Use of novel objects to enhance environments of captive chimpanzees

ZOO Biology 7~15-23 (1988)

Use of Novel Objects to Enhance Environments of Captive Chimpanzees Daniel Paquette and Jacques Prescott

Jardin Zoologique du Quebec, Quebec, Canada

A small group of chimpanzees was allowed to manipulate different quantities of novel objects in order to enhance their captive conditions. This procedure led to a general increase in the manipulation frequency by the apes. It decreased their inactivity and their self-grooming, and almost eliminated the abnormal behaviors displayed by one individual. The distribution of novel objects did not affect the total frequency of social interactions and did not increase the aggressivity of the animals, even though dominant individuals secured most of the objects when only a small number of them were available. Following their familiarization with the novel objects, the chimpanzees’ manipulation frequency decreased whereas self- grooming and abnormal behaviors were increased. Suggestions are made on how to maximize the use of a limited bank of toys to occupy captive chimpanzees.

Key words: chimpanzee, manipulation, exploration, habituation, dominance, captivity,

INTRODUCTION

management

Captive chimpanzees are often subject to boredom or lack of occupation. Lack of stimulation from a nonvariable or restrictive enclosure generally leads to inactivity and abnormal behaviors in primates [see Morris, 1964; Erwin and Deni, 1979; Maple, 1979, 1980; Maple and Hoff, 1982; Clarke et al., 19821. Chimpanzees are curious and highly manipulative [Kohler, 1927; Goodall, 1965; McGrew, 19771, and many zoos provide them with objects to enhance their activity [Maple, 19791. Wilson [ 19821 recently showed that the presence of stationary, movable, and temporary objects was strongly correlated with the level of activity in captive apes.

Novelty being the most important factor in eliciting exploration in animals Putler, 1965; Hutt, 1967a; Welker, 19711, it has been suggested that substituting novel objects periodically would be advisable [Maple, 19791.

The purpose of this study was to measure the effects of presenting novel objects on the behavior of a group of captive chimpanzees and to determine the number of

Received for publication July 31, 1986; accepted October 12, 1987.

Address reprint requests to Jacques Prescott, Jardin zoologique du Qutbec, 8191 Avenue du Zoo, Charlesbourg, QuCbec, Canada GIG 4G4

0 1988 Alan R. Liss, Inc.

16 Paquette and Prescott

objects to be provided to the animals and the period of time before complete habituation.

METHODS Subjects

Four chimpanzees (Pan troglodytes schweiizfurtii) born in captivity and raised by human surrogate mothers were the subjects of this experiment. One pair (Spock u and Sophie Q) was 8 years old and the other pair (Maya Q and Merlin u) was 7 years oId at the beginning of the experiment.

Housing The chimpanzees were housed in an indoor exhibit open for public viewing at

the Jardin Zoologique du Qukbec. The playroom was essentially square in shape with an 8 x 8 meter floor surface and a height of 5.8 m. The room was furnished with climbing structures, shelves, two rubber balls, swings, and hanging tires. Animals could be observed from a one-way mirror window.

The subjects were put together in the playroom daily from 7:30 AM to 3:30 PM. Each pair spent the rest of the day and night in a smaller adjacent pen (floor 2.8 X

2.8 m, height 2.5 m).

Procedure The animals were exposed to five experimental conditions during which they

were presented with either 0, 1, 3, 6, or 10 novel objects. The objects were rubber or plastic toys for small children that were selected for durability. They were all different but had approximately the same size, color, and comparable “configural complexi- ties,” defined by McCall [I9741 as the number of nonredundant elements in a form. In each experimental condition (except 0 toys), one of the toys could produce a sound when squeezed. It must also be stressed that the plastic or rubber toys constituted a relative novelty to the animals that had in past years the opportunity to manipulate other similar objects. The O-novel-object condition was the baseline situation where the chimpanzees could play with two rubber balls and a tire. The order of conditions was random: the O-object condition was followed by the 3-object condition, then 6-, lo-, and l-object conditions.

For each condition, the objects were placed in the playroom prior to the chimpanzees’ arrival. Observations began two hours after the animals were introduced into the room and lasted for two hours. This procedure was adopted in order to avoid the burst of activity and excitation normally displayed by the apes following their introduction into the playroom, where they are given their first meal of the day.

