Cave-dwelling Batsof Nort h e rn Mexico

Merlin D. Tuttleand

Arnulfo Moreno

© Copyright 2005 by Bat Conservation International, Inc.ISBN # 0-9742379-5-7

All rights reservedPrinted in Mexico

Requests for permission to reproduce material from this work should be sent to:Bat Conservation International, P.O. Box 162603, Austin, Texas 78716.

Their value and conservation needs

Ack n owl e d ge m e n t s

This book would not have been possible without the enthusiastic encouragement and

financial assistance of Eugenio Clariond Reyes, Chairman of the Board and Chief

Executive Officer of Grupo IMSA. The U.S. Fish and Wildlife Service Intern a t i o n a l

P rogram provided additional funding for this publication, and the Disney Wi l d l i f e

C o n s e rvation Fund and Bat Conservation International supported essential field re s e a rc h .

The authors also gratefully acknowledge the invaluable collaboration and/or financial

assistance of Fondo Mexicano, PRONATURA, the Instituto Tecnologico de Ciudad

Victoria and the Museo de Historia Natural de Tamaulipas. Their collaboration contin-

ues to play an essential role in our efforts to conserve the bats of northern Mexico. We

also thank Travis and Bettina Mathis for their continued support of this project.

Robert Locke edited and designed the publication. Dave Waldien provided extensive

review and project oversight. A. Nelly Correa Sandoval of the Instituto Tecnológico y

de Estudios Superiores de Monterrey provided logistical support, and XXXXXXXX

translated the original manuscript from English to Spanish.

Fondo Mexicanopara la Conservación de la Naturaleza

C o n te n t s

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Bats as Essential Allies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Why Bats are Feared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Threats to Bat Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Investing in Bat Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Where Bats Live . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Lives of Cave-dwelling Bats

Selecting Homes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Finding a Mate and Rearing Young . . . . . . . . . . . . . . . . . . . . . . .24

Navigating in the Dark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Traveling Long Distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Finding Food

Special Adaptations for Hunting . . . . . . . . . . . . . . . . . . . . . .28

Co-evolving with Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Understanding the Diverse Faces of Cave-dwelling Bats . . . . . . . . . .32

Bat Caves as Sustainable Resources

Guano Extraction for Fertilizer . . . . . . . . . . . . . . . . . . . . . . . . . .37

Wildlife Tourism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Appendices

Appendix I: Controlling Vampire Bats . . . . . . . . . . . . . . . . . . . . .40

Appendix II: Recognizing Former Bat Roosts in Caves . . . . . . . .44

Appendix III: Guidelines for Conserving Cave-dwelling Bats . . .46

Appendix IV: Precautions for Sustainable Guano Harvesting . . .47

Suggested Reading and Resources . . . . . . . . . . . . . . . . . . . . . . . . . . .48

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Cave-dwelling Bats

Some 4 million Mexican free-tailed bats emerge from aBorderlands cave to spend the night hunting insects.

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of Northern Mexico

I n t ro d u c t i o n

Bats have lived in North America since the age of dinosaurs,

and Mexico is home to 137 species, among the world’s most

diverse assemblages of bats. Caves of northern Mexico and the

southwestern United States shelter the world’s largest popula-

tions of bats. Single colonies number up to 20 million and con-

stitute the largest communities of mammals on Earth. Several

species have continuously occupied caves of northern Mexico

for thousands of years. Over such long periods, they have come

to play key roles in maintaining the balance of nature and the

health of human economies.

Our goal with this publication is to introduce the many val-

ues of bats and their conservation needs. We emphasize species

that form the largest, most conspicuous populations in caves

only because they are typically the most vulnerable and most in

need of help. The combined impact of bats that live alone or in

smaller, widely dispersed groups, however, is also substantial

and should not be ignored.

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Cave-dwelling Bats

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of Northern Mexico

Bats as Essential Allies

Bats are primary predators of bee-tles, moths, leafhoppers andother insects that are extre m e l y

costly to farmers and foresters – andthey also catch mosquitoes in ourb a c k y a rds. Just one Mexican fre e -tailed bat (Tadarida brasiliensis) can eatenough corn earw o rm moths in a sin-gle night to prevent 20,000 eggs fro mbeing laid. And that means a farm e rcan avoid spraying several acres ofc rops with costly pesticides. Imaginethe value of a bat colony that cancatch tons of insects nightly!

The 20 million Mexican fre e - t a i l e dbats from Bracken Cave in Texas con-sume about 200 tons of insects on anaverage summer night, including bil-lions of corn earw o rm and arm y w o rmmoths that cost U.S. farmers a billiondollars a year.

Because bats have been traditional-ly unpopular, they rank among ourp l a n e t ’s least-studied mammals.Recent re s e a rch, however, clearlydocuments their immense contribu-tions to agriculture in nort h e rnMexico and the southwestern UnitedStates. Scientists are still calculatingthe total economic value of Mexicanf ree-tailed bats, but it is already appar-ent that the continued loss of thesebats could seriously jeopardize cro p sand increase demands for pesticidesthat threaten human health and safety.

A large colony of free-tailed batscan help protect crops 80 kilometersor more away. In Georgia, a pecang rower who attracted thousands off ree-tailed bats to bat houses in hiso rc h a rds,now produces crops withoutpesticides in an area where other

8

Cave-dwelling Bats

Researchers (left to right) Jason Lee, John Westbrook and Gary McCracken prepare to launcha balloon that carries a bat detector and other instruments high into the night sky.The proj-ect showed that Mexican free-tailed bats fly as high as 3,000 meters to track down damaginginsects that migrate at that altitude.

g rowers spray six times per season.Many insects listen for the

“echolocation” sounds that bats emitto hunt and navigate, then flee are a sw h e re bats are detected. Scientists inthe United States are testing devicesthat produce bat-like hunting soundsto scare pests away from cro p s .

