conflict and post-conflict behavior in a small group of chimpanzees 13

PRIMATES, 43(3): 223-235, July 2002 223

Conflict and Post-conflict Behavior in a Small Group of Chimpanzees

AGUST1N FUENTES, Notre Dame UniversiO'

NICHOLAS MALONE, University of Oregon

CRICKEqq'E SANZ, Washington University

MEGAN MATHESON, Central Washington UniversiO:

and LORIEN VAUGHAN, San Diego Wild Anhnal Park

ABSTRACT. Chimpanzee research plays a central role in the discussions of conflict negotiation. Reconciliation, or the attraction and affiliation of former opponents following conflict, has been proposed as a central element of conflict negotiation in chimpanzees and various other taxa. In an attempt to expand the database of chimpanzee conflict resolution, conflict and post-conflict behavior were recorded for a small group of socially housed chimpanzees at the Chimpanzee and Human Communication Institute, at Central Washington University, Data were collected over six 6-week periods between 1997 and 2000, for a total of 840 hours of observation, resulting in a substantial post-conflict (PC) and matched control (MC) data set. The data demonstrate this group's tendencies to maintain visual contact and closer proximity after conflicts. Dyadic corrected conciliatory tendencies ranged between 0 - 37.5% and averaged 17.25% across all dyads. Individual corrected conciliatory tendencies ranged between 5.8 and 32%. The results of this study combined with recent publications on captive and free-ranging chimpanzee post-conflict behavior suggest that variation in post-conflict behavior may be important to our understanding of chimpanzee conflict negotiation, and may also have implications for the design and management of captive chimpanzee enclosures and social groups, respectively.

Key Words: Conflict; Post-conflict behavior; Chimpanzee; Pan troglodytes; Reconciliation.

INTRODUCTION

Primatologists, Anthropologists, and Psychologists have long been interested in aggressive behavior in nonhuman primates. A large body of research has revealed a wide continuum of conflict across all age/sex classes and the integral role it holds in the daily lives of highly social group-living organisms (DE WAGE, 1993, 2000; MASON • MENDOZA, 1993). Our current view characterizes social conflict as a component of subtle and complex social relationships, and important to the dynamic processes involved in their formation and maintenance (AURELI t~ DE WAGE, 2000; DE WAAL, 2000).

The current definition of reconciliation operationally defines attracted, dispersed, and neutral pairs (DE WAAL& YOSHIHARA, 1983). DE WAAL and YOSH|HARA suggested that following conflict, attraction rather than dispersal is likely to occur and former opponents are likely to interact affiliatively through close proximity and body contact. VEENEMA et al. (1994) refined the PC (post-conflict)-MC (matched control) data collection methodology with the addition of a correction factor that removed baseline behavior from post-conflict interaction data (see also VEENEMA, 2000). This resulted in a more robust measure called the Corrected Conciliatory Tendency (CCT) (attracted-dispersed pairs/total number of conflict pairs).

To date, a number of post-conflict studies have been undertaken across primate taxa (reviewed by KAPPEEER & VAN SCHAIK, 1992; DE WAAL, 1989, 1993; AUREL! & DE WAGE, 2000). In general the results have demonstrated a range in post-conflict responses, particularly

224 A. FUENTES et al.

in rates and styles of reconciliation (see KAPPELER & VAN SCHAIK, 1992; DE WAAL, 1993; AURELI & DE WAAL, 2000 for overviews of the data sets). Other post-conflict behavior patterns investigated include consolation (affiliative interaction with third party after a conflict) and redirection (aggression directed towards other group members) (see AURELI & DE WAAL, 2000). One of the major findings emerging from the growing number of post-conflict behavior studies is that of variability in conflict negotiation and resolution (see AURELI & DE WAAL, 2000; CASTLES et al., 1996; CORDS & KILLEN, 1998; SCHINO et al., 1998).

