JOURNAL OF APPLIED ANIMAL WELFARE SCIENCE, 2(3), 169-186Copyright @ 1999, Lawrcnce Erlbaum Associates, Inc

Influences on the Feeding Behavior ofThree Mammals in the Maruyama Zoo:

Bears, Elephants, and Chimpanzees

Naruki MorimuraHayashibara Museum of Natural Sciences

Yoshikazu UenoCenter for Experimenml Plants and Animals

Hokkaido University

Modifications of feeding conditions are essential to the establishment ofenvironmen-tal enrichment in zoos In this study, we attempted to increase the duration offeedingby varying fetding conditions, such as the spatial or temporal distribution of foods,while kerping the solts and amounts of food the same Subjects included nonhumaranimals reared at the Maruyama Zoo in Sapporo, Japan: 3 bears ( Urs us arctos),2 ele-phafis (Elephas taxim6), and 5 chimpanze€s (Pan troglod)tei) Considering thatthe feeding ccologies of these animals differed a great deal f.om those in the wild, weused the focal animal sampling method Consisting of the spatial dispersive andmassed feeding conditions, the experiment with bears found feeding time increasedmore in the dispersive condition In addition, the b€havioral rhythm of altemate feed-ing and sleeping appeared The experiment with elephants, consisting of the temporaldispersive and massed condition, increased fe€ding time under the massed conditionThe experiment using chimpanzees reversed conditions used in the elephant studyand increased feeding time under the dispersive condition Results indicated thatthese simple modifications both influenced an increasing duration of feeding and af-fected behavioral pattems in a day

Environmental enrichment has created considerable interest worldwide in recentyears, especially in Westem zoos concerned about nonhuman animal welfareand species preservation Environmental enrichment seeks to approximate the

Requesls for reprints should be sent to Naruki Morimura, Hayashibara Museum of Natural Sciences,Shimoishii l-2-3, Okayam4 700-0907, Japan E-mail: narukim@rc4 so-net nejp

170 MORIMURA AND UENO

behavioral repertoires and activity budgets of animals in a zoo with that of ani-mals in the wild We observed nine mammalian species at three zoos in Japan

and compared behaviors among species, seasons, and exhibit conditions Tbese

observations suggested that large differences in behavior existed between these

zoo animals and their wild counterparts (Morimum & Ueno, 1998) Zoo animalbehavior, lacking much of the natural behavioral repertoire and/or distorted inthe time budget, appears monotonous, especially with respect to feeding Gen-erally, wild animals spend more than half the day feeding Thus, to accomplishenvironmental enrichment in zoos, it is important to make the time budgets offeeding behavior similar to those of the wild

Significant efforts were made to promote feeding enrichment in zoos For-aging boards and puzzle boxes were developed, and their effectiveness in feed-ing-time prolongation for nonhuman primates was examined (Reinhardt &Roberts, 1997) Attempts were also made to reduce the level of abnormal behav-iors in bears, by modifying the presentation of foods (Fonhman et al , 1992)Few studies, however, referred to the effectiveness of enrichment on other be-

havioral repertoires and activity budgets during the day The aforementionedstudies emphasized the effectiveness of modifying feeding conditions on stereo-typed behavior Because few studies direcdy compared the behaviors of zoo ani-

mals with that of their wild counterlarts, what is more important in making thefeeding behavior of zoo animals similar to that of wild animals-food type vari-ation or presentation-is unclear.

Many zoos carry out food provisioning once or twice a day, and the variety offoods is limited Day to day, the time of such provisioning usually remains thesame In the wild, however, food resources are usually dispersed over the animals'habitat Diurnal species frequently engage in feeding and exploration activitiesduring the day In general, feeding behavior has several peak periods during thedaytime, and some species have a feeding rhythm These differences in feedingconditions between the zoo and the wild very likely affect not only the features offeeding behavior itself, but also those of other behaviors These experiments at-tempted to €xtend the length of time zoo animals engage in feeding and foragingbehavior by modifying various feeding conditions Examples included changingthe spatial distribution of foods in the exhibits (dispersive vs massed), and thetemporal distribution of food provisioning (small amount-high frequency vs. largeamount-low frequency), while keeping the food types and the amounts constantWe examined quantitatively the influences on behavioral repertoires and activitybudgets in a day

