American Journal of Primatology 71:1–8 (2009) RESEARCH ARTICLE Intra-Community Coalitionary Lethal Attack of an Adult Male Southern Muriqui (Brachyteles arachnoides) M. G. TALEBI 1,2Ã , R. BELTRA ˜ O-MENDES 2,3 , AND P. C. LEE 4 1 Biological Sciences Faculty, Federal University of Sa˜o Paulo, Diadema, Estado de Sa˜o Paulo, Brazil 2 Pro´-Muriqui Association, Behavioral Biology and Conservation, Sa˜o Paulo, Sa˜o Paulo, Brazil 3 Department of Conservation & Ecology, Federal University of Sergipe, Sa˜o Cristova˜o, Sergipe, Brazil 4 Department of Psychology, University of Stirling, Stirling, Scotland We report on the first evidence of intra-community coalitionary lethal aggression in muriquis (Brachyteles). The event occurred in southern muriquis (Brachyteles arachnoides) during a long-term study (415 years) of two social groups inhabiting mostly pristine Atlantic forest habitat in the Parque Estadual Carlos Botelho, southern Sa ˜o Paulo State, Brazil. The attack took place deep in the core area of the Group Caete ˆ home range. Tense agonistic behaviors and vocalizations preceded the lethal coalitionary attack, and the tension increased over a 36–48 hr period. One adult female and two unidentified individuals also took part in a coalition led by six adult males. The members of the coalition collectively approached, embraced, immobilized and repeatedly bit the entire body of an adult male, resulting in severe bleeding injuries and the victim’s death in less than 1 hr after the attack commenced. Combined ecological, behavioral and spatial data related to the event indicate that this was an intra-community attack and suggest social tensions related to mating competition as the proximate trigger of the coalitionary killing. The attack resembled those reported for chimpanzees, with clear numeric superiority and a low risk of injury to aggressors, resulting in the death of a lone conspecific victim. This observation (n 5 1) is suggestive of a capacity for escalated aggression in muriquis and reinforces arguments for the potential adaptive significance of intra-community aggression in male philopatric societies, as reported for spider monkeys and chimpanzees. These characteristics challenge the view of the muriquis as a peaceful primate and support the general hypothesis that imbalances of power contribute to intra-specific killing in primates, such as chimpanzees and humans. Am. J. Primatol. 71:1–8, 2009. r 2009 Wiley-Liss, Inc. Key words: aggression; coalitions; male–male competition; muriquis; B. arachnoides INTRODUCTION Fatal wounding during contests between adult individuals, especially males, is widespread in mam- mals. Episodes of intra-specific killing have been reported for 132 mammal species in nine genera [Byers, 1997; Clutton-Brock et al., 1982]. Coalition- ary lethal attacks involving several individuals are, however, relatively rare, and are known from social carnivores [Mech, 1994] and some primate taxa: humans, chimpanzees, [Boesch et al., 2007; Watts, 2004; Wrangham, 1999], gorillas, red colobus, capu- chins [Grous-Louis et al., 2004] and spider monkeys [Campbell, 2006; Valero et al., 2006]. Intra-specific lethal coalitionary aggression has been related to both inter-community and intra-community compe- tition and though a number of events have been described, relatively little is yet known about the causation or functions of such nonhuman primate aggression [Boesch et al., 2007]. Chimpanzees live in multi-male multi-female so- cieties characterized by a high degree of fission–fusion dynamics, male philopatry, female dispersal and high levels of both male–male cooperation and high levels of male–male competition. In chimpanzees, disputes for food, females and fertilizations [Wrangham, 1987] have repeatedly resulted in coalitionary lethal attacks [Fawcett & Muhumuza, 2000; Watts, 2004; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ajp.20713 Received 11 November 2008; revised 27 April 2009; revision accepted 27 April 2009 Contract grant sponsor: CNPq, Brazilian National Research Council; Contract grant number: 20025699-8; Contract grant sponsors: WWF-IIE, Support for postgraduate studies; Conser- vac - a ˜o International (Brazil); ATBC Clifford Evans Grant; Margot Marsh Biodiversity Foundation; Primate Action Fund of Conservation International; MetroParks Zoo Cleveland, Idea Wild, Conservation Food and Health Foundation (USA); Manfred Hermsen Stiftung Foundation (Germany); Fauna & Flora International, DEFRA and Bromley Trust (UK). Ã Correspondence to: M. G. Talebi, Rua Luis Gois 1902 apto 73, Mirandopolis, Sa ˜o Paulo, CEP 04043-200, Brazil. E-mail: talebi@promuriqui.org.br, talebi@pq.cnpq.br r r 2009 Wiley-Liss, Inc.