The apes had access to the novel objects only during the 8-hour period spent in the playroom. The behavior of each individual was instantaneously recorded each minute of the observation period (scan sampling) and classified according to the following categories: inactivity (resting or staying immobile), manipulation of objects, self-grooming, social interaction, locomotion, abnormal behavior (coprophagy, licking of the walls, urine drinking), and others. Social interactions comprised social grooming, watching a peer (looking intently at a peer at less than an arm’s-length), social play (with play-face), threats and aggressions, and other affiliative interactions.

Occupation for Captive Chimpanzees 17

For each condition, the animals were observed for consecutive days until the mean manipulation frequency of the group was equal to or less than 15% of the total observation time. The 0-novel-object condition served as a baseline, determined after three consecutive observation periods (6 hours of observation). Each condition was only presented once and an interval of 3 days was allowed between each condition.

Comparisons between the conditions were performed by compiling the percentage of time devoted to each activity by each chimpanzee during the first three days of observation (6 hours). The Kolmogorov-Smirnov test was used to compare each experimental condition with the baseline condition [Lehner, 19791.

Interindividual dominance ranks were determined from the observed rate of supplantings and displays as defined by Simpson [ 19731.

RESULTS

Effect of the Number of Novel Objects

Novel objects had a positive effect on the percentage of time devoted to manipulation by each chimpanzee, as calculated over the first three days of each condition (Fig. 1). Manipulation increased for the entire group from 8% of the time in the baseline condition of 0 novel objects to 54% of the time with 10 novel objects.

MANIPULATION INACTIVITY

4 ABNORMAL BEHAVIORS SELF-GROOMING 6 0

Z

U 40

20

!-

u

e u

LOCOMOTION SOCIAL INTERACTIONS

20

0 1 dJIdL-LL-L 2:1 JLdAWllll 0 1 3 6 1 0 0 1 3 6 1 0

NUMBER OF NOVEL OBJECTS

Fig. 1. Percentage of time devoted by each chimpanzee to each behavioral category, calculated over the first 3 days of observation within each experimental condition.


A significant increase in manipulation (Kolmogorov-Smirnov test, P < 0.05) was found when at least one object was introduced in the playroom.

In the baseline condition, the chimpanzees were inactive 37% of the time. The inactivity frequency of Sophie, Maya, and Merlin decreased to 10% in the 10-novel- objects condition. Spock was most active (only 16% inactivity) when only one novel object was available. The only significant difference in the activity levels of the apes was found between the 0-novel-object and 10-novel-object conditions (Kolmogorov- Smirnov test, P < 0.05).

Self-grooming had its lowest value with 10 novel objects for Sophie and Maya, 6 and 10 objects for Merlin, and 3 objects for Spock. Overall, the frequency of self- grooming was reduced from 30% (baseline condition) to 14% with 10 objects, and this decrease was significant with 3, 6, and 10 objects compared to the baseline condition (Kolmogorov-Smirnov test, P < 0.05).

In the baseline condition, Sophie showed a 25 % frequency of abnormal behavior (mainly licking and coprophagy). These behaviors decreased markedly as soon as at least one novel object was available. It is interesting to note that locomotion and the number of social interactions were not significantly affected by the availability of novel objects (Fig. 1).

Most interactions among the group members were affiliative rather than aggressive (Table 1). The relative frequency of social grooming generally decreased as the number of objects increased. But the correlation between the absolute frequency of social grooming and the number of available objects was not significant (r = 0.76, P > 0.05). The chimpanzees spent more time watching a peer when only 3 objects were available.

The presence of novel objects increased the number of social interactions occurring over an object, but these never represented more than 25% of all observed interactions (Table 2).