Although there are a number of hypotheses for why primates tend to reconcile (or not reconcile) after conflict have arisen, two have received the most attention. The two primary models for conflict resolution are the valuable relationship hypothesis (CORDS & AURELI, 1996) and the uncertainty reduction hypothesis (SILK, 1996). Both of these models find some support from existing data, although differing interpretations of the data leave many vagaries yet to be settled (AURELI & SMUCNY, 1998; CORDS ~, AURELI, 1996, 2000; SILK, 1996, 1998, 2000). It is important to note that while the former hypothesis speaks to long-term relations within the group and the latter emphasizes immediate, or "current" behavior, the two are not necessarily exclusive. Proponents of both models stress the need for continued and expanded data collection across primates and other taxa to address these issues. Also, there is a clear need for a larger body of quantitative data with which to assess these and other models for the behavior of organisms after conflict.

The purpose of this study is to add to the existing body of literature examining post-conflict behavior, including reconciliation, in captive chimpanzees (ARNOLD & WHITEN, 2001; DE WAAL, 1987, 1989, 1993; DE WAAL • AURELI, 1996; DE WAAL t~ VAN ROOSMALEN, 1979; PREUSCHOFI" et al., 2002). The five chimpanzees of the Chimpanzee and Human Communication Institute (CHCI) are a small group, all adults, where we have long-term knowl- edge of personal histories and behavioral records combined with excellent observational conditions. While four of the five chimpanzees in this group were cross-fostered all have been in exclusive chimpanzee groups for the last 19 years. This group's behavioral repertoire has some elements not common in other captive chimpanzee colonies, however their overall behavioral profiles are well within general chimpanzee parameters (JENSVOLD et al., 2001; MARTIN et al., 1999).

Here we report the first four years' data of a long-term project to examine the conflict and post-conflict behavior in this small group of chimpanzees.

METHODS

SUBJECTS

See Table 1 for biographical information on this group of five adult chimpanzees (Pan troglodytes). These chimpanzees have been housed together since 1981. They have resided in their present enclosure at the CHCI since 1993. Four of the chimpanzees were cross-fostered and acquired American Sign Language (ASL) from their human caregivers (GARDNER et al., 1989). The fifth (Loulis) acquired his signs from his adopted mother Washoe and the other chimpanzees (FOuTS et al., 1989).

The chimpanzees' facility consists of an outdoor enclosure, two indoor exercise rooms, and a night enclosure. The enclosure encompasses 1909 m 2 and offers 4417 m 2 of functional surface area. The enclosures are furnished with a variety of structural enrichment items. The chimpanzees are provided three meals a day in the night enclosure. Each day caretakers provided social and object enrichment to the chimpanzees (FOUTS et al., 1989, 1994).

Conflict and Post-conflict Behavior

Table 1. Participant biographical information.

225

Participant Age in years as of 2001 Sex

Washoe Approximately 36 Female Moja 30 Female Tatu 27 Female Dar 26 Male Loulis 23 Male

PROCEDURE

Data were collected for a total of 840 hours over six 6-week periods [June - August 1997, June - August 1998, January - February 1999 (1999a), June - August 1999 (1999b), January - February 2000 (2000a), and June - August 2000 (2000b)]. Data were collected from 09:00 to 11:00 and 13:00 to 15:00 each weekday. Data were also collected from 12:00 to 13:00 five days a week in 1997 and three days a week in 1998, 1999, and 2000. Data were collected via focal follows by two observers during each collection session so that both participants in a conflict could be accurately recorded.

Data collectors recorded: conflict participants' proximity to one another (in 1 m increments), visual contact (unobscured line of sight between the conflict participants), behavior exhibited, partner (if behavior was interactive), directionality of behavior (actor, receiver, or mutual), and presence of ASL at 20-sec intervals for the 10 min post-conflict and matched control periods. The first affiliative interaction after a conflict was recorded for all post-conflict and matched control periods. Observers obtained a minimum of 90% inter-observer reliability with an experienced observer recording behavioral contexts, proximity, reciprocity, and the occurrence of ASL in interaction.

During the 1998, 1999 (a and b), and 2000 (a and b) data collection periods conflict data were recorded. Data collectors recorded the initiator and recipient of a conflict, beginning time of conflict, duration of conflict, level of conflict intensity, and a narrative description of the conflict. Data collectors achieved 90% inter-observer reliability with an experienced observer recording the presence of conflict and level of conflict intensity prior to the data collection period. We defined conflict intensity by four levels. Level 1 consisted of directed threat behavior with no physical contact. Level 2 consisted of aggressive hits or kicks. Level 3 involved repeated hits/kicks, dragging and/or grappling, and Level 4 consisted of biting and/or physical contact resulting in observable injury (blood, broken skin, etc.).