Other types of bats pollinate flow-ers and disperse seeds that sustainwhole ecosystems. More than 60species of agave plants, includingthose from which tequila is made, re l yon these bats as primary pollinators.Long-nosed bats are also import a n tseed dispersers for giant cacti. Theo rgan pipe cactus, which produces thelucrative pitayo fruit, relies on thesebats for both pollination and seed dis-p e r s a l .

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of Northern Mexico

So many bats emerge from Texas caves thatthey often dominate weather radar images.Thesmaller image shows the Doppler radar onesummer day at 6:15 p.m., as the bats were justbeginning to leave their caves (on the left) to movetoward the insect pests clustered over croplands (onthe right).Twelve minutes later they had spread thickly overmuch of Central Texas, eating insects by the ton.

The corn earworm moth (Helicoverpa zea), afavorite food of Mexican free-tailed bats, isone of the most damaging agricultural pestsin the Americas.

The droppings of cave-dwellingbats provide some of the world’s finestnatural fertilizer. They also supplynutrients required by whole ecosys-tems of unique organisms that liveonly in caves. Bacteria from these sys-tems have been used by major com-panies to improve detergents andother products of great value tohumans.

The loss of large colonies of cave-dwelling bats can threaten the eco-logical or economic health of whole

regions in both Mexico and theUnited States.

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Cave-dwelling Bats

The lesser long-nosed bat plays a criticalrole in the desert ecosystem by pollinatingand reseeding the cacti and agave on whichit feeds.This bat, taking nectar from theflower of an organ pipe cactus, carriespollen from plant to plant.The long-nosedbat on the opposite page will disperse seedsfrom the organ pipe fruit that it is eating.

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of Northern Mexico

Bats help keep the Sonoran Desert healthy. Long-nosed bats, which feed on the nectar ofcacti and agaves, are the primary pollinators for many of these plants.

Since bats are active only at nightand are usually difficult toobserve, they are often misun-

derstood. And it is only natural to fearmost what we understand least. In thePacific Islands, where giant flyingfoxes have wingspans of up to twometers but live out in the open likebirds, people appreciate them just asthey enjoy other wildlife.

In Mexico, bats certainly havenothing to do with Chupacabramyths, and the vast majority do notbite other animals. For every vampirebat, there are literally millions ofbeneficial bats. But because helpfulspecies live in much larger coloniesand are far easier to see, millions at atime have been mistakenly killed. -

Thousands of bat caves have beenb u rned, dynamited or otherw i s ed e s t royed, in the erroneous beliefthat this would eliminate vampires,although vampires can survive justfine without caves.

There are only three species ofvampire bats in the world, and theylive exclusively in tropical America,including Mexico. Only one, thecommon vampire (Desmodus rotundus),has been known to bite humans orlivestock. And even this bat seldombites humans, though it can harm cat-tle. Fortunately, it is easy to identifyfrom all other bats and can be con-t rolled without harming otherspecies. (See Appendix I)

Bats in general rank among the

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Cave-dwelling Bats

Why Bats are Feared

Commonvampire

bat

world’s most gentle animals. Like allmammals, an occasional individualcan contract rabies, but even thoser a rely become aggressive or bitehumans except in self-defense if han-dled. If bitten, have the animal testedfor rabies and seek medical evaluationand possible vaccination as soon aspossible.

Like bird droppings, bat guanocan contain a potentially infectiousfungus (Histoplasma capsulatum). Forhumans who do not enter caves, thereis little to fear. Those who explorecaves or extract guano should mini-mize inhalation of dust in the cave. Alung infection, known as histoplas-mosis, is typically no worse than flu,

but can be serious for those who care-lessly inhale excessive amounts ofspore-laden dust.

Despite decades of bat researchand being surrounded often by mil-lions of bats in caves, the authorshave never been attacked or contract-ed a disease from bats – nor have weever heard of a bat becoming entan-gled in anyone’s hair.

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of Northern Mexico

The common vampire is one of threespecies of vampire bat and the only oneknown to bite humans and livestock.

Bats are especially vulnerable todecline because they re p ro d u c em o re slowly than any other

mammal for their size and because asingle cave can be critical to the sur-vival of a large pro p o rtion of an entirespecies. In the state of Sonora, justone cave shelters more than 90 per-cent of the known breeding popula-tion of the endangered lesser long-nosed bat (Leptonycteris curasoae). Pro-tection of such key re s o u rces is vital.

Bats that form huge, conspicuouscolonies in caves are extremely vul-nerable to human disturbance andpersecution. Many caves that oncehoused great numbers, even millions,of bats, no longer contain any. In1990, a Bat Conservation Intern a-tional survey of the 10 largest batcaves known in nort h e rn Mexicofound that half had already lost 95 to100 percent of their bats. The singlemost important cause of decline was

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Cave-dwelling Bats

Threats to Bat Survival

Many cave-dwelling bats form huge colonies that number in the millions, like the Mexicanfree-tails that almost completely cover the ceiling and walls of this cave. In nursery areas, thepups are jammed tightly together in nursery areas.

intentional burning or dynamiting.C a reless human disturbance of bat

roosts in caves can seriously reduce am o t h e r’s ability to rear her young insummer or cause bats to waste limitedfat re s e rves in winter.

