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PRIMATES, 37(1): 79-86, January 1996 79 SHORT COMMUNICATION Anticipation of Conflict by Chimpanzees N. E KOYAMA and R. I. M. DUNBAR The University of Liverpool ABSTRACT. Captive chimpanzees appear to anticipate the occurrence of conflict during feeding by grooming and being in proximity at increased rates during the hour prior to feeding. The effect is more marked when food is clumped than when it is dispersed, suggesting that the proximate cause is the anticipation of increased levels of competition. Chimpanzees did not choose high ranking individuals more often as prefeed grooming partners; rather, they preferred to associate with their normal grooming partners (as reflected in post-feed grooming preferences) and close kin. A strong correlation between prefeed association patterns and spatial proximity during clumped feeding sessions suggests that their main concern is to be allowed to feed near individuals who are able to monopolize food sources. Key Words: Anticipation of conflict; Grooming; Chimpanzees; Tolerated theft. INTRODUCTION Primates appear to cultivate those relationships which can increase their fitness. Obser- vations of wild chimpanzees suggests that an individual is more likely to select another as a grooming partner if a close, supportive relationship already exists with it or if cultivating a stronger bond with a particular individual will be advantageous (GOODALL, 1986). There is now considerable evidence to suggest that nonhuman primates make use of plan- ning and foresight (for recent summaries, see SEYFARTH• CHENEY, 1988; BYRNE, 1995). Similarly, there is anecdotal (GOODALL, 1986) and experimental (TINKLEPAUGH, 1932; DOHL, 1968; RENSCH & Dt3HL, 1968) evidence to suggest that chimpanzees can anticipate the consequences of their own actions and those of third parties. The anticipation of a future event involves the ability to plan in the mind. Evidence for the anticipation of feeding time competition has been documented by DE WAAL (1987) in captive bonobos. Although grooming rates increased prior to feeding, the increase over baseline rates just failed to reach statistical significance. Nonetheless, DE WAAL suggested that the chimpanzees had learned when to expect food and so engaged in calming contact as feeding time approached. More convincing evidence for anticipation of future conflict has, however, been reported from other species. MAYAGOITIA et al. (1993) found that stumptail macaques (Macaca arctoides) anticipated forthcoming conflict during feeding by directing their affiliative behaviour during the prefeed period towards the most powerful group member -- the alpha male. They showed that the attractiveness of an individual (measured in terms of the competition to groom with that individual) depended on whether observations were made before or after feeding time.

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PRIMATES, 37(1): 79-86, January 1996 79

SHORT COMMUNICATION

Anticipation of Conflict by Chimpanzees

N. E KOYAMA and R. I. M. DUNBAR The University of Liverpool

ABSTRACT. Captive chimpanzees appear to anticipate the occurrence of conflict during feeding by grooming and being in proximity at increased rates during the hour prior to feeding. The effect is more marked when food is clumped than when it is dispersed, suggesting that the proximate cause is the anticipation of increased levels of competition. Chimpanzees did not choose high ranking individuals more often as prefeed grooming partners; rather, they preferred to associate with their normal grooming partners (as reflected in post-feed grooming preferences) and close kin. A strong correlation between prefeed association patterns and spatial proximity during clumped feeding sessions suggests that their main concern is to be allowed to feed near individuals who are able to monopolize food sources.

Key Words: Anticipation of conflict; Grooming; Chimpanzees; Tolerated theft.

INTRODUCTION

Primates appear to cultivate those relationships which can increase their fitness. Obser- vations of wild chimpanzees suggests that an individual is more likely to select another as a grooming partner if a close, supportive relationship already exists with it or if cultivating a stronger bond with a particular individual will be advantageous (GOODALL, 1986).

There is now considerable evidence to suggest that nonhuman primates make use of plan- ning and foresight (for recent summaries, see SEYFARTH • CHENEY, 1988; BYRNE, 1995). Similarly, there is anecdotal (GOODALL, 1986) and experimental (TINKLEPAUGH, 1932; DOHL, 1968; RENSCH & Dt3HL, 1968) evidence to suggest that chimpanzees can anticipate the consequences of their own actions and those of third parties.