At the Maruyama Zoo, we observed three species whose respective feedingecologies are different in the wild: bears (Ursus arctos\, elephants (Elephas

maximus), zndchimpatzees (Pan toglodyres) Bears, whose exhibit sizewas rela-tively large (306 m2), were surveyed for the influence of the spatial distribution offood Elephants and chimpanzees, whose exhibits were relatively small (68 m2 and

FEEDING BEHAV:ORS 171

42 m2, respectively), were surveyed for the effects of food provisioning frequency(temporal food distribution).

EXPERIMENT 1. BEARS

The experiment consisted of the spatial dispersive feeding eondition (D condi-tion) and the spatial massed feeding condition (M condition) In the D condition,cloter (Trifulium repens), one of the conyentional food items of summer, wasscattered over the entire area ofthe exhibit In the M condition, the same amountof clover, to be shared among three individuals, was laid out in three locationsBy comparing the animals' behavior in the two conditions, we examined the ef-fectiveness of the modification on various behaviors and on the prolongation offeeding time

Method

Subjects. Subjects included 3 brown bears one male bear designated "No1," 38 years old, and 2 female bears designated "No 2" and "No 3," 24 years oldand 15 years old, respectively, housed together at Maruyama Zoo They were keptin an outdoor exhibit (306 m2) thoughout the year, except for periods of foodprovisioning in the moming The outdoor enclosure was an open-field style exhibitwith a concrete surface During the summer, when this experiment was conducted,vegetables, fish, and meats were provided in the moming at the indoor cage At theoutdoor exhibit, each bear received a whole chicken In the aftemoon, clover wasprovided at the outdoor exhibit

Procedure. The l8-day experiment was conducted in 1996 between Septem-ber 20 and October 9, excepting October 4 and 6 Only the way that clover wasprovisioned was modified between the two conditions All other conditions werek€pt constant In the D condition, cloverwas scattered over the entire exhibit In theM condition, clover was provided at three locations only The experiment was con-ducted for five l-hr periods per day Periods began at 9:30 a m , 12 00 p m , l:15p m,2:30p m ,and3 45p m Each condition wascontinued for 3 consecutivedaysWe began the experiment with the D condi tion and repeated the two conditions alter-nately thrce times (D, Ml D,M; D, M), yieldingarotal of 18 sessions Duringtheex-periment, food provisioning occuned in the morning between 10:00 and l l:00 a mClover (5 kg) was proyided in the afternoon between 3 @ and 4 00 p m Indoor andoutdoor distribution of food was 527o (12 kg) and 48Vo (1 I kg), respectively

172 MoRTMURA AND uENo

We used a focal animal sampling method (Altmann, 1974) and categorized be-havior by using the ethogram from a former study (Morimura & Ueno, 1998) Theethogram corsisted of 47 behavioral categories based on the posture of animalsand the function estimated by motor patterns such as feeding, resting, attack, andplay (see Table 1) The data included these 47 behavioral categories and the timeswher each appeared and disappeared Based on higher functional aspects of theanimals' behavior, such as survival, reproduction, and social interacti.on, the 47behavioral units were divided into six behavioral pattems:

I Primary behavior (PB)2 Locomotion3 Social interaction4 Search (SR)5 Comfort behavior6 Context-free behavior (CFB)

Data were analyzed for the time budgets of each behavioral pattem in a day, thetypes of behavioral units that each behavioral pattern contained, and the temporalpattems of these behaviors during a day

TABLE 1

Definilion of gehavior Types and Repe.toires

Behlrviot Tlpe Delnition (Behavior Repe oites)

Primary behavior Behaviors that sustain life and r€prcduction (e I , feeding, drinking,resting, sle€ping, sexual behavior, excretion, disorder, seating, rearingoffspring)