TABLE 1. Percentage of time devoted to social activities during the first three days of each experimental condition

Number of Novel Obiects Social Interactions 0 1 3 6 10

Social grooming 69 60 44 54 33 Watching a peer 14 14 35 24 12 Social play with 9 0 13 9 13

Other affiliative 8 22 8 10 31

Threats and 0 4 0 3 11

play-face

interactions

aggressions

TABLE 2. Percentage of social interactions occurring over an object in each experimental condition

Condition 0 1 3 6 10

Social 0.8 4.9 25.4 23.9 17 interactions


Q, 0 0 C a)

+

U

r] 20

0

D 0

/ 0

S o p h i e

M a y a Merl in

S D o c k

1 3 6 10

Number of novel objects

Fig. 2. Percentage of manipulation by each individual as a function of the number of novel objects.

Dominance Effects The apes were obviously interested in the novel objects. However, no aggres-

sion or fighting for the apparent purpose of securing these objects was observed, even when the objects were less numerous than the animals. When only one novel object was available, the manipulation frequency of each individual corresponded to its hierarchial dominance rank. Spock, the most dominant subject, displayed the most manipulative behavior, followed by Sophie, Merlin, and Maya (Fig. 2). A Chi-square test applied to absolute frequencies indicated a significant difference between subjects (P < 0.01).

As the number of novel objects was increased, this tendency was somewhat modified to show the real propensity of each individual to manipulate when objects were available to all of them. With 10 objects, Spock’s manipulation frequency was the lowest, indicating that he was less interested than the others in this type of activity (Fig. 2 ) . In this condition, he and Sophie tended, however, to secure more objects at the same time than their subordinates during manipulation (Table 3).

TABLE 3. Distribution of the manipulation frequency of each chimpanzee in relation to the number of objects secured

Number of objects Spock Sophie Merlin Maya secured (N= 147)a (N=270) (N=174) (N = 193)

1 63.3% 73.3% 70.7 % 90.2% 2 0 11.9 18.4 4.7 3 0 0.4 2.9 1.0 4 0.6 0.4 3.4 4.1 5 0 0.7 4.0 0 6 8.2 8.5 0.6 0 7 21.1 3 .O 0 0 8 6.8 1.5 0 0 9 0 0.3 0 0

10 0 0 0 0

a(N = number of point samples where manipulation was observed in the 10-novel-object condition)


One could argue that the animals could manipulate only when some objects had not been currently secured by the others. The percentage of time during which there was no object available to a given individual for a given condition was calculated. This was performed for each subject using the following equation (which exemplifies Maya’s value):

(Sp Ai + So Bi + Me Ci) PN

x 100 = %Ma cp, , where

P = total number of point samples (in this case 360) N = total number of novel objects available in the playroom

Sp, So, Me = number of point samples recording manipulation of objects by Spock, Sophie, or Merlin

A, B, C = number of objects secured by Spock, Sophie, and Merlin during each point sample %Ma = percentage of nonavailability of objects for Maya

According to this equation, the percentage of nonavailability of objects decreased for each individual as the number of objects presented to the animals was increased. With six objects or more, the four animals had an almost equal opportunity to manipulate (Fig. 3).

Effect of Time Over the days, the chimpanzees’ manipulation of objects gradually decreased

(Fig. 4). It took 3, 5 , 4 , and 7 days to reach the 15% manipulation frequency for the 1-, 3-, 6-, and 10-object conditions, respectively.

A simple regression analysis based on least-squares estimates indicated that this decrease in manipulation was not statistically significant for 1 object (r = 0.747, P

\ Merl in & M a y a 4 0

20- 0 1 3 6 10

Number of novel objects

Fig. 3. Percentage of nonavailability of the objects for each chimpanzee in relation to the number of novel objects.


g 100 KJ In + .- C 80 0 n.

w- 0 L. 0,

-D

3 C

E

C 0

2

A CONDITION 1 8 CONDITION 3 * CONDITION 6

CONDITION 10

20

8 1 I I I I I I 1 2 3 4 5 6 7

Time (days)

Fig. 4. Daily manipulation frequency of the chimpanzees within each experimental condition.

> 0.05), but was significantly linear for 3 (r = 0.936, P < 0.01), 6 (r = 0.995, P C 0.01), and 10 objects (r = 0.931, P < 0.005). In this latter condition, for example, the mean manipulation frequency of the group decreased from 51 % to 10% in only 7 days.

