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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

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

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.

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.