Sometimes entrances are closedout of fear of vampire bats or newshafts are dug for guano mining, forc-ing bats to abandon their cave becauseof altered air flows and roost tempera-t u res. Campfires in cave entrances cans u ffocate bats when smoke enterstheir roost or, even worse, they cans t a rt a guano fire that can burn form o n t h s .

O c c a s i o n a l l y, something as simpleas partial blockage of a cave entranceby trees or shrubs can intolerablyi n c rease the risk of bats being injure dor caught by predators, which canalso drive them from their roost.

F ree-tailed bats have suff e red seri-ously from pesticides used on cro p s ,

especially from organochlorines suchas DDT. Organochlorine, org a n o-phosphate and carbamate insecticidespose serious threats to bats, and syn-thetic pyre t h roids may, as well.

Long-nosed bats, meanwhile, aret h reatened with starvation becausethey depend on the nectar of agaveflowers, and agaves are being depletedr a p i d l y. The continuing loss of foodand shelter puts Mexico’s long-nosedbats (Leptonycteris curasoae a n d L. nivalis)at increasing risk.

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of Northern Mexico

Caves shelter untold millions of bats, but such bats are at high risk from human disturbanceand even intentional destruction, especially when their caves are conspicuous to people.

Cave-dwelling bats form con-spicuous, slowly re p ro d u c i n gcolonies in relatively few caves

w h e re they are exceptionally vulnera-ble to humans who misunderstand,fear and persecute them. They are, asa result, among our most rapidly

declining and endangered wildlife.Their survival – and our own wellbeing – depend on our ability to over-come unfounded fears and to re s p e c tand protect them as allies. Success canbe an invaluable investment in humanhealth and secur i t y.

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Cave-dwelling Bats

Bats provide many beneficial services to the environment and to humans.Among otherthings, they help control many troublesome, often expensive, pests. Pallid bats even dine onscorpions.

Investing in Bat Conservation

Conserving bats on large tracts ofprivate land is often simple, althoughit can be extremely difficult wherecaves are easily reached on landsopen to the public. Private landown-ers can reestablish millions of bats inlong-abandoned caves by simply pro-tecting them from disturbance, clear-ing overg rown vegetation fro mentrances, plugging artificial miningshafts, or opening closed entrances.

See Appendix II for tips on recog-nizing former bat caves in need ofrestoration and Appendix III for guide-lines on conserving and re s t o r i n gthem.

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of Northern Mexico

Bat caves can be a lucrative part of any property fortunate enough to have one. Besideshunting vast numbers of insects, as this bat flight is doing, the bats’ evening emergences canbe a powerful attraction for tourists.When caves are protected, bats can often be drawnback to sites they abandoned in the past.

Bats of northern Mexico live in awide variety of homes: tre efoliage, Spanish moss, cliff-face

c revices, in woodpecker holes orbeneath loose bark on old snags. Afew even live in erosion crevices orbeneath large rocks. As natural roostshave been lost, several of the moreadaptable species have sought shelter

in human-made structures, such asbridges, road culverts and buildings.

Each species, however, has its ownunique requirements. Red and yellowbats, for example, cannot live incaves, while free-tailed bats cannotlive in tree foliage.

Bats that live alone or in smallcolonies often have the most options

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Cave-dwelling Bats

Where Bats Live

Some bat species need very littleroom to find a home.These westernpipistrelles (Pipistrellus hesperus) foundsnug shelter in a slender rock crevice.

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of Northern Mexico

A silver-haired bat(Lasionycteris noctiva-gans) peers out of itsroost in the hollow ofan old tree (left), whilethe spotted bat(Euderma maculatum)emerges from a com-fortable opening in arock wall (below).

and are least noticed. Those that formvery large colonies in caves are typi-cally the most vulnerable if their tra-ditional roosts are threatened. Often,only a few caves meet large-colonyneeds, and these have been used forthousands of years. They are nowvital to survival.

Bats are part of a complex ecolog-ical system that includes numerouscaves and whole ecosystems from thesouthwestern United States to centraland southern Mexico. We simply donot know what would happen ifeither the bats or an important plantspecies were to disappear, though thepotential for widespread ecologicaland economic harm is sobering.

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Cave-dwelling Bats

These lesser long-nosed bats (top) areperched in a cave, their faces covered withpollen of the plants from which they tooknectar. Even Spanish moss can provide ahome for this western yellow bat (Lasiurusxanthinus).

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of Northern Mexico

Eastern red bats (Lasiurus borealis)roost in the foliage of trees, wheretheir distinctive color disguises themas dead leaves or pine cones.

Even in regions where thousandsof caves exist, relatively fewmake good homes for more

than small numbers of bats. In gener-al, the largest bat colonies are foundin caves with extra large entrancesand passages. The risk of a bat’s beingcaught by a snake, owl, raccoon orother predator is highest when it mustpass through an entrance that is smallor partially blocked by vegetation.Unfortunately, the largest caves alsoattract the most humans.

Mother bats rearing pups mustfind caves with ceilings that are roughenough for babies to cling to andmore than two meters above the floorto avoid jumping predators. Dome-

shaped ceilings are often essentialbecause they trap the bats’ body heat,which helps babies grow faster. Thecooler the climate, the more difficultit is for bats to find roosts that arewarm enough for rearing young, butlarger colonies can warm roosts withtheir body heat.

Male bats normally separate intobachelor groups in summer, living ind i ff e rent caves than the nurserycolonies. Living in separate cavesreduces competition for food at atime when mothers must nearly dou-ble their consumption in order tonurse their young.

