, 61, 70, 71, 72 , 7·1, 75, 76, 78lcpidus lcpidu« 22, 24, 25, 26, 70, 7 ] , 72, 74 , 75 , 76lcpidus maculosu s 7, 22, 25, 26, 27, 71Icpidus motulus 22, 2-1, 25, 26, 27, 28, 29, 70, 71, 72, 74, 76, 79m üclielli 29, 3 1mit chclli lIlitchclli _____ 17, 29, 30, 71, 74, 76mit cliclli tnu crtcn sis 31, 71, 74 , 76mu clicll í )lyrrllllS 10, 30, 31, 62, 63, 71molossus 6, 8, 3 1, 32, 39, 48, 7 ], 77molossu s cstc bun ensis 32molossu s lII ol osSIIS 32, 33, 70, 71, 72niolossu s nigresccu s 6, 26, 27, .'32, 3.'3 , .'3·1, 69, 71, 73, 74, 76, 77nolustictus 10, 34, 35, 36, 37, 71, 72 , 76, 77pricei 33, 38, 41, 63, 64, 70, 7 1, 74pricei )lricei 26, 27, 38, 39, 40, 42, 64, 70, 71, 74, 76pricei uiiquihuan us _ 40, 4 1, 42, 43, 70 , 7 1, 72, 76pu sillus 7, 43, 44, 45, 46, 70 , 71, 74, 75, 76 , 78rubcr ·16, 47, 61rubcr lorenzoen sis 47ruber lu cascn sis __ _ 8, 16, 30, 47, -18, 71, 72ruber ruber ___ 47, 48, 62, 63, 71, 72scut ula tus _ _ 4, ,18, 71, 77scutulatus salcini __ 49, 50, 51, 71sc ut ulatus scu tula tus __ 48. 49, 50, 7L 72, 73, 76st cjncgeri 7, 50, 52, 71, 76, 77 , 79ti gris ]6 , 50, 52, 53, 7 1, 72tortu gen sis 53, 7 1, 76tran sc ersu s 53, 5 1, 55, 56, 70, 71triscriatus _ 1, 22, 5Ci , 71, 74, 77tr iscriutus aq uilus 56, 58, 59, 60, 61, 71, 72 , 74, 7Ci, 78, 79tri scriatus tr iscriat us 43, 53 , 55 , 56, 57, 58, 59, 61, 69

71, 72, 73, 7·1, 76, 78__ ___ _______________________ 61, 62

617175747176751010

__ 565637375656

____ 22, 26, 42, 56, 72, 73, 7·1 , 7856

_ 6339, 74

63

ciridtsoiridis caliu iuusc irulis h cllcritcillardi _icillard¡ anuthilisicillurdi m cri di onalis _ _ _willardi s ilusuiillardi icillardi _

Crotapluttu sDi)lsoSallTll s _

C crthon otus _llyla _Lanniron clt is t t iaugulu ui arciicraLiclianu ra t rici rgaia roscojusca _N crodiaPlnjilodacujlu »Sc cloporu s

l1Cn ClI S _

jarro d _poinsc tt i _ _undulat us _ _

SistTIl rus _ _t üc ü« _ _ 51 , 57, 68, 69,

Strcplosaurns III Cl1T11 si _ _ _

88 SPECIAL PUBLICATION-~lUSEUM OF NATURAL HISTORY

PACETliamnophis _ . .__.. .__..._.. ._. ... 56Uma _ 10Uta __ ---- 10, 56

stan sburiaua .__ 31Xantu sia .... ..._. ...__. . ._. .._._..__. . ._... . . 56

States of Mexico

1. Aguasca lien tes ]í. Morelos2. Baja California del No rte ]8 . l\'ayar it3. Baja Ca lifornia del Sur io. Xu cvo Leon4. Campeche 20. Oaxaca5. Chiap as 21. Pueb la6. Ch ihu ahua 22. Qu eretaroí . Coahuila 23. Quintana Roo8. Co lima 2-1. San Lui s Potosi9. Di st rito Federal r¡ - Sinaloa_ ;J .

10. Durango 26. Sonora]1. C ua najua to r¡- Tabascoz t ,

12. Guc rrcro 28. Tarnaul ípas]3. Hidalgo 29. T laxcal a14. Jali sco 30. Ver acru z]5. l\l exico 31. Yucata n]6. Míchoacan 32. Zacatecas