The anticipation of a future event involves the ability to plan in the mind. Evidence for the anticipation of feeding time competition has been documented by DE WAAL (1987) in captive bonobos. Although grooming rates increased prior to feeding, the increase over baseline rates just failed to reach statistical significance. Nonetheless, DE WAAL suggested that the chimpanzees had learned when to expect food and so engaged in calming contact as feeding time approached.

More convincing evidence for anticipation of future conflict has, however, been reported from other species. MAYAGOITIA et al. (1993) found that stumptail macaques (Macaca arctoides) anticipated forthcoming conflict during feeding by directing their affiliative behaviour during the prefeed period towards the most powerful group member - - the alpha male. They showed that the attractiveness of an individual (measured in terms of the competition to groom with that individual) depended on whether observations were made before or after feeding time.

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80 N.F. KOYAMA & R. I. M. DUNBAR

One possible reason why DE WAAL'S results were not statistically significant is that he compared grooming levels in the 15 min prior to feeding with a baseline derived from all behaviour sampled prior to that time window. If chimpanzees have a long memory span, operate with a longer period of anticipation than 15 min or receive early cues that feeding is imminent, this will tend to obscure the differences between the baseline and prefeed periods.

In this paper, we attempt a more detailed test of this hypothesis by examining rates of proximity and grooming during the period before and after feeding in a captive group of chimpanzees. Because food was provided under both clumped and dispersed conditions, it was possible to determine whether the extent to which resources can be monopolized influences the animals' willingness to associate with each other.

If individuals do show evidence of anticipation of competition, their grooming patterns might reflect one of three proximate motivations. Low-ranking individuals might seek to buffer themselves against displacement by more dominant animals by forming or reinforc- ing coalitionary relationships in advance. Alternatively, animals might be seeking to create opportunities for tolerated theft by currying favour either with high-ranking individuals or with relatives so as to be able to feed on the same resource patches. These proximate processes will lead to different patterns of grooming during the prefeed period.

If alliances are used as buffers against attacks by more dominant individuals, then grooming with allies (and/or relatives) will be preferred to grooming with high-ranking animals and there will be evidence for the use of coalitions in feeding contexts; if grooming is used to curry favour with high-ranking animals so as to be able to gain access to food sources that they monopolize, then high-ranking individuals will be preferred over normal grooming partners; if grooming is used to curry favour with relatives/allies in order to feed near them, then grooming will be directed at these classes of individuals, but coalitions will not be much in evidence during feeding periods.

METHODS

SUBJECTS

The study group consisted of 11 Pan troglodytes (1 adult male, 4 adult females, 1 subadult male, and 5 juveniles/infants) at London Zoo. The group had been stable in com- position since a 6-yr-old male was removed from the group 18 months before the present study began. Excluding the dependent young, there were three pairs of related individuals: two of the adult females were sisters and the subadult male was the offspring of the adult male and one of the other females. The fourth female was the only individual with no kin relationships with any other group members; she was a rather asocial female who never mated with the male.

HOUSING CONDITIONS

The chimpanzees' accommodation consists of an outdoor and an indoor enclosure, both of which are furnished with ropes and climbing frames. There are ledges to sit on in both areas and the floors are scattered with straw which is removed daily when the indoor cage is cleaned out. The indoor enclosure is divided into a display pen area, visible to the public on one side through reinforced glass, with three rear sleeping dens which are not visible

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Anticipation of Conflict 81

to the public. The chimpanzee accommodation occupies a total area of 211m 2, of which 153m 2 is outdoors.

Food is placed in the outdoor enclosure before the chimpanzees are let outside in the morning (ca. 09:00); a second feed is then placed in the indoor enclosure before they are allowed to return to the indoor enclosure at midday (ca. 11:45); and a third feed is placed in the indoor area in mid-afternoon (ca. 15:15). The more constricted space of the indoor area compared to the outdoor compound meant that food was much more clumped during the midday and late afternoon feeding sessions. In contrast, the food was more widely dis- persed during the morning feeding session; as a result, individuals were less easily able to prevent others having access to food, either actively or passively.