In general, caves with more thanone entrance are most likely to trap

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Cave-dwelling Bats

Lives of Cave-dwelling BatsSelecting Homes

A cave must meet certain conditions to accommodate Mexican free-tailed bats, but whenthey find the right cave, vast numbers of these bats will often move in.

w a rmer or cooler outside air. Thosethat slope upward tend to trap warm e ra i r, while the reverse is true for cavesthat slope down.

Because most of nort h e rn Mexicois relatively warm, few caves areknown to be cool enough for bats toh i b e rnate in winter. However, manyof the re g i o n ’s bats do spend the win-ter in cooler caves, where their bodyt e m p e r a t u refalls and they enter a low-metabolism state called torpor to con-s e rve fat supplies during severe weath-e r. If true hibernation caves exist inMexico, they are likely to be found athigh elevations, and they could becritically important to many bats.

Most bat colonies must moveamong several caves through anannual cycle. Even nursery coloniesalmost always move seasonally. Up tohalf a dozen or more caves may berequired by a single large colony.

Bat colonies of northern Mexicothat number over 150,000 are almostalways Mexican free-tailed bats.Colonies of several thousand

to100,000 are more likely to be long-nosed bats or cave myotis (Myotisvelifer), species that are less adaptableand especially vulnerable. Cavemyotis numbers appear to havedeclined alarmingly in many areas,though there is little documentationof its current status.

Approximately a dozen of north-e rn Mexico’s bat species formcolonies of from less than 10 to sever-al hundred individuals. These are thebats most often found in smaller caveswith smaller entrances. Because theycan occupy caves that are less attrac-tive to humans, they tend to be lessthreatened.

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of Northern Mexico

Free-tailed bats emerge eachsummer evening fromBracken Cave in Texas tospend the night hunting flyinginsects.

Not much is known with cer-tainty about bats’ court i n gbehavior, but their approach-

es to attracting mates seem to bequite varied. In some species, malessimply guard a good cavity in a caveceiling, and females select himaccording to the quality of home heo ffers. Among Mexican fre e - t a i l e dbats, males claim special chambers incave ceilings and also sing to lureprospective mates.

As with other animals, some malesare unable to win the attention of anyfemale, while others others attractseveral. Most mating appears to occur

in March. Babies are born in June orearly July.

One pup per year is born to free-tailed bat mothers. Pups are bornpink, naked and about a third of theirm o t h e r’s size. They quickly joindense clusters of other pups, as manyas 5,380 per square meter, hangingfrom cave ceilings. Mothers find andnurse their own pups, despite havingto search among tons of baby bats.Each mother remembers where sheleft her pup, as well as its unique voiceand odor. A free-tailed mother pro-duces more than four times as muchmilk, relative to her body size, as a

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Cave-dwelling Bats

Finding a Mate and Rearing Young

An average of more than 5,000 baby Mexican free-tailed bats are packed into a square meterof cave ceiling, but each mother manages to find her own pup.

Jersey cow.Pups grow rapidly, reaching adult

size and learning to fly and feed inde-pendently in just four to six weeks.Imagine the difficulty of learning tofly in total darkness, navigating withsound alone amidst thousands ofother beginners in a traffic jam whereseveral potentially fatal collisions persecond must be avoided!

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of Northern Mexico

Female bats nursing their young, like thisMexican free-tail (top) and red bat, mustroughly double their food intake to produceenough milk for their rapidly growing off-spring.

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Cave-dwelling Bats

Navigating in the Dark

C ontrary to popular misconceptions, all bats

have eyes and can see as well as other

nocturnal animals. In addition, however, bats can

also navigate in the total darkness of caves by

relying on a sonar-like system known as echolo-

cation. Pulses of sound are emitted through the

mouth or nose, and returning echoes are ana-

lyzed to detect objects as fine as a human hair.

Relying on these echoes, a bat can also find and

capture more than one tiny insect in a single

second, sometimes more than 1,000 in an hour!

Both free-tailed and long-nosedbats are long-distance travelers.Many of them migrate far to the

north each spring and return south-ward in the fall.

Insect-eating bats like the free-tails time their annual cycles to coin-cide with insect abundance alongtheir migration route, while long-nosed species follow a com-plex “nectar trail”of sequentiallyf l o w e r i n gplants in both spring and fall (seeFinding Food and Co-evolving with Plants).

Mexican free-tailed bats are mas-ters of long-distance travel. Eachnight, they climb to just the right alti-tude, sometimes thousands of metersabove ground, to find tail winds thatspeed them to feeding areas morethan 80 kilometers from their caves.

In the fall, when they must travelmuch longer distances, they wait toride storm-front winds that can help

carry them more than 800kilometers in a night. Theytravel in large flocks, appar-ently relying on older,experienced individualsto find their waybetween caves hun-dreds of kilo-

meters apart. How theylocate traditionallyused caves from thousands of metersabove ground remains a mystery.

Little is known about the exactdetails of individual trips, but it isclear that stop-over caves, includingmany in northern Mexico, are essen-tial for migrating bats.

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of Northern Mexico

Traveling Long Distances

Species that formhuge colonies and requiremany tons of insects nightly

must be expert long-distance hunters.Scientists have recently discovere dthat the largest colonies of free-tailedbats live in locations where they canmost easily intercept migrating mothsthat pass each spring and fall. Theyalso rely on long, narrow wings andfind tail winds to facilitate their trav-el, sometimes intercepting vast num-bers of migrating insects literallythousands of meters above ground.