A conflict event was defined as an aggressive interaction involving agonistic contact or three or more agonistic behaviors directed at another chimpanzee. End of a conflict event was defined as the cessation of aggressive behaviors between conflict participants. However if aggressive behaviors between conflict participants were observed within 2 min of the end of the original conflict, this was considered a false start. Observers waited until the cessation of aggressive behavior and then recorded post conflict (PC) data. Corresponding matched-control observations were conducted on the next observation day. These 10-min MC observations began at the same time of day and involved the same individuals as PC observations (see VEENEMA et al., 1994).

Reconciliation, consolation, redirection, and opponent proximity were examined by comparing "attracted" and "dispersed" pairs. If opponents interacted affiliatively earlier, or only, in the PC then they were termed "attracted" and the interaction was scored as reconciliation in the PC. If the affiliative interaction was earlier, or only, in the MC period then the opponents were termed "dispersed" (see VEENEMA, 2000). If an opponent-third party affiliative interaction was


recorded in the post-conflict period then the matched control period was examined for opponent-third party affiliative interaction. If the pair was termed "attracted" (see above) the consolation was considered to have occurred. Inter-opponent proximity was measured as closer sooner in the PC than the MC (attracted) or closer sooner in the MC than in the PC (dispersed). Maintenance of visual contact was scored based on the 30 20-sec scans recorded during the PC and MC periods. Conciliatory tendency was calculated by dividing the attracted pairs by the total number of conflicts. Corrected conciliatory tendency (CCT) was calculated by subtracting the dispersed pairs from the attracted pairs and dividing the result by the total number of conflicts (VEENEMA, 2000; VEENEMA et al., 1994). Consolation, redirection, and proximity tendencies were calculated in the same manner (with attracted pairs exhibiting the behavior in question only or first in the PC, dispersed pairs only or first in the MC and neutral pairs not at all). Consolation and redirection dyads where humans were participants (separated by enclosure bar- riers) were also included. In calculating the proximity tendency conflict pairs that were deter- mined to be either attracted or dispersed through social interactions (see CCT calculation above) were excluded from this independent analysis of proximity. Statistical analyses presented here were conducted via Chi-square tests, Wilcoxon signed ranks tests and z-tests for proportions with a significance level of p<.05.

RESULTS

CONFLICT DATA

A total of 219 conflicts (224 conflict pairs) were examined (1998 - 2000 collection periods). One hundred and twenty-nine conflicts consisted of aggressive hits or kicks (Level 2). Eighty- three conflicts consisted of directed threat behavior with no physical contact (Level 1). Twelve conflicts involved repeated hits/kicks, dragging and/or grappling (Level 3). No conflicts resulted in serious injury during the data collection periods, however at least three Level 4 conflicts occurred during non-data collection periods between 1998 and 2000. The range of conflict duration was 2 - 120 sec, with an average conflict duration of 15 sec.

In Figure I we depict the distribution of conflict within the chimpanzee's enclosure. The majority of conflicts occurred in the East room. The chimpanzees had full access to the outdoor portion of the enclosure during the summer observation periods, however during the 1999a and 2000a observation periods access was primarily limited to the indoor rooms due to frequent outdoor temperatures below 0°C.

POST-CONFLICT AND MATCHED CONTROL DATA

Post-conflict and matched control data were collected for a total of 255 conflicts (262 conflict pairs). Table 2 presents the total post-conflict and matched-control data set for the six collection periods between 1997 and 2000. Data are presented for reconciliation, consolation, redirection, and proximity for both the MC and PC observation periods (see methods for description of how these measures were calculated). Table 3a presents the number of conflicts per dyad and the corrected conciliatory tendency for that dyad. This was calculated by subtracting dispersed from attracted conflicts involving a dyad and dividing by the total conflicts for that dyad. Dyads were significantly more likely to be attracted following conflict than dispersed (T=3.5, n= 10, p<.05). The mean corrected conciliatory tendency across all dyads is 17.25 %. There is a nonsignificant negative correlation (Spearman's Rho= -0.354, n= 10) between con-

Conflict and Post-conflict Behavior

Fig. 1. Distribution of conflicts at CHCI 1998 - 2000b.