Incomotion Spatial change from ooe place lo anoth€r place (e g , walking, ruoning,moving backwards, jumping, climbing, hanging, swimming)

Social inreraction Relationships among t*o or more iodividuals (e g , socia.l grooming, socialplay, attack-I., attack-2b, avoidance, body contact, keeper interaclion,visitor interaction, social vocalization, social consp€cific exploration,social heterospecifi c exploration)

Se.rching Using of sense orgaDs (e g , direct objec( searching, listeniog, sniffing,staring, fixation)

Comfort behavio Self-dirccied behavior (e g , self-grooming, body maDipulation, checking,

strEtching, shaking, licking, yawning, involuttary rcaction, bathing)Context-free behavior Behavior with no clear function (e g , obFct rnanipulation, body

manipulation, stereolypic locomotion, stereotypic action, impulsivemoverne[t, vocalizdion)

.Attack- I is an aggre.ssive intemction which does not clear the dominance-subordinrnce rElationshipbAttack-2 is an aggressive interaction which does clear that reladonship

FEEDINC BEHAVIORS 173

Results

In the D condition, some cloyer was still ayailable, after more than 4 hr, until theend of the fifth period-at least from the third period, when the clover was pro_vided On the other hand, in the M condition, bears consumed almost all of theclover during the founh period, only about l% hr after food provisioning. By theend of the fifth period, all remaining clover was eaten This tendencv was ob-served in every session

In the case of the duration ofPB and CFB, the difference between the two con_ditions markedly appeared at and after the third period Individual differences inbehavior were small. The duration of PB in the third and fourth periods in the Dcondition was 83 ad 96Vo, respectively In the M condition, the correspondingfigures were 52 and 59% The total duration ofPB in the D condition was I 3 timeslonger than in the M condition (Figure I ) CFB in the D condition had almost dis-appeared at and after the third period In the M condition, CFB appeared during allfive periods, an average of l6Ea pet day. CFB in the D condition tended to be ofshorter duration than in the M condition, No l:r(9)=2591 ,p= O!|Z;No 2 t(9)=3 238, p = .0122;No.3i t19) =3 628, p = 0055 The differences between the twoconditions were also evident in the behavioral units, feeding and sle€ping, thatconstituted PB (Figure 2) The duration offeeding per day was l3Zo in the D condi_lion and 4Vo in the M condition Thus, the dispersive way of food provisioningmade feeding time longer than did the massed provisioning In the D condition, thefeeding time significantly increased at the third period, and intermittent feedingwas observed until the fifth period In the M condition, however, feeding had al-most completely disappeared by the fifth period (an average of I 6Zo). In the Dcondition, the duration ofsleeping significantly increased in the fourth period, Nol:(16)=5174,p< 0001;No 2tt('16)=49(f,,p= 0002; No. 3: ( l6) = 4 47 t, p =0004 This indicated that the dispersive way of food provisioning not only pro-

longed the feeding time, but also brought about the spontaneous appearance of abehavioral rhythm in which feeding and sleeping occurred alternately Thisrhythm continued to be observed until the fifth period

Discussion

Dispersive food provisioning accounted for three main features of the bears' be-havior: (a) The amount of feeding time increased, (b) CFB disappeared after theclover provisioning, and (c) an alternating rhythm of feeding and sleeping spon_taneously appeared This rhythm continued for a number of hours until the endof the fifth period It is noteworthy that the rhythm of fe_eding and sleeping oc-cuned spontaneously. In the D condition, an increase in duration was observed

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not only in feeding but also in sleeping The decrease in the duration ofCFB re-sulted from the modification of the way that food was provided, which in turntransformed the time budgets of each behavior Craighead, Sumner, and Mitch-eU (1995) pointed out that brown bea$ in the wild remain in favorable habitatsfor a few days at a time and enter a cycle of feeding and resting