Free-tailed bats apparently scoutlarge areas and have excellent memo-ries and means of communication,because they also are expert at sud-denly appearing in large numbers totake advantage of moths that areeither migrating or hatching from asingle cornfield.

In an attempt to avoid capture,such moths have evolved specialhearing to detect approaching bats.H o w e v e r, as they fly high aboveground to move among crops, or tomigrate long distances, they areextremely vulnerable to fast flyingbats like free-tails. Other bats have awide variety of adaptations for copingwith insect hearing.

C a l i f o rnia leaf-nosed bats(M a c rotus californ i c u s) normally form

colonies of just dozens to hundreds ofindividuals in caves and rely on short ,b road wings that enable helicopter-like flight. By living in smaller num-bers and being more maneuverable,they can occupy much smaller cavesthan free-tails and do not have to trav-el far to find sufficient food. By avoid-ing the need for long, high-speedtravel, they can rely on catchingsleeping insects directly from theg round or vegetation in a manner thatwould be impossible for less maneu-verable free-tails. They also have extral a rge eyes and superb night vision thatenables them to see insects only 4 mmlong without having to inadvert e n t l yw a rn of their approach by emittingecholocation sounds. In fact, theseand pallid bats (A n t rozous pallidus) havehearing so sensitive that they candetect even the faint sounds of a walk-ing cricket or katydid. They rely ontheir hearing rather than on echoloca-tion for their final appro a c h .

Many insect-eating bats haveintermediate strategies. Cave myotishave wings that resemble neither jets

28

Cave-dwelling Bats

Finding Food

SPECIAL ADAPTATIONS

FOR HUNTING This pallid batjust caught akatydid.

nor helicopters, meaning they cantravel farther than leaf-nosed bats, butnot nearly as far as free-tails. Theycan pursue insects faster than leaf-nosed bats, but aren’t as good at hov-ering to pluck them directly fromfoliage. Cave myotis typically huntinsects near trees and shrubs where it’seasier to surprise their prey. By hunt-ing close to cover, they avoid detec-tion, just as police radar surprisesmotorists better when hidden behindhills or around corners.

Bats also have very different adap-tations for dealing with specific kindsof prey. Pallid bats, for example areimmune even to the deadly stings ofscorpions and centipedes. They also

have larger wings for lifting, enablingthem to feed on a wide array of largerp rey for which other bats cannotcompete.

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of Northern Mexico

A centipede is about tobecome a meal for this pallidbat.These bats pluck almost alltheir prey from the ground.

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Cave-dwelling Bats

CO-EVOLVING WITH PLANTS

It is difficult to determine exactly how bats originally began

to feed on nectar and fruit, but they most likely were first

attracted to plant-visiting insects. Pallid bats, which are most-

ly insect-eaters, visit cactus and agave flowers to also feed on

nectar, and insect-eating California leaf-nosed bats eat cactus

fruits, as well. Long-nosed bats and Mexican long-tongued bats

(Choeronycteris mexicana), however, feed almost exclusively on

the nectar of agave and giant cactus plants. Over thousands of

years, these bats and the plants they visit have co-evolved to

become highly interdependent, so much so that loss of either

could now seriously jeopardize the other.

Agaves have developed amutually beneficial relation-ship with bats.The plantsdepend heavily on bats forpollination, while Mexicanlong-tongued bats (thispage) and lesser long-nosedbats (opposite page) feed onthe nectar of agave flowers.

In nort h e rn Mexico, organ pipe,s a g u a ro and cardon cactus – thel a rgest and often the most ecological-ly important plants in their regions –stagger flowering and fruiting times tocoincide with the nort h w a rd migra-tion and re p roduction of bats. Thebats re t u rnthe favor through superiorpollination and seed dispersal for thecactus community.

Later in the season, many speciesof agave plants bloom in a re v e r s esequence that creates “the nectar trail,”which supports the bats with a contin-uously blooming food supply as theymove southward into central ands o u t h e rnMexico. Along the way, thebats are essential pollinators and seeddispersers for those plant communi-t i e s .

This is clearly a complex, inter-

related system involving numero u scaves and whole ecosystems from thesouthwestern United States to centraland southern Mexico. We simply donot know what would happen if thebats or an important plant specieswere to disappear, but the potentialfor widespread ecological and eco-nomic harm is sobering.

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of Northern Mexico

CAV E M Y O T I S

Myotis velifer

Myotis bats are noted for their ratherplain, unspecialized faces. Severalspecies enter caves of northernMexico, but only the cave myotisforms colonies numbering in the tensof thousands.

CALIFORNIA LEAF-NOSED BAT

Macrotus californicus

Huge ears enable bats to hear thefaintest of sounds, even the footstepsof a walking cricket or the munchingmandibles of a feeding caterpillar.Some bats have leaf-like noses theyuse to transmit echolocation soundsthrough their noses. Extra-large eyesenable this bat to navigate and huntby vision alone on all but the darkestnights, when it must rely on echolo-cation.

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Cave-dwelling Bats

Understandingthe Diverse

Faces of

C a v e - d w e l l i n g

B a t s

33

of Northern Mexico

LA R G E F R E E-TA I L E D BAT

Nyctinomops macrotis

These bats’ large, laterally flattened earshelp provide lift for their heads whileflying at high speed. For their body size,they have some of the narrowest wingsof any bat, which permits almost jet-likeflight. Long facial hairs probably helpthem feel their way in narrow rockcrevices. These bats, like other verylarge free-tailed bats, normally roosthigh on cliff faces, from which theydrop to begin flying. They are foundonly in caves that provide high cavitiesabove extra large entrances.