All observations were made from outside the enclosures and the only times that the animals were not visible was if they briefly disappeared into the sleeping dens.

METHODS

A total of 51.3 hr of focal group sampling was carried out over a 3-month period. Scan samples were made at 5-min intervals for an hour prior to feeding (prefeed hour) and an hour after feeding had finished (postfeed hour). On each sample, the identities of all indi- viduals who were giving or receiving grooming and all those in spatial proximity (defined as two individuals sitting within arm's reach o f each other) were noted. (Note that the prox- imity measure includes individuals who were grooming as well as those that were simply sitting in contact.) In some cases, the timing of the morning feed made it impossible to collect a full hour's data for the prefeed period, thus resulting in unequal numbers of pre- and post-feed periods. Similarly, darkness during the winter sampling period meant that postfeed samples often had to be terminated early for the afternoon feeding sessions. There were 7 prefeed hours and 9 postfeed hours for the dispersed feeding times, and 15 prefeed and 12 postfeed hours for the clumped feeding times.

Additional observations were made during the actual feeding period. As no grooming occurred during this time, only the identities of those chimpanzees in close proximity to each other at 5-min intervals were noted.

Dominance relationships were determined from agonistic and submissive interactions recorded ad lib. The initiator of a displacement, chase, attack, or threat was considered to be dominant; the recipient of these interactions and initiator of any submissive acts (including presenting or the offering of an outstretched hand) was classed as the sub- ordinate individual.

MAYAGOITIA et al. (1993) measured the attractiveness of an individual by looking at the level of competition to groom that individual. However, competition to groom was not particularly evident in this group and so could not be used in this study.

RESULTS

ASSOCIATION FREQUENCIES

The mean frequency with which grooming pairs were recorded in each of the 5-min scan samples is given in Figure 1, with a three-point running mean used to smooth the data. Clumped and dispersed feeding sessions are graphed separately.

For all samples pooled, the mean prefeed grooming rate (mean number of grooming

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82 N.F. KOYAMA & R. I. M. DUNBAR

C:}05 4, , 13) ~ I .~ : ~ L I o E o4 , 0 ; �9 '

0 3 ~ ~ o el~ feed,

0 ' O , i i D i s p e r s e d f eeds

" o 2 ' " - , ' ,t:

( -0 .1 �9 ~ ! �9 i . ~ , ~ ~ . i

-60 -45 -30 -15 0 10 25 40 55 Time from Feeding (mins)

Fig. l. Mean number of dyads who were recorded as grooming on scan samples taken at 5-min intervals during the hour before and after feeding (indicated by the vertical lines at time 0) during clumped and dispersed feeding sessions. The plotted values are three-point running means. Sample sizes are 7 prefeeding hours and 9 postfeeding hours for dispersed sessions and 15 prefeeding and 12 postfeeding hours for clumped sessions.

dyads per scan=0.34) is nearly three times that observed during the postfeed period (0.12 dyads per scan). Grooming rates were clearly significantly higher during the prefeed period (Mann-Whitney test, n~ = n2 = 13, 5-min scan sample means, p < 0.05).

The possibility that diurnal cycles in activity were a confounding factor can be excluded by comparing prefeed and postfeed samples that occurred at the same time of day. Prefeed grooming rates were higher than postfeed rates in 22 out of 30 matched pairs (X2=6.533, df= 1, p < 0.02). This suggests that time of day was not exerting a significant effect.

The first 15 min prefeed and the last 15 min postfeed can be considered as baseline values that are unlikely to be affected by the feeding sessions either side of them. We therefore pooled the data for these two periods from each block and compared the mean values against the 15 min prior to feeding (prefeed) and the 15 rain immediately after feeding ended (postfeed). A Kruskal-Wallis non-parametric ANOVA indicates that there are signifi- cant differences between the blocks (KW=7.778 corrected for ties, df=2, p< 0.001). Post hoc tests for all possible pairwise comparisons revealed only two significant comparisons at the p=0.05 level: baseline vs prefeed and prefeed vs postfeed.