I Night Area 1

West I East 29 ~ 1 6 5

227

flict rate per dyad and Corrected Conciliatory Tendency. Different intensity level conflicts also

varied by Corrected Conciliatory Tendency. Table 3b presents individual corrected conciliatory tendencies, and Table 3c presents the cor-

rected conciliatory tendencies by age/sex class and is compared with the same measures published by PREUSCHOVr et al. (2002). While these chimpanzees reconciled an average of 17.5% of all conflicts across dyads, individual dyads ranged in corrected conciliatory tendencies (range

- 3 - 37.5%). Table 4 presents the results of this study along with the other published chimpanzee post-

conflict data. While frequency of participation in conflict varied, proportional participation remained fairly

consistent throughout the study. Loul is , the youngest male was involved in the highest number of conflicts (87%). The other chimpanzees participated less frequently: D a r (46%), Washoe

(32%), Tatu (31%), and M o j a (9%). Table 5 presents the percentages of total conflicts in which redirection, consolation, inter-

Table 2. Total post-conflict data 1997 - 2000.*

Conflicts Reconciliation Consolation Redirection Proximity 255 PC 39 PC 105 PC 80 PC 176

(262conflict pairs) MC 15 MC 93 MC 21 MC 83

*Bad observations were recorded for proximity data on two conflicts in 1998 and one conflict in 1999a. PC: In post- conflict only or first (attracted pairs); MC: in matched-control only or first (dispersed pairs).

Table 3a. Number of conflicts per dyad and Corrected Conciliatory Tendency (CCT) between individual conflict pairs (attracted-dispersed/total conflicts for that pair).

Dar Loulis Moja Tatu Washoe

Dar - 90 (4.4%) 5 (20%) 13 (30.8%) 3 (-33%)* Loulis - - 9 (33%) 50 (10%) 78 (3.8%) Moja - - - 8 (37.5%) 3 (33%) T a t u . . . . 3 (33%) Washoe . . . . .

*A negative CCT is reported for this dyad due to a higher frequency of dispersal following the observed conflicts.

228

Table 3b. Corrected Conciliatory Tendencies for each individual.

A. FUENTES et al.

Subject CCT

Dar 8.1% Loulis 6.4% Moja 32% Tatu 17.6% Washoe 5.8%

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CCT Across 17.25% Dyads

Table 3c. Corrected Conciliatory Tendency by age/sex class dyad at CHCI compared with PREUSCHOFT et al. (2002) values same age/sex classes.

Age/sex class CHCI (this study) Yerkes (PREUSCHOI~ et al., 2002)

Adult male-Adult male 4.4% NA Adult male-Adult female 16.3% 45.7% Adult female-Adult female 34.5% 57.9%

Table 4, Description of reconciliation and Corrected Conciliatory Tendencies in captive chimpanzee studies.

Corrected Conciliatory Species Location/setting Group size Opponent pairs Reconciliation Tendency Pan troglodytes Arhem l)

Indoor, 1979 20 150 34.7% - Outdoor, 1979 20 200 29.5% - Outdoor, 1981 20 95 26.6% - Detroit 2) Indoor/Outdoor, 1994 11 43 49.7% 14.4% CHCI 3) Indoor~Outdoor 5 262 25. 1% 17.25% 1997 - 2000 Budongo 4) Free Ranging, Uganda 51 120 19.2% Yerkes 5) 16 401 44.8% 41.2% Outdoor

Pan paniscus San Diego Zoo 6) Indoor/Outdoor, 1987 6 333 43.8% Outdoor, 1997 4 179 55.9%

1) DE WAAL • VAN ROOSMALEN, 1979; GRIEDE, 1981; 2) BAKER ~¢. SMUTS, 1994; 3) This study; 4) ARNOLD & WHITEN 2001; 5) PREUSCHOI'q" et al., 2002; 6) DE WAAL, 1987.

opponent proximity, and ma in tenance of visual contact were recorded for both PC and MC periods across the entire data col lect ion session. See MALONE et al. (2000) for a detailed description of redirection and consolat ion in this group of chimpanzees .