ME X I C A N L O N G-T O N G U E D B AT

Choeronycteris mexicana

Long, slender noses and small earshelp nectar-feeding bats fit theirheads deep into the flowers fromwhich they feed. Long whiskers helpthem feel their way into theflower, and large eyes helporient the bats to theirfavored blooms.

COMMON VAMPIRE BAT

Desmodus rotundus

The pit-like shapes on this bat’s noseare heat sensors that detect areas onan animal where rich capillary sys-tems are near the skin. There thevampire can bite and obtain a meal

with the least pain to the victim.Large eyes also help the bat avoidbeing harmed by the creatures itbites. This bat’s saliva contains a spe-cial anticoagulant that ensures asteady flow of blood. An entire mealtypically consists of just 20-30 milli-liters.

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Cave-dwelling Bats

FU N N E L-E A R E D B AT

Natalus stramineus

This bat’s funnel-shaped earsundoubtedly are part of a highlyspecialized echolocation system.Tiny eyes suggest a heavy relianceon non-visual navigation.

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PE T E R S’S G H O S T-FA C E D B AT

Mormoops megalophylla

Strange faces and small eyes areoften associated with highly sophisti-cated echolocation systems. No oneknows why these bats’ eyes appear tobe located in their ears. The extraflaps of skin around their lips areused to form a horn shape duringflight that helps focus echolocationsounds transmitted through themouth.

TO W N S E N D’S B I G-E A R E D B AT

Corynorhinus townsendii

This bat’s big ears can pick upvery faint insect sounds, butthey may also help regulatebody temperature. When at restin a cave, the bat often curls itsears into a shape resembling aram’s horns. Extending thoselong ears increases the bat’s sur-face area and could help dissi-pate heat.

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Cave-dwelling Bats

Bags filled with bat guano harvested from this Mexican cave are piled into huge stacks.Thisvaluable resource is an outstanding natural fertilizer that is continually renewable if the batsand their cave are protected.

For as far back as records extend,Mexican free-tailed bat guanohas been extracted for fertilizer.

Near San Antonio, Texas, thousandsof tons have been extracted fro mBracken Cave alone, including 200tons in 2002 and 254 tons in 2004.Surveys conducted by Bat Conser-vation International in 2003 and 2004confirm that guano continues to beharvested where sufficiently large batcolonies remain. Current retail salesrange from 2.86 to 12.10 U.S. dollarsper kilo.

Guano harvesting can be done ona sustainable basis, especially at caveswhere the bats normally migrate else-where for a part of each year. It is

important, however, to keep in mindthat careless disturbance of the batsthat produce the guano can quicklyterminate guano production. To besustainable, harvests must be madewhen the fewest possible numbers ofbats are present, never when mothersare rearing young in late spring andsummer.

For details of the dos and don’ts ofsustainable guano harvesting, seeAppendix IV.

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Bat Caves as Sustainable ResourcesGuano Extraction for Fertilizer

When millions of bats live on the ceilings and walls of a cave, they become almost a factoryfor the production of guano in commercial quantities.

Wildlife watching is a rapidly growing industry. People come from allover North America to experience the spectacular emergences of 20million Mexican free-tailed bats at Bracken Cave, near San Antonio,

Texas. And the evening flights of 1,500,000 of these bats from crevicesbeneath the Congress Avenue Bridge in Austin, Texas, add more than 8 milliontourist dollars to the city’s economy each summer.

Bat Conservation International, Texas Parks and Wildlife Department andThe Nature Conservancy of Texas all offer highly popular bat-watchingopportunities at protected locations. And in the private sector, an increasingnumber of ranches in the southwestern United States and northern Mexico areadding to their revenues by attracting wildlife-watching visitors. The specta-cle of an evening bat emergence can be a valuable boost for attracting tourists.

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Cave-dwelling Bats

Wildlife Tourism

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Wildlife is becoming increasingly popular as a tourist attraction, and few things in nature compare inspectacle to the emergence of millions of bats from a cave (above) or from beneath an urban bridge(left) in downtown Austin,Texas. Both these sites are powerful magnets for tourists.

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Cave-dwelling Bats

Do not burn, poison, dynamite oro t h e rwise harm bat caves in

hopes of controlling vampire bats.Such destructive actions are counter-

p roductive, sincev a m p i r e s

d o n ’t need caves to survive and bene-ficial bats are far more likely to bek i l l e d .

L a rge-scale control is bestachieved by corralling livestock forseveral nights before setting “mistnets” around the enclosure and cap-turing incoming vampires. Paste the

bats with a mixture of Vaselineand Chloro p h a c i n o n e

and allow themto return

Appendix I

Controlling Vampire Bats

A p p e n d i c e s

Vampires (below)are easily distin-guished from ben-eficial insect-eat-ing bats (right).

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Controlling vampire bats begins with capturing them with mist nets placed near livestock.Thebats should then be coated with poison and set free to spread the poison. Roosts used byvampires are readily identified by the dark, tar-like droppings of these bats, as opposed to thepellets or powder that is characteristic of other bats.

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Cave-dwelling Bats

Common vampire

to their roosts, where each vampirecan poison up to 40 others as theyhelp groom toxins from the pastedbats’ fur. Captured vampires must betreated and released – not killed – orthe procedure will fail.

To eliminate harm to individualdomestic animals, paste their vam-pire-bite wounds with the same mix-t u re in late afternoon or earlyevening. Returning vampires will bepoisoned, since they typically try toreopen previous wounds to feed.

