Ravens reconcile after aggressive conflicts with valuable partners

Reconciliation, a post-conflict affiliative interaction between former opponents, is an important mechanism for reducing the costs of aggressive conflict in primates and some other mammals as it may repair the opponents' relationship and reduce post-conflict distress. Opponents who share a valuable relationship are expected to be more likely to reconcile as for such partners the benefits of relationship repair should outweigh the risk of renewed aggression. In birds, however, post-conflict behavior has thus far been marked by an apparent absence of reconciliation, suggested to result either from differing avian and mammalian strategies or because birds may not share valuable relationships with partners with whom they engage in aggressive conflict. Here, we demonstrate the occurrence of reconciliation in a group of captive subadult ravens (Corvus corax) and show that it is more likely to occur after conflicts between partners who share a valuable relationship. Furthermore, former opponents were less likely to engage in renewed aggression following reconciliation, suggesting that reconciliation repairs damage caused to their relationship by the preceding conflict. Our findings suggest not only that primate-like valuable relationships exist outside the pair bond in birds, but that such partners may employ the same mechanisms in birds as in primates to ensure that the benefits afforded by their relationships are maintained even when conflicts of interest escalate into aggression. These results provide further support for a convergent evolution of social strategies in avian and mammalian species.     

Reconciliation following aggression in patas monkeys,Erythrocebus patas

Following intra-group aggression, obvious conciliatory displays are absent from the behavioural repertoire of patas monkeys, Erythrocebus patas, while many other Old World primate species show special reconciliation gestures. When 10-min focal-animal samples that began after spontaneous aggression were compared with matched-control samples, captive adult female patas followed up on aggressive interactions, interacting sooner and more often with former opponents during post-conflict observations than during matched-control observations. Almost one-third of post-conflict observations included affiliative behaviour between former opponents, which is termed reconciliation. Matrilineally related opponents were more likely to reconcile with one another than were unrelated animals. No effect of the dominance hierarchy on tendency to reconcile was found. Thus, patas monkeys showed general patterns in post-conflict behaviour that were similar to those seen in other primates previously investigated.     

Testing the function of reconciliation and third-party affiliation for aggressors in hamadryas baboons (Papio hamadryas hamadryas)

In social groups, agonistic conflicts can have different negative consequences. Several post-conflict interactions have been suggested as post-conflict management behaviors to mitigate those negative effects. In this study, we investigated the function of two post-conflict behaviors--reconciliation and aggressor-initiated third-party affiliation--on the aggressor's levels of post-conflict anxiety and aggression in a large colony of hamadryas baboons. We also examined variation in the aggressor's levels of post-conflict anxiety as a function of relationship quality between the opponents as predicted by the Integrated Hypothesis. We found that after conflicts hamadryas baboon aggressors showed increased rates of anxiety-related behaviors and that they were also more likely to be involved in renewed aggressive interactions. Although both reconciliation and aggressor-initiated third-party affiliation reduced the probability of receiving post-conflict aggression, only reconciliation reduced the rates of anxiety-related behaviors, suggesting that the aggressors' post-conflict anxiety might be owing mainly to the damage that the conflict causes to their relationship with the victim. Furthermore, aggressor's rates of post-conflict anxiety were higher after conflicts with individuals with whom they had a high-quality relationship, supporting the idea that levels of post-conflict anxiety mediate the occurrence of reconciliation depending on the quality of the relationship with former opponent as predicted by the Integrated Hypothesis.     

Reconciliation and the Costs of Aggression in Wild Barbary Macaques (Macaca sylvanus): A Test of the Integrated Hypothesis

The ‘integrated hypothesis’ predicts that reconciliation (the post‐conflict friendly interaction between former opponents observed in various group‐living species) functions to reduce anxiety and the risk of aggression from the former opponent or a bystander in the aftermath of a conflict. It also predicts that relationship quality between opponents affects the occurrence of reconciliation and modulates the anxious response of the opponents after a conflict. Because of the asymmetric nature of aggressive interactions, the cost of aggression is likely to differ between the victim and the aggressor. The aim of this study was to test the predictions of the ‘integrated hypothesis’ independently for the victim and the aggressor of a conflict. We collected data on two wild groups of Barbary macaques. This study represents, to our knowledge, the first systematic test of the integrated hypothesis on wild, non‐provisioned animals. Victims of aggression were at a greater risk of receiving aggression from the former opponent or a bystander after a conflict and showed elevated anxiety. We found no such costs for the aggressor. Reconciliation reduced anxiety in the victim but did not reduce their risk of receiving aggression. Finally, relationship quality affected the occurrence of reconciliation but did not modulate post‐conflict anxiety. The results of our study show that the costs of aggression are asymmetrically distributed between the victim and the aggressor. Such differences are likely to lead to different social tactics used by the victim and the aggressor in the aftermath of a conflict.     