During dispersed feeding periods, 5/7 dyads groomed more before feeding than after (binomial test: ,o=0.227, one-tailed), with 8 dyads in which no grooming was recorded. During clumped feeding periods, 13/13 dyads groomed more before feeding than they did afterwards, with just 2 dyads that never groomed (binomial test: p < 0.001). The proportion of all grooming within a dyad that occurred during the prefeed hour was not significantly higher during clumped (midday and afternoon) feeding sessions than during dispersed (morning) sessions (Wilcoxon test: N = 7 dyads for which there are data from both sessions, p > 0.05), but this may have reflected the smaller size of the dispersed sample.

Figure 2 gives the mean frequency with which dyads were recorded in proximity during the scan samples. As with grooming, spatial proximity increases as feeding time approaches, reaching a plateau as early as 35 - 40 min before feeding is due. During the feeding period, the rate of association rises steeply, then falls to a relatively low level during the postfeed

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Anticipation of Conflict 83

1.2

o 13. 0 .8 .=_

~ 0.6 Q d 0.4 z

r

0.2

. . . .

r t \

, '! ,,'

r s f

.Q

@-d, , I

i Cl<umped feeds

Dispersed feeds

- 6 0 - 4 5 - 3 0 - 1 5 0 10 25 40 55 Time from Feeding (mins)

Fig. 2. Mean number of dyads recorded as being in proximity on scan samples taken at 5-min intervals during the hour before and after feeding (indicated by the vertical lines at 0). The plotted values are three-point running means. Sample sizes as for Figure 1.

�9 ~ 2.2

s 2

13.. 1.8 i - ~ 1.6

~ 1.2

6 1 Z e- 0.8

~ 0.6

�9

f J/z// /.�84 �9

fJ o

o .z" .

0 10 20 30 40 Time Since Start of Feeding (mins)

ciom.o ,oo i I Dispersed food

Fig. 3. Mean number of dyads recorded as being in proximity on scan samples taken at 5-min intervals during the feeding period when food was clumped (filled symbols: N=I5 sessions) or dispersed (open symbols: N= 9 sessions).

period. Only 2/12 dyads (with 3 additional ties) spent more time in association before feeding than afterwards during dispersed periods (binomial test: p=0.613), but 11/14 (with 1 additional tie) did so during clumped feeding periods (p = 0.029). Dyads were more likely to be associated before feeding in clumped periods than during dispersed sessions (Wilcoxon test: N = 9 dyads for which there are data from both sessions, p < 0.05).

Figure 3 shows that animals tended to come into increased proximity as the feeding session proceeded more often when food was clumped than they did when food was dis- persed [Spearman correlations: rs=0.15 for dispersed food, N = 5 , ns, rs=0.85 for clumped, N = 9 , p<0 .02 ; t (0.85=0.15)=3.013, df=7, p<0 . 02 , two-tailed]. Competit ion for access to food is thus likely to be higher during clumped feeding sessions than during dispersed feeding sessions.

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84 N.F. KOYAMA & R. I. M. DUNBAR

DOMINANCE RANK, GROOMING, AND PROXIMITY RATES

A dominance matrix was constructed for the six adult and subadult members of the group using the 33 agonistic interactions recorded during ad lib sampling. The hierarchy (given in Table 2) was strictly linear with no wins-against-the-hierarchy.

There was no significant relationship between dominance rank and the increase in grooming either given or received in the prefeed hour for any of the six animals in either the dispersed feeding condition (Spearman correlations for individual subjects: -0 .08< rs<0.55 for grooming given and -0.80<rs<0.70 for grooming received, N=5, p>0.05 in each case) or the clumped condition (Spearman correlations: -0.50 < rs < 0.60 for groom- ing given; -0.70 < rs < 0.68 for grooming received, N= 5, p > 0.05). (Combining one-tailed p-values using Fisher's procedure to test for consistency of underlying trends yields X2= 18.33 and X2= 13.30 for grooming given and received, respectively, df= 12, p>0.20 in each case, for the dispersed condition, and X2= 10.32 and X2= 14.55 respectively, df= 12, p > 0.20, for the clumped condition.) Similarly, with one exception, there was no evidence to suggest the increase in the level of proximity in the prefeed hour correlated with the rank of the target animal (Spearman correlations: - 0.08 < rs < 0.98, p > 0.05 except in the last case, for the dispersed food condition, X2=7.99, df=12, p>0.70; -0.10<rs<0.50, p>0.05, for the clumped condition, X2=12.81, df=12, p>0.30; N=5 in all cases).