Small numbers of pigs, chickens

and other domestic animals may bemost easily protected by simply pro-viding them with vampire - p ro o fenclosures. These should contain noopenings of more than a centimeter indiameter.

For detailed advice, visit BatC o n s e rvation Intern a t i o n a l ’s onlinecatalog – w w w. b a t c a t a l o g . c o m – ando rder a copy of the C o n t rol delMurciélago Vampiro y la Rabia Bovinavideo.

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Ranchers (left) paste a toxic mixture ofVaseline and Chlorophacinone on a capturedvampire bat.They will release the bat toreturn to its roost to poison as many as 40other bats as they help groom the pastedbat.Vampires (above) make a tiny wound thatthe victim often does not even feel, thenchemicals in the bat’s saliva increase the flowof blood.

When looking for old bat roosts,first check caves with larg e

(especially more than thre e - m e t e r )entrances and interior dimensions.These typically shelter the largest batcolonies.

Inside a cave, look for clues batsleave behind after long use of the site.Dark-brown or rusty-red stains onlimestone surfaces, especially ondomed, heat-trapping ceilings, indi-cate where bats have roosted.

Examine the floors beneathdomes, especially stained ones, forevidence of old bat droppings. Thesemay still be pellets, but could alsoremain only in powder form. Bat

droppings, unlike those of rats ormice, are easily crushed and sparklewhen lit due to shiny fragments ofinsect wings and bodies. Reddish tonearly black, tar-like dro p p i n g s(never in pellets) are left only by vam-pires (see page 41). Nectar bats tend toleave yellowish splats on walls.

You can estimate former numbersby measuring the number of squaremeters that were probably covered byroosting bats (based on stained lime-stone and/or droppings) and multi-plying the area times 2,000 bats persquare meter. That’s roughly the aver-age roosting density of adult free-tailed and myotis bats in northern

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Cave-dwelling Bats

Appendix II

Recognizing Former Bat Roosts in Caves

This thick coating of guano on the floor of a cave provides unmistakable proof that bats areusing or have used the cave for some time.

Mexico.R e p o rtbat caves that need help to

Bat Conservation Intern a t i o n a l ,Mexico Program Coord i n a t o r, Dr.A rnulfo Moreno (l e p t o n y c t e r i s 2 0 0 0 -@ y a h o o . c o m . m x), or visit BCI online atw w w. b a t c o n . o rg. Mailing address: BatC o n s e rvation International, PO Box162603, Austin, Texas 78716 USA.

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The rusty-red stain on the ceiling and walls of this cave was caused by many years of roosting bycountless bats. Most abandoned the cave long ago, but many are returning after Bat ConservationInternational removed brush from the entrance.

Here are some critical guidelinesfor protecting bats that use

caves:■ Avoid repeated or prolonged distur-

bance of roosting bats, especially inspring and summer.

■ Prevent fires or the use of fireworksin or near cave entrances.

■ Never allow use of internal-combus-tion engines inside caves.

■ Do not enlarge or reduce caveentrances or dig new openingswithout first consulting a bat expert.

■ Trim encroaching trees or othervegetation from cave entrances.

■ Route heavily used roads away fromcave entrances.

■ Minimize use of pesticides at timesand places were they are most like-ly to harm bats, especially in areaswhere bats feed. Spraying crops atdawn is least likely to contaminateinsects that are eaten by bats.O rganochlorine, org a n o p h o s p h a t e

and carbamate insecticides can poseserious threats to bats, and synthet-ic pyrethroids may.

■ Entrance gates can help protect batsf rom human disturbance, butMexico’s largest bat colonies areunlikely to accept them unless aspace at least 2 to 3 meters tall canbe left open above the gate so batscan enter and exit freely along theentrance ceilings. (For gating detailscontact Bat Conservation Inter-national.) Posted fences may be use-ful in some instances if they do notobstruct the bats’ flight path.

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Cave-dwelling Bats

Appendix III

Guidelines for

Conserving Cave-dwelling Bats

Guano can be harvested profitablywithout harming the bats that

provide this valuable resource, if you:■ Permit guano extraction only when

few or no bats are present, typicallyin winter.

■ Avoid obstructing cave entrances ordigging shafts. Obstructions cangreatly increase risks from preda-tors, while new shafts or changes inentrance size can change roost tem-peratures. Either result can forcebats to abandon the cave.

■ Never permit fire in or near caveentrances. Smoke can enter and suf-focate bats, and the guano can catchfire and burn for months.

■ Never use intern a l - c o m b u s t i o nengines or kerosene torches in batcaves. Oxygen can be depleted, and

fumes can kill bats and humans inthe enclosed space.

■ Reduce health risks to workers byproviding respirators capable of fil-tering dust particles down to onemicron in diameter and changingfilters daily.

■ Always keep extracted guano dry.Wet guano may lose its commercialvalue.

■ Avoid being defrauded by unscrupu-lous guano miners/buyers. Checkre f e rences and proof of re q u i re dgovernment permits before signingcontracts.

■ Collaborate with other guano caveowners to identify problems ande n s u re better pricing. Bat Con-servation International is preparinga list of owners and buyers and isavailable to assist.

■ Prior to allowing removal of guanofrom premises, ensure that paymentis guaranteed and that all extractionequipment and trash is re m o v e df rom the cave and surro u n d i n gp ro p e rty (including scaff o l d i n g ,wires or other possible obstructionsto bat flight).

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Appendix IV

Precautions for

Sustainable Guano Harvesting

With a little care, guano harvesting can con-tinue at caves like this one long into thefuture, although blocking a passage, as seenhere, can force bats to abandon the cave.