The function of peaceful post-conflict contacts among primates

Reconciliation has been the subject of considerable research in the last decade, and researchers have demonstrated that in many species of Old World monkeys and apes former opponents are more likely to engage in friendly interactions in the minutes that follow conflicts than they are at other times.de Waal has suggested that the function of these interactions is to mend relationships that have been damaged by conflict. Although peaceful post-conflict interactions are thought to have long-term effects upon the nature of social relationships, behavioral evidence presently indicates that the effects of these interactions may be limited to the post-conflict period. Theoretical considerations also raise some doubts about whether the relationship-repair hypothesis is cogent. Data that demonstrate that peaceful post-conflict interactions facilitate peaceful interactions and relieve victim's uncertainty and anxiety about whether conflict will be continued suggest that peaceful post-conflict interactions may be a means to reestablish contact with former opponents. Thus, they appear to function as predictive signals that the actor is going to stop fighting and behave peacefully. Such signals may be important in a broad range of social contexts.     

Post-conflict Social Events in Wild Mountain Gorillas (Mammalia,Hominoidea). I. Social Interactions between Opponents

Researchers have documented elevated rates of affinitive interaction between opponents shortly after aggressive conflicts, or reconciliation, in many primate species. Reconciliation may ameliorate the immediate negative effects of aggression by reducing the chance of further aggression between opponents and thus reducing tension, and may avert or repair damage to long-term social relationships important to the animals' fitness. Data on post-conflict interactions between opponents in two groups of wild mountain gorillas (Gorilla gorilla beringei) fail to show reconciliation after conflicts between females, between males, or between immatures, but females seem to commonly reconcile themselves with males after receipt of male aggression. Females and subordinate males often avoid same-sex opponents after conflicts. Females commonly retaliate against female aggressors, and post-conflict rates of aggression between females are higher than baseline levels. Females may not need to achieve reconciliation with each other because relationships between co-resident relatives are resiliant, while those between non-relatives are mostly neutral to antagonistic. Males are, however, important social partners and protectors of females, and female transfer is common. Thus, the results strongly support the ‘important relationships’ hypothesis for the function of reconciliation.     

Post-Conflict Affiliation in Barbary Macaques is Influenced by Conflict Characteristics and Relationship Quality, but Does Not Diminish Short-Term Renewed Aggression

Many group living primates have evolved mechanisms to repair their social relationships after conflicts ('reconciliation'). We analysed the post-conflict behaviour of female Barbary macaques, Macaca sylvanus , living in the enclosure 'La Forêt des Singes' at Rocamadour, France. Based on a sample of 914 conflicts, we investigated whether relationship (kinship, rank, affiliation, support and sex) and conflict characteristics (conflict intensity, context and duration) affected the quality and frequency of affiliative post-conflict interactions. Thirty-two per cent of all conflicts were followed by post-conflict affiliation. Rates of socio-positive interactions and support were better predictors of post-conflict affiliation than kinship or rank. Short conflicts were followed by post-conflict affiliation relatively more frequently, after a shorter latency, but only briefly, and such interactions were initiated by both parties equally frequently. The majority of affiliative post-conflict interactions occurred immediately after the end of the conflict. In sum, female Barbary macaques invest more in post-conflict affiliation with valuable partners, and they modulate their post-conflict behaviour in relation to conflict characteristics. Remarkably, affiliative post-conflict interactions increased the short-term probability of renewed aggression by the former aggressor to 16% compared with 9% for conflicts that were not followed by affiliative behaviour. Such renewed aggression after post-conflict affiliation occurred particularly frequently among females and after conflicts over food, suggesting that post-conflict affiliation sometimes falsely lures the former victim to stay in the vicinity, even at the risk of receiving renewed aggression.     