Because of the heavy representat ion of one individual we analyzed the data for consolat ion and redirection excluding the individual (Loulis) as an actor (and as recipient in the case of con-

solation). This produced the same patterns as the pooled data: no s ignif icant difference for con-

solation PC or MC (z=.62, n.s.) and significantly more redirect ion after conflicts (PC) than

during matched controls (MC) (z=3.72, p<.01). Proximity (closer sooner in PC vs closer sooner in MC) was also analyzed across dyads, the

Conflict and Post-conflict Behavior 229

Table 5. Group totals for redirection, consolation, overall proximity, and maintenance of visual contact for both PC and MC expressed as a percentage of total conflicts.

PC MC PC vs MC (chi-square test)

Consolation 40.0% 35.9% NS Redirection 30.5% 8.0% p < .01 Proximity (closer sooner) 67.2% 31.7% p < .05 Maintenance of visual contact 79.1% 64.6% p < .01

Table 6, Individual and group patterns for behaviors exhibited significantly more often in the PC than in the MC periods (p < .01).

Dar Loulis Moja Tatu Washoe Group Agonism 3 Affinitive Social I, 4 2 Bad Observation 4 5 Coprophagy 2, 3, 5 2, 3, 5 Display l, 2, 3, 5, 6 2, 3, 5, 6 l, 2, 3, 5, 6 Feeding 6 l, 6 3 6 Groom 3 4 4 Play 4 l l, 4 Object Manipulation 3 4 2 3, 4, 6 3, 4 Other 5 2 2 Reassurance 3 3 Self groom 3, 5, 6 3, 4, 5 1 3 6 3, 5, 6 Threat 5 1,2,4,5,6 3 1,2,5,6 1,2,4,5,6 Travel 2 1, 4 3 1, 2, 4

1: 1997; 2: 1998; 3: 1999a; 4: 1999b; 5: 2000a; 6: 2000b.

results show that conflict participants were more likely to be closer after a conflict than in a matched control period (T=0, n=7, p<.05).

Table 6 presents the behaviors that were exhibited significantly more often in the PC period by individuals and at the group level. A total of 16 behaviors were exhibited significantly more frequently in the PC period by one or more individuals across one or more of the data collection

sessions, and a total of 11 behaviors were exhibited significantly more often at the group level during the PC period. Only two behaviors were exhibited in five of the six data collection sessions significantly more often in the PC than the MC by the group (p<.0)). These behaviors

were "Display" and "Threat."

DISCUSSION

CONFLICT DATA

Interactions leading up to conflicts at CHCI include rough play behavior, disputes over a

favored object or location, and territorial displays (directed towards humans). Because of the

small size of this group and its long-term stability our initial expectations were that very few serious conflicts would occur. The overall conflict rate of approximately one conflict every

three observation hours bears this out. The majority of conflicts were of low to moderate intensity (Levels 1 and 2). However, this does not imply that conflict is not important at the CHCI.


That measurable behavioral patterns emerged after conflict by group members indicate that even low intensity conflict may be an important social stimulus (see SCHINO et al., 1998; VAN SCHAIK • AURELI, 2000).

ARNOLD and WHITEN (2001) found a non-significant trend in their free-ranging study of chimpanzees suggesting that conciliatory tendency is negatively correlated with conflict intensity (they report a mean CT of 36.1% for low intensity conflicts and a mean CCT of 16.7% for high intensity conflicts). Additionally, PREUSCHOFr et ai. (2002) also report more lower level than higher level intensity conflicts in their study of captive chimpanzees at Yerkes Regional Primate Research Center.

During this study one individual was a participant in the vast majority of recorded conflicts. This fact probably impacts the post-conflict behavior strategies utilized by the other group members. Loulis is the youngest male and appears to hold a high rank in the group (SANZ et al., 1995). Interestingly, PREtJSCHOVr et al. (2002) also report that a young male (a subadult in their case) participated disproportionately in conflicts. However, when we remove Loulis from the data set we still see the same patterns in consolation and redirection behavior which suggests that Loulis' impact may not be dramatically changing other chimps' behavior strategies. While this disproportionate representation of one individual in the conflict data stands out in a small group it is important to note that conflict participation may vary dramatically by individual in many situations across many primate groups.