The behavioral rhythm of feeding and sleeping that appeared in this expedmentmay be assumed to be similar to that found in the wild With regard to the prolon-gation of feeding time and the appearance of a feeding and sleeping rhythm, thedispersive food provisioning method allowed us to approximate the behavior ofcaptive beals to the behavior of bears in the wild Even in the D condition, how-ever, the duration of feeding was a third or less of that in the wild Moreover, thebehavioral change in the D condition did not carry over to the next morning Thebehavior before moming food provisioning did not differ significantly betweenthe two conditions To make the duration of feeding time as long as possible-andpreferably close to tiat of the wild-we should consider aspects of the feedingcondition other than the spatial distribution of food

EXPERIMENT 2: ELEPHANTS

The experiment consisted of the temporal massed feeding condition (M condi-tion) and the temporal dispersive feeding condition (D condition) In the M con-dition, all food was provided at one time. In the D condition, food was providedtwice a day without changing the sort and the amount of food between the twoconditions In comparing behaviors observed in the two conditions, we exam-ined the effectiveoess of this modification on zoo animal behavior and on theprolongation of feeding time

Method

Subiects. Subjects included two adult female Asian elephants, 29 and 41

years old, housed together at Maruyama Zoo In the summer, they were kept in the

outdoor exhibit (233 m'?) from 9 0O a m to 3 0O p m without food provisioningDuring the winter, when this experiment was conducted, they nonnally remainedinthe indoor exhibit (68 m,) almost all day, excepting about I hr from 9:00 to 10:00

a m Both exhibits were in an open-field style with a concrete surface Hay, com-rnercial biscuits, and bran were provided once a day when individuals entered the

indoor exhibit at 10 00 a m

FEEDING BEHAVIORS 177

Procedure. The experiment was conducted for l5 days in 1996, fiom Febru-ary 6 to 20 In the D condition (food provision twice daily), the fint provisioningtook place between 9 30 and 10:30 a m (first period) and the second between 3 00and 4:00p m (fourth or fifth period) Food provided in the first provision was 667oof the total weight and included 38 kg of hay, compound feed, and bran, leaving34% ofthe total weight,20 kg ofhay only, for the second provision In the M condi-tion (food provision once daily), all foods were provided at one time, sometime be-tween 9:30 and 10:30 a m We began the expe ment with the D cordition and re-peated the two conditions alternately for a total of l5 sessiols: D condition repeatedthree times, M condition repeated two times The ethogram and the procedure ofobseryation and data analysis were the same as those in Experiment l, except forthe starting time of each period (9:30 a.m, 10:45 a m, I :00 p m, 2:15 p m, and3:30pm)

Results

In the D condition, all foods were completely consumed by the start of the thirdperiod (1:00 p m ), about 3 hr after the first food provisioning Subsequently, un-til the time of the second food provisioning (3:00 p m ), elephants ate nothingfor approximately 2 hr In the M condition, however, elephants had food avail-able to them at all times, from directly after food provisioning (10 00 a m ) untilthe fifth period (3:30 p m ) Foods were completely consumed by the end of thefifth period, about 6y2 tr after food provisioning This tendency was observed inevery session

The marked differences in behayior between the two conditions concemed theduration of PB (feeding), SR (gazing and sniffing), and CFB (stereotyped action)at and after the third period (Figure 3) The behavior of both groups showed thistendency In the third and fourth periods ofthe D condition, the average duration ofPB decreased 47 and 26Vo, respectively The duration of SR, 5l and 587o, andCFB,25 and 387o, increased In the M condition, however, PB occupied an aver-age of gzqo of the animals' time at and after the second period Other behaviorsrepresented only a small proportion, an average of 1070 combined for all five be-havioral types except PB Overall, the duration of PB was 647o in the D conditionand 857o in the M condition Feeding time decreased in temporal disprrsive foodprovisioning where the amount of food per food provisioning was decreased andthe frequency of food provisioning increased In the D condition, when the secondfood provisioning was carried out at the fifth period, the time of PB increasedagain, and the time of SR and CFB decreased Furthermore, even in the M condi-tion the duration of PB continued to decrease, and the duration ofSR and CFB con-tinued to increase as time elapsed from the first period to the fifth At the sametime, the behavioral repenoire ofCFB in the fifth period was different from that inall other periods In the fifth period, the behavioral repertoire of CFB included

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FEEDING BEHAV10RS 179

striking one's own legs or body with hay that served as food (body manipulation)During all other periods, CFB was characterized by swinging one's own head,body, or both from side to side (stereotyped action).

