Ecology rather than psychology explains co-occurrence of predation and border patrols in male chimpanzees

Ian C. Gilby, Michael L. Wilson, Anne E. Pusey

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23 Scopus citations


The intense arousal and excitement shown by adult male chimpanzees, Pan troglodytes, during territorial attacks on other chimpanzees and predation upon monkeys suggest that similar psychological mechanisms may be involved. Specifically, it has been proposed that hunting behaviour in chimpanzees evolved from intraspecies aggression. Over 32 years, chimpanzees at Gombe National Park, Tanzania were significantly more likely to engage in a territorial border patrol on days when they hunted red colobus monkeys (. Procolobus spp.), and vice versa, even after statistically controlling for male chimpanzee party size. We test the hypothesis that this correlation arises because hunting and patrolling are components of a species-level aggressive behavioural syndrome; specifically that predation arose as a by-product of territorial aggression in this species. However, hunting was equally likely to occur after a patrol and/or an intergroup interaction as it was before, and the occurrence of an intergroup interaction in which the chimpanzees approached strangers did not increase subsequent hunting probability. We also reject the hypothesis that hunting and patrolling reflect an individual-level behavioural syndrome. We identified two 'impact hunters' whose presence increased hunting probability. Similarly, there were also three 'impact patrollers', who increased the likelihood that a visit to the periphery of the community range resulted in a patrol. While this discovery has important implications for our understanding of the proximate causes of cooperation, it does not explain the temporal correlation between patrolling and hunting, since no males had such an impact in both contexts. Instead, the data suggest that the correlation arose because patrols typically involved males travelling long distances, which increased the probability of encountering prey. Additionally, parties that travelled to the periphery were more likely to encounter colobus in woodland, where hunts are more likely to occur and to succeed. Therefore, we conclude that ecological, rather than psychological, factors promote the co-occurrence of hunting and territorial aggression in this species.

Original languageEnglish (US)
Pages (from-to)61-74
Number of pages14
JournalAnimal Behaviour
Issue number1
StatePublished - Jul 2013

Bibliographical note

Funding Information:
Data collection was funded by the Jane Goodall Institute (JGI) . Digitization and analysis of behavioural data were supported by grants from the National Science Foundation ( DBS-9021946 , SBR-9319909 , BCS-0452315 , BCS-0648481 , LTREB-1052693 ), the National Institutes of Health ( R01 AI50529 , R01 AI58715 , P30 AI 27767 ), the University of Minnesota , the Harris Steel Group , the Windibrow Foundation , the Jane Goodall Institute , the Carnegie Corporation , Minnesota Base Camp and Duke University . We thank TANAPA, TAWIRI and COSTECH for permission to work in Gombe National Park, and the tireless Gombe Stream Research Center staff for maintaining data collection. Many thanks to Ross Bernstein, Jason Beyer, Burke Bourne, Kelly Hughes, Katie Lee, Doug Ludeman, Deus Mjungu, Kim Neu, Alphonce Nicholaus, Nathan O'Neil, Miranda Oliver, Kevin Potts, Anne Scheuerman, Joann Schumacher-Stankey, Elma Stapic, Andrea Vidmar, Marta Wernikiewicz and Anna Wynn for assistance with data extraction. Finally, we are extremely grateful to Lilian Pintea for development of the vegetation map.


  • Behavioural syndrome
  • Chimpanzee
  • Collective action
  • Cooperation
  • Hunting
  • Impact males
  • Lethal aggression
  • Pan troglodytes
  • Territoriality


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