The majority of recorded conflicts occur in the East room. A thick cement wall separates this room from the inner areas of the research facility wherein 15 - 50 people are frequently moving about involved in research and classroom activities. It is possible that the location, or structural aspects, of this area directly influence the high number of conflicts seen here.

POST-CONFLICT DATA

The results presented here share both similarities and differences with the other reports of chimpanzee post-conflict behavior (ARNOLD & WHITEN, 2001; BAKER & SMUTS, 1994; DE WAAL, 1987, 1989, 1993; DE WAAL & AtJRELI, 1996; DE WAAL & VAN ROOSMALEN, 1979; PREUSCHOFr et al., 2002). Our results do reinforce recent reports of variation within and across primate groups (ARNOLD & WHITEN, 2001; AtJRELI & SMtJCN¥, 2000; CASTLES et al., 1996; CORDS & KILLEN, 1998; PREOSCnOVr & VAN SCnA1K, 2000; SCnINO et al., 1998; THIERRV, 2000). While it is apparent that the dyads observed in this study do reconcile nearly a fifth of their conflicts, individual variation across dyads, and the variable post-conflict behavior observed combined with the variation in reported chimpanzee CCTs from other studies suggests that these chimpanzees may utilize an array of behavior, in addition to reconciliation, when negotiating conflict.

RECONCILIATION

Unlike previous studies of captive chimpanzees we did not observe a specific set of overt affiliative behavior occurring after conflicts (see DE WAAL & VAN ROOSMALEN, 1979; DE WAAL, 1989, 1993; PREUSCr~ovr et al., 2002). The one reported free-ranging study of chimpanzee post- conflict behavior (ARNOLD & WHITEN, 2001) also reports a lack of a clear and discernable char- acteristic set of reconciliatory behaviors. While embracing was observed as an affiliative behavior involved in reconciliation, we did not observe frequent kissing, holding out of hand, or submissive vocalizations. This may be due to the relatively small number of reconciled conflicts [24 (attracted - dispersed) out of 262 opponent pairs]. Alternatively, this may be because differ-


ent groups of chimpanzees may exhibit differing post-conflict affiliative behavior ("cultural" differences: see MCGREW, 1998; WHITEN et al., 1999; and differences in age, sex, kin relations, group history: see ARNOLO & WHITEN, 2001 ).

Given that four of the five chimpanzees in this group were cross-fostered, it is possible that this has an impact on their post-conflict behavior. However, only a few chimpanzee studies have been conducted using the PC/MC control method and the correction factor proposed by VEENEMA et al. (1994) which subtracts the baseline affiliation from post-conflict affiliation. Therefore it is difficult to make specific comparisons and assertions about baseline chimpanzee reconciliation behaviors. Two other published studies on captive chimpanzees (Detroit Zoo: BAKER & SMUTS, 1994; Yerkes: PREUSCHOFF et al., 2002) and one on free-ranging chimpanzees (Budongo: ARNOLD • WHITEN, 2001) provided corrected conciliatory tendencies or contained sufficient published information allowing us to calculate the corrected conciliatory tendency. The Detroit Zoo study, the study at Budongo, and this study result in fairly low corrected conciliatory tendencies of between (14.4 and 19.2%). PREUSCHOFT et al. (2002) report a higher CCT (41.2%). However, one must be extremely careful when reporting group level corrected conciliatory tendencies, as they may not accurately reflect the underlying individual variation, and it is not clear that a mean score effectively represents a trend or group behavioral pattern.