Fights were more likely to occur during clumped feeding sessions than during dispersed ones (Table 1: Fisher exact test, p= 0.05), indicating increased levels of aggression/tension when food was less widely distributed. Despite this, no coalitions were observed during either type of feeding session.

Table 1. Occurrence of fighting during feeding periods.

Number of feeding sessions with

Condition Fights No fights Total

Dispersed 0 9 9 Clumped 5 8 13

Total 5 17 22

KINSHIP, GROOMING, AND PROXIMITY RATES

There are three pairs of relatives in the group: Mandy and Barbie were sisters, Fanny and Bobby were mother and son, and Johnny and Bobby were father and son. When deter- mining the influence of kinship on the distribution of grooming and proximity in the prefeed hour, Johnny and Bobby were excluded from the analysis because they only ever groomed each other once. Bobby's relationship with his mother was far stronger and so took up the greatest proportion of his social time.

We calculated the absolute difference between prefeed and postfeed grooming frequen- cies with kin and non-kin for each of the four animals that had a close relative in the group. Kin were groomed at much higher rates (relative to the post-feed condition) during the pre-feed session (Mann-Whitney test, z= - 3.924, p < 0.001; comparing each indivi- dual's value with its kin against the mean for its values with non-kin gives 4/4 cases with kin greater: binomial test, p=0.06). This suggests a preference for relationships formed with kin in these conditions rather than with high-ranking animals per se.

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Anticipation of Conflict 85

Table 2. Spearman correlation coefficients for the relationship between prefeed proximity or groom- ing frequency and feeding time proximity partners.

Correlation between proximity during feeding and Prefeed proximity score Prefeed grooming frequency* Dispersed Clumped Dispersed Clumped Dominance rank

Johnny - 0.832 0.225 - 0.444 0.564 1 Koko 0.725 0.375 1.000 0.344 2 Fanny - 0.671 0.45 - 0.287 0.447 3 Barbie 0.325 0.7 - 0.344 0.900 4 Mandy 0.583 0.825 0.968 1.000 5 Bobby - 0.613 1.0 - 0.395 0.791 6

*Grooming during second 30-min session prefeed.

The proximity partners during the prefeed hour and the feeding period were analyzed to determine whether or not the relationships being serviced and strengthened in the prefeed hour were the same as those which were being called upon in the feeding period. The proximity data were analyzed separately for the dispersed and the clumped feeding times and the rs values for each individual are given in Table 2. For five of the six chim- panzees, proximity partners during the prefeed and feeding period correlated more closely during the clumped feeding condition than they did when food was dispersed. Similarly, grooming frequencies were significantly more highly correlated with feeding proximity partner scores in clumped than during dispersed sessions (Table 2: Mann-Whitney test, nl = n2 = 6, p = 0.006). During the prefeeding period, the animals spent more time near, and groomed more frequently with, those animals they ended up being near to during feeding.

The absolute values of the correlation coefficients correlate with the dominance hier- archy during clumped feeding sessions (proximity scores, rs=l.O0, p=0.005; grooming scores, rs=0.657, p=0.20, two-tailed; N = 6 in both cases), but not during dispersed feeding sessions (proximity scores, rs=0.26; grooming scores, rs=0.029; N =6 , p>0.50 , two-tailed in both cases). This suggests that the tendency to maintain close proximity to your prefeed ally in the feeding period declines as the individual's rank increases. This suggests that access to food clumps is not a problem for the high-ranking individuals, so that maintaining prefeed proximity to established allies is not necessary. Once again, the fact that this relationship holds only during clumped feeding sessions suggests that these requirements are less pressing when animals are less able to prevent low-ranking animals from gaining access to food.