Post-conflict affiliation by chimpanzees with aggressors: other-oriented versus selfish political strategy

Consolation, i.e., post-conflict affiliation directed from bystanders to recent victims of aggression, has recently acquired an important role in the debate about empathy in great apes. Although similar contacts have been also described for aggressors, i.e., appeasement, they have received far less attention and their function and underlying mechanisms remain largely unknown. An exceptionally large database of spontaneous conflict and post-conflict interactions in two outdoor-housed groups of chimpanzees lends support to the notion that affiliation toward aggressors reduces the latter's aggressive tendencies in that further aggression was less frequent after the occurrence of the affiliation. However, bystander affiliation toward aggressors occurred disproportionally between individuals that were socially close (i.e., affiliation partners) which suggest that it did not function to protect the actor itself against redirected aggression. Contrary to consolation behavior, it was provided most often by adult males and directed toward high ranking males, whereas females engaged less often in this behavior both as actors and recipients, suggesting that affiliation with aggressors is unlikely to be a reaction to the distress of others. We propose that bystander affiliation toward aggressors may function to strengthen bonds between valuable partners, probably as part of political strategies. Our findings also suggest that this post-conflict behavior may act as an alternative to reconciliation, i.e., post-conflict affiliation between opponents, in that it is more common when opponents fail to reconcile.     

Reconciling conflicts in a one-male society: the case of geladas (<Emphasis Type="Italic">Theropithecus gelada</Emphasis>)

Animals derive benefits from living in social groups but sociality also has its costs in that animals must compete with others for resources and mating opportunities. To cope with the conflict aftermath and social damage caused by competitive aggression, several group-living species use a variety of peace-keeping strategies. The affinitive post-conflict reunion of former opponents, defined as reconciliation, is the primary peace-keeping mechanism. In this study, we provide evidence for the occurrence of reconciliation and test some hypotheses on this post-conflict mechanism in geladas (Theropithecus gelada), a species often neglected in the study of post-conflict dynamics. The conciliatory contacts were uniformly distributed across the different sex–class combinations. Different from baboons, geladas did not show any particular kind of affinitive reconciliation behaviour. Notwithstanding the presence of a linear hierarchy, the dominance relationships did not affect the reconciliation dynamics. According to the valuable relationship hypothesis, coalitionary support seems to be a good predictor for a high level of conciliatory contacts. Finally, at an immediate level reconciliation plays a role in reducing renewed attacks by aggressors, which sought conciliatory contact more frequently than victims. In conclusion, even though the study of post-conflict behaviour in geladas needs to be continued, the patchy nature of their social network is a good model for testing some of the theoretical assumptions about primate conflict resolution.     

Reconciliation in captive Guyanese squirrel monkeys (Saimiri sciureus)

The tendency for agonistic interaction to increase the probability of friendly interaction between social partners has been demonstrated across a range of Old World primates. While research on such post-conflict behavior proceeds into an hypothesis-testing phase, new comparative information must accumulate to provide full phylogenetic perspective on primate social behavior. Data from New World and prosimian primates are yet extremely limited. We studied captive squirrel monkeys (Saimiri sciureus) via post-conflict (PC) and matched control (MC) observations and analyzed results using both the PC-MC and time-rule methods. Former opponents maintaining affiliative relationships soon engaged in friendly interaction following large proportions of agonistic interactions, whereas non-affiliated individuals, including virtually all male-female pairs, reconciled conflicts rarely. Close-proximity approaching and huddling contact constituted the principal modes of post-conflict amicability. Agonistic interactions of relatively high intensity were most likely to be reconciled and most likely to be reconciled via physical contact. High vulnerability of Saimiri to predation may have favored this species' strong inclination to reconcile soon after agonistic interaction. Research on free-living populations of this and other primate species is needed to illuminate similarities and differences across taxa.     

Postconflict third-party affiliation in rooks, Corvus frugilegus

Conflict features in the lives of many animal species and induces social stress mediated by glucocorticoid hormones [1]. Postconflict affiliation, between former opponents (reconciliation) or between former opponents and a bystander (third-party affiliation), has been suggested as a behavioral mechanism for reducing such stress [2], but has been studied almost exclusively in primates [3]. As with many primates, several bird species live in social groups and form affiliative relationships [4]. Do these distantly related animals also use affiliative behavior to offset the costs of conflict? We studied postconflict affiliation in a captive group of rooks. Unlike polygamous primates, monogamous rooks did not reconcile with former opponents. However, we found clear evidence of third-party affiliation after conflicts. Both initiators and targets of aggression engaged in third-party affiliation with a social partner and employed a specific behavior, bill twining, during the postconflict period. Both former aggressors and uninvolved third parties initiated affiliative contacts. Despite the long history of evolutionary divergence, the pattern of third-party affiliation in rooks is strikingly similar to that observed in tolerant primate species. Furthermore, the absence of reconciliation in rooks makes sense in light of the species differences in social systems.     