Individuals varied in their rates of reconciliation, most notably by conflict participant. One female, Moja, engaged in the lowest number of conflicts (25) yet reconciled 32% of them. Loulis, on the other hand, participated in a high number of conflicts (227) with reconciliation occurring after very few of them (6.4%). This trend of lower CCT with increasing conflict frequency was also found by PREUSCHOFT et al. (2002). Individuals in the CHCI group ranged between 5.8 and 32% in corrected conciliatory tendencies. The only comparable numbers for chimpanzees come from the PREUSCHOFT et al. (2002) study and are generally higher (20 - 69.2%). However, the PREUSCHOFT et al. (2002) study contained eight immature individuals and eight adults, including only one adult male. Additionally, only three of the eight adults participated in 20 or more conflicts (AM Jimoh: 31 conflicts; AF Mai: 25 conflicts; AF Anja: 28 conflicts). If we examine only these three adults the CCTs are 38.7, 20, and 50% respectively (the PREUSCHOFT et al., 2002), giving a 36.2% mean corrected conciliatory tendency. It is very possible that the different composition of the groups at CHCI and Yerkes make direct comparisons of the databases difficult.

In addition to individual corrected conciliatory tendencies we also examined dyads by age/sex class. Female-female dyads had a substantially higher CCT than did male-male or het- erosexual dyads. Again there is difficulty comparing these numbers to PREUSCHOFT et al. (2002) due to the demographics of the two groups and the differential in adult-adult conflict pairs (262 at CHCI and 52 at Yerkes). However, female-female pairs had the highest corrected conciliatory tendencies in both studies.

The inter-individual variation in reconciliation may be related to the relationships amongst those individuals (ARNOLD & WHITEN, 2001 ; CORDS & AURELI, 2000; PREUSCHOFT et al., 2002). At the CHCI there is variation across individual dyads in rates of reconciliation. For example, the two lowest ranking individuals, who often interact affiliatively, had the highest dyadic CCT (37.5%). This may reflect aspects of the "relationship quality" factor that is suggested to be associated with an increased likelihood of dyadic reconciliation (ARNOLD & WHITEN, 2001; PREUSCHOFT et al., 2002).

There is a difference across conflict Levels 1 and 2 in conciliatory tendencies. This may be due to the differential intensity (no physical contact in Level 1 and physical contact in Level 2). Alternatively, this differential may be an artifact of frequency, as Level 2 conflicts where nearly twice as common as Level 1. While the current low number of Level 3 conflicts prevents a


more effective assessment of the relationship between conflict intensity and reconciliation it is interesting to note that SCHINO et al. (1998) found no significant differences between reconciliation related to the lowest ("threats") and the highest ("physical assault") conflict categories in a group of Macaca fuscata.

REDIRECTION

Re-directed aggression occurred significantly more often during post-conflict periods than matched control periods. The majority of redirection can be attributed to one individual (Loulis) and 63% of all redirection was directed towards human caretakers (see MALONE et al., 2000, for a detailed description).

CONSOLATION

Although affiliation occurred after conflicts, individuals did not engage in affiliative behavior with third parties more so after conflicts than in matched control observations. However, it may be relevant to note that 97 (48.9%) of the 198 potential consolation events in the PC and MC were with human partners. The lack of significant difference in PC and MC consolation might suggest that for this group of chimpanzees consolation is not a common strategy for negotiating conflict. This reduced role for consolation is supported by the free-ranging study at Budongo (ARNOLO & WHITEN, 2001) where a lack of consolation after conflict was also reported. We are currently examining the directionality of initiation of consolation behavior across all data collection periods in an effort to more accurately assess third part post-conflict contact (i.e. DAS, 2000).

PROXIMITY

Conflict partners were spatially closer to one another sooner and more often during post-conflict observations than matched-control observations. This suggests an active manipulation of space use following conflicts. One possible explanation for this result is that spatial proximity and neutral behavior may be act as a peaceful post-conflict signal (SILK, 1996, 1998, 2000). Therefore, remaining close and behaviorally neutral (not affiliative and not agonistic) may be sufficient to clearly indicate the cessation of a conflict and the conflict participants' intent to not engage in further conflict at the present time (DE WAAL & YOSHIHARA, 1983). ROWELL and OLSON (1983) suggested that a change in spatial position communicated a change in social relationship. Close proximity may allow a conflict partner to monitor their opponents' movements and adjust their position accordingly. Alternatively, CORDS and AURELI (1993, 2000) reported that maintaining close proximity after a conflict restored a functional aspect of a social relationship.