The 10-object condition was the only condition offering a sufficient number of data points to allow a statistical analysis of the effect of time on the other behavioral categories. The Wilcoxon test applied to data collected during the first three and last three days of the 10-object condition showed a significant increase of self-grooming and abnormal behaviors and a significant decrease in the manipulation frequency (P < 0.05). During the same period, inactivity remained low and constant.

DISCUSSION

The presentation of novel objects specifically affected the behavior of captive chimpanzees. It increased their manipulation frequency and simultaneously decreased their inactivity. The animals also devoted less time to self-grooming, and one individual almost ceased his abnormal activities. Social interactions were not affected, with the exception of a slight decrease in social grooming, and not one aggressive interaction could be related to this procedure. The distribution of objects was thus confirmed as an effective way to occupy captive chimpanzees.

The results of this procedure were generally similar to those obtained by Clarke et al. [1982] after translocating a small chimpanzee group from a laboratory environment to a naturalistic man-made island: decrease in self-grooming and stereotyped behaviors, and nonsignificant variation in the total frequency of social interactions.

We also found that the effects on the behavior were more pronounced when the number of available objects exceeded the number of animals. Dominant individuals


tended to secure most of the objects and to a certain extent prevented the subordinates from manipulating them. But a larger number of objects increased the possibilities of lower-ranked individuals to manipulate them.

It is well known that repetitive or continual exposure of a subject to a given stimulus generally leads to habituation [Hutt, 1967b; Ratner, 19701. The decrease in the manipulation rates of the chimpanzees over the days of the experiment can be explained by this process. According to Welker [1961, 19711, familiarization could even be viewed as a direct consequence of habituation.

The decrease in the response of animals to novelty is generally related to the complexity of the stimulus [Hutt, 1967bl; the habituation to a weak stimulus being faster than to a stronger one. In this respect, Welker [1956; in McCall, 19741 showed that chimpanzees 3-4 and 7-8 years old manipulated more when the objects were movable, large, bright, configurally heterogeneous, and capable of producing audi- tory or visual changes. This could explain why longer habituation periods were obtained with the larger number of objects (i.e., conditions offering the greatest diversity of stimuli).

The novelty of an object is related to the age [Loizos, 19671 and experience of the animals [Baldwin and Baldwin, 19771. On one hand, young animals will be more interested in a novel object than older subjects, with the habituation being faster in the latter [Schaffer and Parry, 19691. On the other hand, animals raised in an enriched environment will be less attracted by novel stimuli than those raised in monotonous conditions, except if they have been kept from novelty for a long time. In this study, the four chimpanzees were raised in a situation where for many years they regularly played with new objects but had not had the opportunity to do so for one year prior to the experiment. Their previous contacts with children’s toys and their previous knowledge of these kinds of objects could explain why, even with 10 available objects, their manipulation frequency decreased to 15 % in less than 7 days.

These considerations imply that the distribution of 10 novel objects, for example, to a group of chimpanzees would lead to a reduction of the manipulation level by the animals over time. It has been held that a continuous response wanes faster than a transitory response [Hinde, 19661 and that habituation occurs more rapidly with the reduction of time intervals between stimuli. There are indications that one could extend the habituation period of the chimpanzees and maximize the use of a limited bank of objects in two ways: by reducing the daily exposure period or by increasing the time intervals between the presentation of objects.

CONCLUSIONS

The following conclusions were drawn from this study: 1. The distribution of novel objects increased the manipulation frequency and

2. This procedure did not affect the total frequency of social interactions and did

3. The tendency of dominant individuals to secure most of the objects was counter-

4. The chimpanzees’ manipulation of objects gradually decreased over time, sug-

decreased the inactivity and self-grooming of captive chimpanzees.

not increase the aggressivity of the animals.

acted by increasing the number of available objects.

gesting the importance of a periodical substitution of the objects.


ACKNOWLEDGMENTS

We are very grateful to William L. Vickery and Bernard Chapais for their helpful comments on the manuscript. This work was made possible thanks to financial support from the Fonds FCAR de la Province du Qukbec and to the collaboration of the authorities of the Jardin Zoologique du Quibec and the Ministbre du Loisir, de la Chasse et de la Pgche.

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Use of novel objects to enhance environments of captive chimpanzees