Post-conflict Behaviour of Wild Olive Baboons. II. Stress and Self-directed Behaviour

Previous studies indicate that the proximate function of post-conflict affiliative interaction among primates is to reduce a victim's uncertainty about its opponent's future behaviour: the ‘uncertainty reduction hypothesis’ (Aureli & van Schaik 1991; Ethology, 89 , 101–114). This study confirms and extends these results, demonstrating that they are neither a product of captivity nor specific to macaques: both victims and initiators of aggression in a large group of wild olive baboons exhibited elevated rates of self-directed behaviour (SDB) - scratching, autogrooming, body-shaking and yawning - in a 10-min post-conflict period. During this period, they were more likely to receive further aggression. Reconciliation reduced both SDB and the incidence of further aggression. However, reconciliation only reduced SDB among individuals involved in conflicts in which both parties exchanged aggression. It is suggested that aggressors in unilateral conflicts were aroused rather than uncertain and that their victims' lack of control over post-conflict interactions (which tended to be initiated by their opponents) prevented them from benefiting from reconciliation in the same fashion as longtailed macaque victims, which frequently initiated reconciliation.     

Single Aggressive Interactions Increase Urinary Glucocorticoid Levels in Wild Male Chimpanzees

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.     

The effect of inter-opponent distance on the occurrence of reconciliation in stumptail (Macaca arctoides) and rhesus macaques (Macaca mulatta)

Several studies have shown that affiliative contact between opponents increases after conflicts in a number of primate species. This study investigated the effect of inter-opponent distance on the occurence of reconciliation in stumptail and rhesus macaques. Both species were represented by multi-male, multi-female groups housed in large outdoor compounds. Ten-minute focal animal observations during post-conflict (PC) and matched control (MC) samples were collected in which affiliative interactions and the inter-opponent distance at the beginning of each sample were recorded. A total of 251 and 561 PC-MC opponent pairs were obtained for stumptail and rhesus macaques, respectively. Inter-opponent distance was smaller in PC than in MC observations for both stumptail and rhesus macaques. Conciliatory tendency varied as a function of the initial PC-MC inter-opponent distance. In particular, the closer opponents were in PC compared to MC periods, the more likely they were to reconcile. When the inter-opponent distance was the same in PC and MC periods the conciliatory tendency of both species was notably reduced. These findings have implications for the estimation of conciliatory tendency and its use in comparative studies.     

Post-conflict Behaviour of Wild Olive Baboons. I. Reconciliation,Redirection and Consolation

Observations of post-conflict interactions have provided important insights into primate social organization. In this study, the nature and determinants of post-conflict behaviour in a troop of wild olive baboons, Papio anubis, were investigated. Reconciliation was observed among all age-sex classes, occurring at a rate consistent with a relatively intolerant dominance style. Reconciliation was more frequent when one of the combatants carried a dependent infant but rarely followed conflicts associated with food. Neither the directionality nor the decidedness of conflicts affected conciliatory tendency. In contrast, opponents that were close kin or of similar rank reconciled more often. Olive baboons did not affiliate with non-combatants more frequently following aggression than in control periods, although affiliation with supporters and the close kin of opponents increased. Absence of consolation follows the observed cercopithecine pattern, consistent with the hypothesis that consolation requires an ability to empathize with the victim's distress. Initiation of post-conflict attacks on third parties was not elevated in victims of aggression. The rarity of redirection is attributed to spatial dispersion, the frequent bidirectionality of baboon aggression and regular male intervention in female conflicts, all of which appear to limit the availability of ‘safe’ targets.     