Discussion

The increase in the frequency of food provisioning caused changes in the ele-phants' behavior We drew two conclusions: (a) To increase the total duration offeeding in a day, decrease the frequency of the food provisioning; and (b) PBappears mainly during periods when animals have access to food, whereas SRand CFB are most prominent, and PB disappears almost completely, duringtimes offood unavailability In the D condition, no food was available for about2 hr from the third period until the end ofthe fourth At the same time, the dura-tion of SR and CFB incrcased in the third and fourth periods Based on this,times of food unavailability, hought about by decreasiDg the amount of food pereach round of food provisioning, affected the increase of SR and CFB time Forelephants, the fluctuations of SR and CFB time correlated closely with that ofPB. This study showed the importance of maintaining the consumption of foodsfor elephants rather than increasing the frequency of feeding, which results inderreasing the amount of food per food provisioning

Even in the M condition, the same behavioral change in the case of food un-availability occu[ed toward evening. The duration of PB decreased, and that ofSR and CFB increased In the fifth period in the M condirion, animals had con-sumed almost all the food We may consider the possibility that rhe lack of foodprimarily affects the behavioral change During times when the duration ofPB wasmaintained at over 807o per period, the types of behavioral units ofCFB were dif-ferent ftom those observed during other periods Based on these results, we maysay that the elephants' attention to fod became weaker They were satiated Feed-ing behavior in zoos where animals eat foods off the ground includes only simpleconsuming Feeding behavior in the wild, however, includes a large behavioralrepertoire, especially the detailed manipulation of objects for feeding such as

breaking the trunk off a tree, picking leaves off a branch, and removing soil fromthe roots ofa plant (Sukumar, 1989) Compared with feeding behavior in the wild,the fading repertoires ofthe captive animals were poor For this reason, it may benecessary to conduct further €xperiments that focus on bringing out new reper-toires of feeding behavior by modifying feeding conditions and also to examinethe effectiveness of these modifications on the behavior of zoo animals

EXPERIMENT 3: CHIMPANZEES

The experiment consisted of the temporal massed feeding condition (M condi-tion) and the temporal dispersive feeding condition (D condition) In the M con-

180 MORIMURA AND llENO

dition, same as the animals' summer food provisioning routine, all food was pro-vided at one time, sometime during the afternoon In the D condition, whichcorresponded to winter food provisioning, food was given twice a day, once inthe moming and once in the aftemoon By comparing the animals' behavior inthe two conditions. we examined the effectiveness of this modification on zooanimal behavior and on the prolorgation of feeding time

Method

Subjects. Subjects included 5 chimpanzees, selected from a group of 10,

who were housed together at the Maruyama Zoo: one 23-year-old male chimpan-zee designated No l, and four female chimpanzees designated No 2, No. 3, No 4,and No 5, ages 23, 18,20, and 18, respectively Dudng the winter, when the experi-ment was conducted, they were kept in an indoor exhibit (42 mr) all day long Thisexhibit was cage style The ceiling and the wall on the visitor's side were coveredwith grid, and the floor and the walls on all other sides were covered with concreteFurthermore, a glass partition separated the visitors from the chimpanzees Duringthe summer, they were kept in an outdoor exhibit ( 177 mr) from 9:30a.m until3:30p.m In winter, food provisioning was normally carried outtwice aday Vegetables(carrots, cabbages, and greens) and grains (wheat) were supplied in the morningFruits (oranges and apples) and vegetables (greens) were given in the evening

