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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.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.

Leptin is considered to act as a signal relating somatic energetic status to the reproductive system. However, the nature of that signal and its relationship with male reproductive function across nonhuman primate species are unclear. We suggest that species-specific differences in leptin physiology may be related to the degree of environmental variation and variation in the importance of energy stores for male reproduction. In order to test the role of seasonality in species differences among nonhuman primates, we compared leptin, testosterone, and body composition in male rhesus (n = 69) and pig-tailed (n = 43) macaques. Despite having larger abdominal fat deposits, the rhesus macaques did not exhibit significantly higher leptin levels (rhesus, 2.21 [+ or -] 0.43 ng/ ml; pig-tailed, 2.12 [+ or -] 0.39 ng/ml). Both species showed increases in leptin across adolescent, subadult, and adult age-groups (P = 0.036 for rhesus; P = 0.0003 for pig-tailed by ANCOVA). Testosterone was not significantly associated with leptin in either the rhesus (r = 0.039; P = 0.754) or pig-tailed (r = 0.2862; P = 0.066) samples. Comparison of leptin levels across the two species using univariate modeling procedures showed no significant age-group by abdominal fat interaction. These findings suggest little difference in leptin production between these two closely related species, despite the difference in breeding seasonality. KEY WORDS adiposity; energetics; primate mass index; Macaca mulatta; Macaca nemestrina; contest competition

Infanticide by Males and Its Implications, edited by C.P. van Schaik and C.H. Janson. Cambridge, UK: Cambridge University Press, 2000. 584. pp. $43.60 (paperback); $116.50 (hardback). The claim that infanticide [...]

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.

Hormone-behavior interactions in a sample of wild male chimpanzees, quantified testosterone in 67 fecal samples obtained from 22 adult male chimpanzees at Ngogo, Kibale National Park, Uganda are discussed. The utility of fecal samples and a mixed-model statistical method for behavioral endocrinology studies is 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