Grooming coercion and the post-conflict trading of social services in wild Barbary macaques

In animal and human societies, social services such as protection from predators are often exchanged between group members. The tactics that individuals display to obtain a service depend on its value and on differences between individuals in their capacity to aggressively obtain it. Here we analysed the exchange of valuable social services (i.e. grooming and relationship repair) in the aftermath of a conflict, in wild Barbary macaques (Macaca sylvanus). The relationship repair function of post-conflict affiliation (i.e. reconciliation) was apparent in the victim but not in the aggressor. Conversely, we found evidence for grooming coercion by the aggressor; when the victim failed to give grooming soon after a conflict they received renewed aggression from the aggressor. We argue that post-conflict affiliation between former opponents can be better described as a trading of social services rather than coercion alone, as both animals obtain some benefits (i.e. grooming for the aggressor and relationship repair for the victim). Our study is the first to test the importance of social coercion in the aftermath of a conflict. Differences in competitive abilities can affect the exchange of services and the occurrence of social coercion in animal societies. This may also help explain the variance between populations and species in their social behaviour and conflict management strategies.     

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

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.     

Following the rules: why small groups of tamarins do not reconcile conflicts

Reconciliation is the post-conflict friendly reunion between opponents. A series of conditions and rules in order for reconciliation to take place has been recently proposed. One critical condition is that the relationship between opponents must be disrupted. We tested this condition using post-conflict and matched-control observations on 4 small groups of tamarins (Saguinus labiatus). Our previous lack of evidence for reconciliation was confirmed. No post-conflict relationship damage was therefore expected. We found evidence that relationships were disturbed following conflicts over food but, as in other primates, no evidence for reconciliation following such conflicts was found. For non-food-related conflicts there was no evidence that relationships were disturbed, as opponents were in close proximity to each other and resumed the exact same activity as frequently in the post-conflict observations as they did in the matched-control observations. We conclude that 'everyday' aggression may not disrupt the relationships among individuals from the same family group and therefore reconciliation is not needed.     

A Statistical Modelling Approach to the Occurrence and Timing of Reconciliation in Wild Japanese Macaques

In various social species, animals have been observed to share friendly relationships with some group members and to resolve conflicts through reconciliation, the exchange of affiliative behaviour soon after a conflict that functions to restore the relationship between the former opponents. The valuable relationship hypothesis predicts that reconciliation should be observed more often after conflicts between friends. Friendly relationships can be described by three dimensions (i.e. value, security and compatibility); however, research into the relative importance of these dimensions for the occurrence of reconciliation is sparse. Moreover, reconciliation may depend on factors other than the social relationship between opponents including, for example, their social status or the context of the conflict. Our study aimed at analysing which factors are important determinants of reconciliation and at testing the valuable relationship hypothesis, by analysing the relative effects of relationship value, security and compatibility on the occurrence and timing of reconciliation. We collected data on two troops of wild Japanese macaques living on Yakushima Island, Japan, and selected the best predicting variables of reconciliation using linear mixed models. Our results show that reconciliation occurs more frequently, and earlier, after conflicts between opponents who exchange a higher percentage of grooming. Two additional variables related to relationship security and value were selected in the best models: frequency of aggression and of approaches resulting in tolerated co‐feeding. Among the variables not related to relationship quality, distance between opponents at the end of the conflict, kinship, sex of the opponents and context of conflict (i.e. during feeding or social time) were included in our models. Our findings support the valuable relationship hypothesis and, in particular, highlight that the fitness‐related benefits of social relationships (i.e. the relationship value) are important determinants of the evolution of friendly relationships and reconciliation.     

Patterns of reconciliation among captive gelada baboons (Theropithecus gelada): A brief report

Animals that live in groups are frequently exposed to conflict situations and must in some way maintain group cohesion. One mechanism that appears to restore social relationships after they have been disrupted by conflict isreconciliation. This study investigated reconciliatory behavior in the gelada baboon,Theropithecus gelada. The subjects were 11 adult geladas, housed in a large outdoor enclosure at the Bronx Zoo/Wildlife Conservation Park, New York. Five-minute focal animal samples following spontaneous aggression were compared with 5-min matched-control samples. The results of this study were: (1) geladas reunited in a friendly way after aggression; (2) former opponents were attracted to one another rather than dispersed from one another after a conflict; (3) most post-conflict reunions occurred within the first 2 min of the post-conflict period; and (4) geladas do not have any specific types of behavior associated with post-conflict reunions as do chimpanzees and macaques. The results of this study support the hypothesis that gelada baboons reconcile after aggression.