Prccedure. The experiment was conducted for 15 days in 1996, from De-cember 9 to 23. In the D condition (food provision twice daily), the firstprovisioning took place between 10:00 and I I 00 a m. and the second at about 3:00p m Food proyided in the first provision was 45% oftotal weight (10 kg), leaving5570 ofthe total weight (12 kg) for the second In the M condition (food provisiononce daily), all food was provided at one time in the afternoon, 3:00 p m As theconventional frequency of chimpanzee food provisioning in winter was twice aday, a routine opposite of that used for Asian elephants, we began this experimentwith the M condition and repeated the two conditions altemately for a total of 15

sessions: M condition repeated three times, D condition repeated two times Theethogram and the procedure ofobservation anddataanalysis were the sam€ as thoseused in Expedment 1 Only the starting time of each period varied (9 :30 a m, I 0:45a.m, 12:00 p m, l:15 p m, and 2:30 p m )

Results

In the D condition, food was available for about 5 hr after the fint food provi-sion, until the end of the observation In the M condition, some food remained

FEEDING BEHAVIORS 181

for about % hr, at least during the period when foods were supplied The sametendency was observed in all sessions, Marked differences in behavior betweenthe two conditions occurred only in the third pedod (Figure 4) Moreover, thesedifferences varied among individuals In the case of two individuals, No 2 andNo 3, CFB duration decreased significantly in the third period of the D condi-tion, No 2 ,(13)=3.028,p< 001;No 3: t(13)=21't5,p< 05 Two more in_dividuals, No 4 and No 5, showed the same tendency, even though in theircases the differences were not significant For No l, the difference in behaviorbetween the two conditions was marked for the behavioral repertoire of pB Inthe D condition, sleeping time significantly decreased in the third period, (13) =3 308, p < 01 (Figure 5). On average, among the five individuals feeding timewas 77o in the M cor,dition and 24Vo in the D condition As a result of the modi-fication, feeding time increased when the frequency of food provisioning was in-creased and, at the same time, the amount of food per provision was decreasedIn all sessions of the D condition, feeding behavior appeared in all four periodsfollowing the beginning of the second period (Figure 5) The chimpanzees didnot completely consume all the food at one time but fed on it intermittently Inthe D condition, feeding time in each period differed from individuat to individ-ual There was a general tendency, however, for feeding time to decrease afterthe first food provision in the second period and to incrcase again after the sec-ond provision

Discussion

The modification of increasing the feeding frequency determined three main in-fluences on the chimpanzees' behavior:

I Feeding time increased along with the increase in the frequency offeeding2 Differences in behavior that appeared as aresult ofincreasing thefrequency

of feeding continued to be observed for about 2 lII after the first food provi-sion

3 Differences in behavior between the two conditions varied among the fiveindividuals

The main change in behavior in the D condition occurred in the third periodonly. However, feeding behavior was observed in all periods following food pro-vision This indicates that chimpanzees continued to eat intermittently. In otherwords, at times they engaged in behaviors other than feeding, even though foodwas readily available Thus, the modification ofactivity budgets as a whole, due toa change in duration of single bouts offeeding behavior, caused the differences inbehavior in the D condition, not a decrease in sleeping or CFB time and not astraightforward increase in feeding time

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On the other hand, the failure of the animals to pay attention to food despite

its availability indicates the difficulty in increasing feeding time by simply in-creasing the opportunity to feed Yanagihara, Matsubayashi, and Matsuzawa(1994) pointed out that, although controlling a maximum food intake is rela-

tively easy, elevating the food intake of animals in captivity should be more dif-ficult Several studies demonstrated that numerous species readily gather foodfor eating, process food for eating, or both (R€inhardt & Roberts, 1997) A lackof opportunities to engage in these behaviors is conducive to the development ofbehavioral disorders (Hediger, 1955) Moreover, the preserce of another individual might play an important role in stimulating an individual to eat (social fa-cilitation). We may, therefore, encourage individuals to eat by controlling the

social situation during feeding. In addition, we need to examine the effective-ness of the provisioning methods----considered an aspect of food gathering orfood processing-and to adjust social relationships indirectly to promote socialfacilitation in feeding