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Arita, H.T. “Conservation Biology of the Cave Bats of Mexico,” Journal of Mammalogy (1993). 74:693-702.Arita, H.T. y Martinez del Río. “Interaccíon Flor-Murciélago: Un Enfoque Zoocéntrico,” Publicaciones

Especiales del Instituto de Biología. Universidad Nacional Autónoma de México (1990). 4:1-35.Arroyo, J.C., y T. Alvarez Restos Oseos de Murciélagos. Instituto Nacional de Antropología e Historia:

México, D.F. (1990).Baker, R.H. “Mammals of Coahuila, Mexico,” University of Kansas Publications. Museum of Natural History:

Lawrence, Kansas (1956). 9:125-335.Brunet, A.K., and R.A. Medellín 2001. “The Species Area Relationship in Bat Assemblages of Tropical

Caves,” Journal of Mammalogy (2001). 73:365-378.Clark, D.R., Jr., A. Moreno-Valdez and M.A. Mora. “Organochlorine Residues in Bat Guano from Nine

Mexican Cave Roosts, 1991,” Ecotoxicology (1995). 4:258-265.Cockrum, E.L. “Migration in the Guano Bat, Tadarida brasiliensis,” Miscellaneous Publications. Museum of

Natural History: Lawrence, Kansas (1991). 51:303-336.Cockrum, E.L. “Seasonal Distribution of Northwestern Populations of the Long-nosed Bats, Leptonycteris

sanborni family Phyllostomidae,” Anales del Instituto de Biología, Universidad Nacional Autónoma deMéxico (1991). 62:181-202.

Des Marais, D.J., J.M. Mitchell, W.G. Meinschein and J.M. Hayes. 1980. “The Carbon IsotopeBiogeochemistry of the Individual Hydrocarbons in Bat Guano and the Ecology of the InsectivorousBats in the Region of Carlsbad, New Mexico,” Geochimica et Cosmochimica Acta (1980). 44:2075-2086.

Fleming, T.H., A.A. Nelson and V.M. Dalton. 1998. “Roosting Behavior of the Lesser Long-nosed Bat,Leptonycteris curasoae,” Journal of Mammology (1998).

Geluso, K.N., J.S. Altenbach and D.E. Wilson. 1976. “Bat Mortality: Pesticide Poisoning and MigratoryStress,” Science (1976). 194:184-186.

Glass, B.P. “Seasonal Movements of Mexican free-tail bats Tadarida brasiliensis mexicana Banded in the GreatPlains,” Southwestern Naturalist (1982). 27:127-133.

Hall, E.R., and W.W. Dalquest. “The Mammals of Veracruz,” University of Kansas Publications. Museum ofNatural History: Lawrence, Kansas (1963). 14:125-335.

McNab, B.K. “Energetics and the Distribution of Vampires,” Journal of Mammalogy (1973). 54:131-144.McCracken, G.F. 1986. “Why are We Losing our Mexican Free-tail Bats?,” BATS (1986). 3(3):1-4.McCracken, G.F., and J.K. Westbrook. “Bat Patrol: Scientists Discover that High-flying Mammals are Bad

News for Bugs,” National Geographic (2002). 201(4):114-123.Medellín, R.A., H.T. Arita y O.H. Sanchez. 1997. Identificación de los Murciélagos de México. Associacion

Mexicana de Matozoologia, A.C.: Mexico, D.F. (1997).Mizutani, H., D.A. McFarlane and Y. Kabaya. “Nitrogen and Carbon Isotope Study of Bat Guano Core

from Eagle Creek Cave, Arizona, U.S.A.,” Mass Spectroscopy (1992). 40:57-65.Mizutani, H. “Carbon and Nitrogen Isotopic Signatures of Bat Guanos as Record of Past Environments,”

Mass Spectroscopy (1992). 40:67-82.Moreno-Valdez, A. Ecological Studies of the Mexican Long-nosed Bat (Leptonycteris nivalis). Dissertation, Texas

A&M University: College Station, Texas (2000).Moreno-Valdez, A. Murciélagos de Nuevo Leon: Nuestros Invaluables Aliados. Impresora Monterrey: Monterrey,

Nuevo Leon (1996).Tuttle, M.D. “The Lives of Mexican Free-tailed Bats,” BATS (1994). 12(3):6-14.Villa, B., and E.L. Cockrum. “Migration in the Guano Bat Tadarida brasiliensis mexicana,” Journal of

Mammology (1962). 43:43-64.Watkins, L.C., J.K. Jones and H.H. Genoways. Bats of Jalisco, Mexico, (Special Publications). The Museum,

Texas Tech Press: Lubbock, Texas (1972).Wilson, D.E. Murciélagos Respuestas al Vuelo. Universidad Veracruzana, con licencia de Smithsonian

Institution: Xalapa, Veracruz (2002).

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Suggested Reading and Resources

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Bat Conservation International is the world leader in protecting bats and their habitatsand in educating the public about the many benefits of these remarkable and misun-derstood animals. Please join us in this effort. Visit our website, www.batcon.org, forinformation or to become a BCI member.

PO Box 162603 • Austin, Texas USA 78716 • 512.327-9721

DR. MERLIN D. TUTTLE, Founder and President of BatConservation International, has been studying and protectingbats and their habitats for more than 40 years. His knowledgeabout these remarkable animals is unsurpassed.

DR. ARNULFO MORENO, Associate Professor atTechnological Institute of Ciudad Victoria in Tamaulipas, hasstudied the bats of northern Mexico for 15 years and is a lead-ing authority on cave-dwelling bats of the region.