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Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates (1-5). Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning (6-9). To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported., Substantial variation exists in rates of killing across chimpanzee study sites (2-5,10-12). The human impact and adaptive strategies hypotheses both seek to explain this variation, but have contrasting predictions, which [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2008.11.021 Byline: John C. Mitani Abstract: Controversy exists regarding the nature of primate social relationships. While individual primates are frequently hypothesized to form enduring social bonds with conspecifics, recent studies suggest that relationships are labile, with animals interacting only over short periods to satisfy their immediate needs. Here I use data collected over 10 years on a community of chimpanzees, Pan troglodytes, at Ngogo, Kibale National Park, Uganda, to investigate whether male chimpanzees establish long-term social relationships and to determine the factors that affect variation in relationship quality and the stability of social bonds. Kinship and dominance rank influenced the quality of relationships. Maternal brothers and males of the same dominance rank class groomed each other more equitably than did unrelated males and males that were dissimilar in rank. In addition, males that formed strong social bonds groomed more equitably than did males that displayed weaker bonds. Social bonds were stable over time, with relationships in one year predicting those in subsequent years. Kinship and the quality of social relationships affected bond stability. Maternal half siblings and males that groomed each other equitably maintained longer-lasting bonds than did nonkin and males that groomed each other unevenly. Virtually all of the males established at least one enduring relationship with another individual. The most enduring bonds formed between a few pairs of maternal brothers and dyads that maintained balanced grooming interactions. These results indicate that male chimpanzees maintain long-lasting and equitable social bonds whose formation is affected by maternal kinship and the quality of social relationships. Author Affiliation: Department of Anthropology, University of Michigan, U.S.A. Article History: Received 29 September 2008; Revised 28 October 2008; Accepted 18 November 2008 Article Note: (miscellaneous) MS. number: A08-00627R

The complex cooperative behavior exhibited by wild chimpanzees generates considerable theoretical and empirical interest, yet we know very little about the mechanisms responsible for its evolution. Here, we investigate the influence of kinship on the cooperative behavior of male chimpanzees living in an unusually large community at Ngogo in Kibale National Park, Uganda. Using long-term field observations and molecular genetic techniques to identify kin relations between individuals, we show that male chimpanzees clearly prefer to affiliate and cooperate with their maternal brothers in several behavioral contexts. Despite these results, additional analyses reveal that the impact of kinship is limited; paternal brothers do not selectively affiliate and cooperate, probably because they cannot be reliably recognized, and the majority of highly affiliative and cooperative dyads are actually unrelated or distantly related. These findings add to a growing body of research that indicates that animals cooperate with each other to obtain both direct and indirect fitness benefits and that complex cooperation can occur between kin and nonkin alike. Pan troglodytes | genotyping | kin recognition | microsatellites | relatedness

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2005.02.012 Byline: John C. Mitani, David P. Watts Abstract: Territorial boundary patrols are a distinctive and unique aspect of wild chimpanzee, Pan troglodytes, behaviour. Although patrolling has been frequently observed in nature and several proposed functional explanations for it exist, scant information is available regarding the proximate factors that affect this activity. We found that there is considerable temporal variation in the frequency of patrolling by chimpanzees at Ngogo, Kibale National Park, Uganda. We examined several ecological and social factors that potentially influence this variation. Results of logistic regression analyses revealed that male party size was the single best predictor of the tendency to patrol. Lethal intergroup aggression occurs in chimpanzees, and patrols are likely to be dangerous and costly. Our findings are consistent with the hypothesis that chimpanzees at Ngogo reduce these costs by patrolling together in large parties. Author Affiliation: (a) Department of Anthropology, University of Michigan (a ) Department of Anthropology, Yale University Article History: Received 9 September 2004; Revised 27 November 2004; Accepted 3 February 2005 Article Note: (miscellaneous) MS. number: A9992

A study aims on several ecological and social factors that potentially influence the terrestrial boundary patrols that are a distinctive and unique aspect of wild chimpanzee behaviour. The study revealed that the male party size were the single best predictors of the tendency to patrol and lethal intergroup aggression occurs in chimpanzees and patrol are likely to be dangerous and costly.