GENERAL DISCUSSION

These results, although gathered from a small sample of individual animals un-

der conditions present only at the Maruyama Zoo, suggest that the modificationof feeding conditions (spatial and temporal food distribution) increases the dura-tion of feeding, at least in the case of these three mammalian species As feedingtime inoeased, the duration of CFB in bears, that of SR and CFB in elephants,

and that of CFB or sleeping in chimpanzees decreased After a food provision,

elephants continued to eat until all food was completely consumed This sug-

gests that increase in feeding time resulted in a decrease of SR and CFB timeBears and chimpanzees did not continuously eat food when it was availabl€ In

the case of bears especially, the rhythm of alternate feeding and sleeping appeared

spontaneously That is, the duration ofCFB in bears and chimpanzees decreased

because of a tendency not to engage in a behavior such as CFB or sleeping----even

at times when the animals were not feeding-not from simple replacement by the

increase in feeding timeIn this study, the modification of feeding conditions affected not only the tar-

get behavior but also a variety of other behaviors This frnding indicates the im-portance of considering animal behavior from a discerning viewpoint to carryout environmental enrichment The effectiveness of our modiltcations on feed-

ing behavior differed considerably among the tluee species The modificationresulted in a change of feeding patterns in bears and chimpanzees from a "con-suming all food at one time" to an "intermittent feeding with several peak times"

scheme Field studies of bears (Craighead et al , 1995) and chimpanzees

(Goodalt, 1986) observed that feeding and some other behavior are repeated pe-

FEEDING BEHAVIORS 'I85

riodically In this study, the cyclical rhythm of feeding and sleeping in bears oc-cuned yoluntarily under the condition in which foods were dispersed around theanimals'exhibit

Another study reported that Japanese macaques (Macc ca fuscata) in captivityshowed a rhythm of feeding under the condition in which individuals could feedfreely (Mori, 1979) In our study, chimpanzees and bears repeatedly shifted be-tween feeding and another behavior such as resting Hence, when frequency offood provisioning was increased and accompanied by cyclically repeated bursts offeeding, the weakness of feeding drives probably caused the prolongation of feed-ing time in chimpanzees and bears On the other hand, Asian elephants in the wild,similar to other herbivores, especially grazers, spend about 12 to 19 hr a day onfeeding, although some studies reported that a peak time of feeding appears in theevening (McKay, 1993) The duration of feeding was longer in the continuousfeeding condition, where individuals could continue eating while keeping a lowrate ofconsuming, than it was in the condition where the increase in friquency offood provisioning compelled individuals to eat at intervals The animals' specificfeeding rhythm should, therefore, be an essential factor considered when seekingto improYe feeding conditions

In addition, the effectiveness of prolongation on feeding differed among thethree species Elephants spenr 8170 of the daylight hours feeding (M condition)Bears and chimpanzees spent only 14 atd Z4Vo, respectively (D condition) Forchimpanzees and bears, feeding time was sti below the levels observed in thewild In regard to feeding in the wild, the behavior can be divided into threesteps

I . Individuals initially forage for food Even when food is encountered. someof it may be covered with a hard shell or be hiding underground or behindrocks

2 Individuals, therefore, have to process food3 Individuals can proceed to ingest the food acquired through the two previ_

ous steps (consuming)

Feeding behavior in zoos includes the third step only consuming For ele-phants, continuing to feed might, in itself, be important Bears in the wild, how-ever, show a rhythm of feeding and exploring for food around their habitatAddressing and modifying the thee phases of feeding separately may be neces_sary to iDcrease their time of feeding It is not enough to increase the frequency offood provisioning, to create a rhythm of feeding, or both On the basis of these re_sults, we are carrying out experiments designed to encourage captive animals,time budgets offeeding behavior to approximate those ofthe wild, fiom the view-pointofthe specific characteristics of feeding and the thLree feeding phases: explor-ing, processing, and consuming

186 MoRIMURA AND uENo

ACKNOWLEDGMENTS

This study was supported by Sasagawa Scientific Research Grant 8-190 to

Naruki MorimuraWe thank the Maruyama Zoo staff for their kind help, and give sPecial thanks to

Mr Ken'ichi Kitamura, chief of the animal management section

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