American Journal of Primatology 71:919–927 (2009) RESEARCH ARTICLE Vigilance in Ursine Black and White Colobus Monkeys (Colobus vellerosus): An Examination of the Effects of Conspecific Threat and Predation ANDREW J.J. MACINTOSH 1Ã AND PASCALE SICOTTE 2 1 Section of Social Systems Evolution, Kyoto University Primate Research Institute, Inuyama-shi, Aichi-ken, Japan 2 Department of Anthropology, University of Calgary, Calgary, Alberta, Canada Vigilance is thought to have evolved as an antipredator defense but, in primates, conspecific threat often better explains this behavior. We examined vigilance in one group of Colobus vellerosus inhabiting the Boabeng-Fiema Monkey Sanctuary in Ghana. We aimed to (1) describe factors affecting vigilance in this population, and (2) examine the importance of predation avoidance and conspecific threat in explaining vigilance patterns. Because of a male takeover preceding the study, our focal group (B2) consisted of six adult males and three adult females. We collected 490 10-min focal samples (82 hr) from all adults in the group (N 5 9) from July to November, 2001. To avoid predators, individuals should be more vigilant (i) with fewer neighbors, and (ii) in areas of the canopy with higher predation risks. Conspecific threats can be divided into extra- and intra-group threats. Extra-group threats should lead to higher vigilance levels (iii) during intergroup encounters, and (iv) in areas where the home range overlaps with other groups of colobus. Intra-group threats should lead to greater vigilance (v) in the presence of neighbors and (vi) while feeding or occupying food patches (if resources are limiting). Our results best support the hypothesis that vigilance functions primarily to detect extra-group, conspecific threats. Individuals were most vigilant during intergroup encounters and in areas of range overlap, and monthly vigilance rates were associated with monthly encounter rates. Individuals tended to scan less in proximity to familiar vs. unfamiliar group mates, suggesting that relationship quality may affect colobus vigilance. Finally, predation pressures or anthropogenic disturbances might have influenced vigilance, as individuals were more vigilant low in the canopy. However, this last result could also be due to the lower visibility because of dense foliage or to the fact that the monkeys have access to fewer escape routes when ranging lower in the canopy. Am. J. Primatol. 71:919–927, 2009. r 2009 Wiley-Liss, Inc. Key words: black and white colobus; vigilance; conspecific threat; infanticide; predator avoidance INTRODUCTION Models of animal vigilance have focused mainly on the impact of predation pressures on individual vigilance behavior [Alexander, 1974; Bertram, 1978; Caro, 2005; Elgar, 1989; Pulliam, 1973; Roberts, 1996]. Recently, social factors have also been shown to affect this behavior in various species [Cameron & Du Toit, 2005; Childress & Lung, 2003; Hirsch, 2002; Kutsukake, 2006, 2007; Lung & Childress, 2007; Monclus & Rodel, 2008; Panozzo et al., 2007]. Primate vigilance in particular is affected by social factors. While many studies did find predation avoidance to be an important function of primate vigilance [Cords, 1990; Kutsukake, 2006; van Schaik & van Noordwijk, 1989; Steenbeek et al., 1999], several have failed to support the most commonly observed pattern in the vigilance behavior of social animals, that is, that individual vigilance decreases as group size increases [see Caro, 2005; Treves, 2000]. In fact, a host of social and demographic factors have been shown to affect vigilance in primates, some of which are probably population and habitat-specific (Table I). Colobines are ideal subjects for investigating the influences of social factors and in particular the effect of conspecific threat on individual vigilance, as male mating competition and infanticide have long been reported in Asian colobines [Borries, 1997; Hrdy, 1974; Steenbeek, 2000; Struhsaker & Leland, 1987; Sugiyama, 1965] and have recently been Published online 13 July 2009 in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ajp.20730 Received 10 January 2009; revised 14 June 2009; revision accepted 15 June 2009 Contract grant sponsors: Natural Sciences and Engineering Research Council of Canada; University of Calgary; Province of Alberta; Calgary Zoo Conservation Fund and Primate Conserva- tion Inc. Ã Correspondence to: Andrew J. J. MacIntosh, Section of Social Systems Evolution, Kyoto University Primate Research Insti- tute, 41-2 Kanrin, Inuyama-shi, Aichi-ken 484-8506, Japan. E-mail: macintosh@pri.kyoto-u.ac.jp r r 2009 Wiley-Liss, Inc.