DISCUSSION

The findings of this study support the hypothesis that chimpanzees are able to anticipate future conflict and plan their behaviour accordingly. The fact that the chimpanzees did not groom all group members equally during the prefeed session suggests that they were not simply trying to reduce general levels of tension within the group or to calm their own sense of excitement at the prospect of feeding. The latter conclusion is reinforced by the fact that grooming and proximity rates only increased in the prefeed hour before lunchtime and afternoon feeding times (when the food would be clumped indoors) and not in the prefeed hour before morning feeding sessions (when the food would be dispersed around the outside enclosure). This distinction would not be expected had the increase in social activity merely been due to the excitement of anticipated feeding.

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86 N. E KOYAMA & R. I. M. DUNBAR

An alternative explanation for the differences in grooming rates might be that the change in behaviour was simply a consequence of the different housing conditions (e.g. cramped into an indoor enclosure before the morning feed and free to disperse in the larger outdoor enclosure after it). However, if this were so, we would expect the reverse to be true for the midday and afternoon feeds when dispersal outside was followed by spatial concentration indoors, but the pattern is in fact the same as that observed for the morning feeds.

No relationship was found between rank and the increase in grooming and proximity rates. Individuals did not appear to compete to groom high-ranking group members in the prefeed hour. It seems that, in this group at least, kin bonds were more important than the dominance rank of group members. This makes the suggestion that animals are trying to curry favour with high-ranking animals in order to be able to feed near them unlikely. The fact that coalitions are rarely (if ever) observed during feeding makes it unlikely that the animals are trying to bolster existing coalitions in order to buffer themselves against harassment by higher-ranking animals during feeding. Instead, there was strong support for the suggestion that animals groom (and sit with) their main grooming partners (and/or relatives) in order to be able to feed near them when compression of the feeding site makes feeding squabbles likely. In effect, the animals seem to be trying to create an opportunity for tolerated theft to take place.

Acknowledgments. We thank Dr. JoB GIPP and the Zoological Society of London for permission to carry out the study, and the primate house keepers for help with identifying the animals and information on their backgrounds. We are particularly grateful to two anonymous referees for their comments.

REFERENCES

BYRNE, R. W., 1995. The Thinking Primate. Oxford Univ. Press, Oxford. DOHL, J., 1968. Ober die fiihigkeit einer schimpansin, umwege mit selbstiindigen zwischenzielen zu

iiberblicken. Z. TierspsychoL, 25: 89-103. GOODALL, J., 1986. The Chimpanzees of Gombe. Harvard Univ. Press, Cambridge, Massachusetts. HARCOURT, A. H., 1987. Dominance and fertility among female primates. J. Zool. London, 213:

471 - 487. MAYAGOITIA, L., A. M. SANTILLAN-DOHERTY, L. LOPEZ-VERGARA, (~ R. MONDRAGON-CABALLOS, 1993.

Affiliation tactics prior to a period of competition in captive groups of stumptail macaques. Ethol. Ecol. EvoL, 5 (4): 435- 446.

RENSCH, B. • J. DONE, 1968. Wahlen zwischen zwei iiberschaubaren labyrinthwegen durch einen schimpansen. Z. Tierspsychol., 25: 216-231.

SEYFARTH, R. M. & O. L. CHENEY, 1988. Do monkeys understand their relations? In: Machiavellian Intelligence, R. W. BYRNE & A. WH1TTEN (eds.), Clarendon Press, Oxford, pp. 69-84.

TINKLEPAUGH, O. L., 1932. Multiple delayed reaction with chimpanzees and monkeys. J. Comp. Psychol., 13:207 - 243.

DE WAAL, F., 1987. Tension regulation and non-reproductive functions of sex in captive bonobos (Pan paniscus). Nat. Geograph. Res., 3:318 - 335.

WHITTEN, P. L., 1983. Diet and dominance among female vervet monkeys (Cercopithecus aethiops). Amer. J. PrimatoL, 5: 139-159.

- - Received: May 30, 1994; Accepted: August 17, 1995

Authors' Names and Address: N. E KOVAMA and R. I. M. DUNBAR, Department of Psychology, The University of Liverpool, P.. O. Box 147, Liverpool L69 3BX, England.