Abstract: Bystanders are capable of extracting cues from signalling interactions between others and appear to use information gained via eavesdropping when confronted with the watched individuals. A question that has gained little attention is whether observing fights affects bystander behaviour outside the context of interacting with the watched individuals. Our aim was to determine whether watching fights elicits general changes in bystander aggression levels in Xiphophorus helleri. We manipulated the bystanders' ability to witness encounters using clear, one-way-mirror and opaque partitions. After watching (or not watching) an initial contest, the bystanders were pitted against naive conspecifics instead of the animals they had seen fight. Observing fights did not alter the bystanders' propensity to initiate aggression, escalate, or win against naive individuals, indicating that bystanders do not experience general changes in aggressive behaviour after watching a fight. Earlier work in this species, however, has shown that bystanders respond in predictable ways to individuals they have witnessed winning or losing a fight. Taken together, these data support the notion that bystanders consistently modify their behaviour towards previously watched winners or losers in response to information gained via eavesdropping. We discuss our results in light of some recent work on the behavioural and endocrinological responses triggered by watching fights and suggest that comparative approaches to understanding networking phenomena may be productive.

Abstract: Following aggressive interactions, dominant female baboons, Papio cynocephalus ursinusoccasionally grunt to their victims. To examine the effect of these apparently reconciliatory grunts on victims' subsequent behaviour, a series of playback experiments was designed to mimic reconciliation. Victims were played their opponents' grunts in the minutes immediately following a fight and then observed for half an hour. After hearing these grunts, victims approached their former opponents and also tolerated their opponents' approaches at significantly higher rates than they did under control conditions. They were also supplanted by their opponents at significantly lower rates. By contrast, playbacks of control females' grunts did not influence victims' behaviour. Playbacks of reconciliatory grunts did not increase the rate at which opponents approached or initiated friendly interactions with their former victims. Playbacks of reconciliatory grunts, therefore, appeared to influence victims', but not opponents', perception of recent events.

Abstract: We performed two experiments in which we allowed a male fighting fish, Betta splendens, designated a bystander, to observe aggressive contests between pairs of male conspecifics. Another male (naive male) observed an empty tank or two nonaggressive males, depending on the experiment. Immediately after these observation periods, we allowed the bystander and naive male to interact in a neutral area. In both experiments, bystander males were dominant over naive males in a significant number of the encounters. Bystander males performed significantly more aggressive behaviours (displays, chases and bites) than did naive males. Differences in dominance were not due to chance differences in body size. These findings demonstrate that exposure to aggression between conspecifics increases aggressive motivation in bystander male fighting fish. We discuss briefly the implications of such social experience on the formation of dominance hierarchies. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Abstract: Stumptailed macaques, Macaca arctoides, are characterized by high levels of postconflict affiliative contacts between opponents. We investigated the occurrence of postconflict affiliative contacts between opponents and third parties that were not involved in the original conflict. We collected 10-min focal observations during postconflict and control periods in which we recorded all aggressive and affiliative behaviours between opponents and third parties. We distinguished three types of third parties depending on the relationship with the focal animal: own kin, opponent's kin and individuals unrelated to both opponents. We analysed the interactions with third parties separately, while distinguishing two classes of affiliative behaviours: (1) allogrooming and contact sitting and (2) sociosexual behaviours (e.g. genital inspection). The macaques showed differences between postconflict and control periods in their affiliative contacts with third parties. Aggressors received more postconflict grooming and contact sitting from their opponents' kin, received more sociosexual behaviour from their own kin and unrelated individuals, and directed more sociosexual behaviour to unrelated individuals. Victims received and directed less postconflict grooming from and towards their own kin. They received more postconflict sociosexual behaviour from all partners except their own kin and directed more sociosexual behaviour to all partners except the opponent's kin. This study establishes the occurrence of multiple postconflict triadic affiliation in stumptailed macaques, and is the first to show that victims receive contacts from third parties in a cercopithecine species, a behaviour previously described only in chimpanzees. It also highlights the importance of analysing the different affiliative behaviours separately in postconflict situations. Otherwise, many of the patterns we report, especially those involving victims, would have been missed.

Abstract: Females often aggregate at particular sites for feeding or shelter, thus giving adult males the opportunity to defend harems and increase male reproductive success. Rival males compete for control of harems via ritualized displays or direct combat using weaponry. Contests for harems or the resources required by females can be settled based on asymmetries in fighting ability or resource ownership. Males that accurately assess a rival's fighting ability prior to engaging in potentially costly combat should be favoured by selection. Game theory and optimality models provide three models to explain how individuals decide to persist in or flee from a fight. These models are the energetic war of attrition, the sequential assessment model and the cumulative assessment model. Using staged contests in the laboratory, I tested predictions of these models using the Wellington tree weta, Hemideina crassidens, a sexually dimorphic insect native to New Zealand. Male H. crassidens use their enlarged mandibles as weapons in fights for access to adult females that reside in cavities in trees. My results supported a prediction common to each assessment model: contest duration was negatively correlated with the asymmetry in opponent's weapon size. The sequential assessment model of contest settlement was partially supported but the strongest support was for the cumulative assessment model. Predictions of the latter model were supported because: (1) fights are apparently settled based on own-size assessment; (2) fights occur in a single phase and escalate; and (3) contests involve physical combat and injury. I suggest that, in nocturnal species, cumulative assessment will generally be most applicable.