VISUAL CONTACT

Visual contact between the conflict participants was significantly more common in the PC than the MC period for this study. Overall this finding suggests that individuals may be actively keeping the conflict partner in visual contact and monitoring his/her behavior. If signals of benign intent, or some alternative functional signal, are communicated soon after a conflict it would be very important for conflict participants to maintain visual contact.


POST-CONFLICT BEHAVIORS

At the group level the behaviors "threat" and "display" were exhibited significantly more often after conflicts than during matched control observations across five of the six data collection sessions. This is due primarily to the behavioral contributions of Washoe and Loulis for whom threat and display were common behaviors after conflicts. Interestingly, travel is a significant post-conflict behavior at the group level for three of the four summer data collection sessions but is absent at the group level during the 1999a and 2000a (winter) data collection sessions when space was limited. This may indicate that individuals shift their pattern of behavior as the available the space changes (JUDGE, 2000).

It is important to note that each individual exhibits specific behaviors significantly more often in the PC periods across data collection periods and that three of the five individuals do not appear to be consistent in these behaviors across the study (see Table 6). While this may be a reflection of the sample size for each data collection period, it might also reflect slight differences in group relationships, individual's health, weather conditions, and other variables impacting these chimpanzees.

CONCLUSION

This group of chimpanzees did reconcile approximately 17% of their conflicts. However, individual variation in corrected conciliatory tendencies was large, suggesting that the mean CCT may not accurately represent the strategies used by the individual chimpanzees in this group. Individuals exhibited a range of behaviors, visually monitored former opponents, redirected aggression and maintained increased proximity following conflicts. They did not appear to seek or give consolation after conflicts. These results, combined with the relatively low corrected conciliatory tendencies from the one other captive (BAKER & SMUTS, 1994) and one free- ranging study (ARNOLD & WHITEN, 2001) suggest that post-conflict behavior aside from reconciliation may also be important to our understanding of chimpanzee conflict negotiation. Given the variation in mean corrected conciliatory tendencies across the four published studies (see Table 4) and the individual variation in CCT reported here and by PREUSCHOFT et al. (2002) it is important to continue and expand on the investigations into chimpanzee behavior following conflicts. In light of increased evidence of relationship qualities on post-conflict behavior patterns and the modifiability of reconciliatory behavior through social experience a broader approach to conflict negotiation studies in chimpanzees is needed (ARNOLD & WHITEN, 2001; CORDS & AURELI, 2000; DE WAAL & AURELI, 2000; PREUSCHOFT et al., 2002). Our data suggest that proximity/use of space, visual monitoring, redirection of aggression, conflict pairs' relationships, and aspects of the captive environment may be important facets in the conflict negotiation of this small group of chimpanzees.

Acknowledgements. We wish to thank Dr. ROGER FOUTS and DEBORAH FOUTS, Co-Directors of the Chimpanzee and Human Communications Institute at Central Washington University, for their support and encouragement. We thank all of the CHC| apprentices, students and staff who worked long and hard col- lecting and entering the data, without them this project could not have taken place. We also wish to thank Dr. F1LIPPO AURELI, Dr. ROBERT SUSSMAN, MARCEL HARVEY, and two anonymous reviewers for comments and suggestions on various drafts of this manuscript. Finally, we wish to thank the chimpanzees of the CHCI, Washoe, Loulis, Dar, Moja, and Tatu for making this project possible.


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- - Received: July 24, 2001; Accepted: April 24, 2002

Authors' Names and Present Addresses: AGUSTIN FUENTES, Department o[Anthropolog); Notre Dame University, Notre Dame, hMiana 46556-5639. U. S. A. e-mail: [email protected]; NICHOI.AS MAI.ONI-, Primate Behavior and Ecology Program, Central Washington University, Ellensburg, Washington 98926-7544, U. S. A.; CRICKI;lq'I~ SANg, Department c~l: Anthropolog); Washington Universit3; St. Louis, Missouri, U. S. A.; MEGAN MATHESON, Primate Behavior and Ecology Program and Department o, f Psycholog3; Central WashhNton University Ellensburg, Washington 98926-7544. U. S. A.; LORIt~N VAU(~HAN, San Diego WiM Animal Park, San Diego. Cal[/ornia, U. S. A.

conflict and post-conflict behavior in a small group of chimpanzees 13

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