Research is presented of a study of wild adult male chimpanzees in Uganda that tests the extent to which matrilineal genetic relatedness affects male social cooperation and affiliation patterns. Significant correlation is found in six behavioural measures.

An experiment exploring the contexts and social corellates of long-distance calling by male chimpanzees, Pan troglodytes, was conducted. The long-distance call is characterized by the pant-hoot. Results from observations indicate that high travel engenders more calls, higher status chimpanzees emitted more calls than lower ranking chimpanzees. Chimpanzees hooted more frequently in the presence of alliance partners.

Encounters and associations between adult male, adult female and subadult male orang-utans, Pongo pygmaeus, were examined at the Kutai National Park and Gunung Palung Nature Reserve, Indonesia. Observed rates of encounters, durations of associations and proportions of time spent in associations of two members of each age-sex class from each population were compared with expected values generated from null models of associations. Encounter rates, durations of associations and proportions of time spent in associations were greater than expected by chance. Two factors appear to generate these non-random patterns: subjects at both sites met conspecifics at food sources more often than expected, and associations frequently involved social behaviour. Three differences in association patterns existed between populations. Orang-utans at Kutai encountered each other more frequently, engaged in longer associations, and spent a greater proportion of time together than conspecifics at Gunung Palung. Variations in association patterns between populations reflected age-sex class differences in behaviour. In contrast to adult and subadult males at Kutai, males at Gunung Palung avoided conspecifics. Similarly, adult females and subadult males at Gunung Palung spent less time with others than did their Kutai counterparts. An analysis of the nature of associations revealed two additional behavioural differences between populations. Mating did not occur at Gunung Palung, but was observed frequently at Kutai, and subadult males at Kutai received aggression, while those at Gunung Palung did not. These data support the hypothesis that variations in the reproductive states of adult females account for differences in the patterns of association between orang-utans. Sociality among orang-utans appears primarily the result of aggregation at common resources, either food or mates.

Two lethal coalitionary intergroup attacks on adult males at the Ngogo research site in Kibale, as well as severe attacks on an adult male and a juvenile male that were almost certainly fatal are described. It is suggested that lethal coalitionary aggression between groups is part of the natural behavioral repertoire of chimpanzees and is consistent with the 'food defense' hypothesis.

The new demographic records of chimpanzees from Mahale are presented. The factors that affect chimpanzee reproduction and their conservation are discussed.

Researchers observed a large community of chimpanzees at Ngogo, Kibale National Park, Uganda, to determine factors affecting affiliation and cooperation among males of the group. The results suggest that male chimpanzees of the same age class and rank are more likely to affiliate and cooperate than males belonging to different age and rank groups. The results also confirm earlier findings that maternal kinship does not bias affiliation and cooperation behavior.

A new study of chimpanzees seeks to determine the factors influencing their hunting and meat sharing decisions. Three common hypotheses are tested.

We investigated hunting in an unusually large community of wild chimpanzees at Ngogo in the Kibale National Park, Uganda. Aspects of predation were recorded with respect to the prey, the predators, and hunting episodes. During 23 months of observation, the Ngogo chimpanzees caught 128 prey items from four primate and three ungulate species. Chimpanzees preyed selectively on immature red colobus primarily during group hunts, with adult males making the majority of kills. Party size and composition were significant predictors of the probability that chimpanzees would hunt and of their success during attempts. Chimpanzees were more likely to hunt red colobus if party size and the number of male hunters were large; party size and the number of male hunters were also significantly larger in successful compared with unsuccessful hunts. The Ngogo chimpanzees did not appear to hunt cooperatively, but reciprocal meat-sharing typically took place after kills. Hunts occurred throughout the year, though there was some seasonality as displayed by periodic hunting binges. The extremely high success rate and large number of kills made per successful hunt are the two most striking aspects of predation by the Ngogo chimpanzees. We compare currently available observations of chimpanzee hunting behavior across study sites and conclude that the large size of the Ngogo community contributes to their extraordinary hunting success. Demographic differences between groups are likely to contribute to other patterns of interpopulation variation in chimpanzee predation. KEY WORDS: Pan troglodytes; predation; primates