Anim. Behav., 1995, 49, 395–401 Kinship and association in communally roosting black vultures P. G. PARKER*², T. A. WAITE‡ & M. D. DECKER²§ *Department of Z oology, Ohio State University, Columbus, OH 43210, U.S.A. ² Department of Biological Sciences, Purdue University, W . Lafayette, IN 47907, U.S.A. ‡Behavioral Ecology Research Group, Department of Social Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 Canada ( Received 14 July 1993; initial acceptance 1 November 1993; final acceptance 2 February 1994; M S. number: 6755) Abstract. Black vultures, Coragyps atratus, spend each night in a communal roost, and individuals sleep at several different roosts over time. They feed in large aggregations at carcasses and engage in apparently cooperative behaviour within coalitions of individuals that co-occur predictably at both roosts and carcasses. Roost census data and DNA fingerprinting results were used to investigate whether black vultures tend to roost in the company of genetic relatives. Restricting the analysis to dyads of breeding adults that were the heads of known lineages and were not mated to one another, a positive correlation emerged between indices of the genetic similarity of individuals and their tendency to use the same roost on the same night. The results provide evidence of long-term associations between some closely related breeding adults, associations that appear not to be simply a consequence of natal philopatry but reflect the daily reassembly of coalitions at communal roosting sites. This social organization could facilitate the evolutionary stability of cooperation among communally roosting black vultures. Recent theoretical studies have focused attention on conditions that may yield evolutionarily stable cooperation between unrelated individuals (Axelrod & Hamilton 1981; Lima 1989; see also Dugatkin & Wilson 1991). None the less, it remains important in any study concerned with cooperative behaviour to ask whether the main- tenance of such behaviour may be partly attribut- able to inclusive fitness gains resulting from interactions between genetic relatives (Hamilton 1964; Wilson & Dugatkin 1991). Here we examine the genetic similarity of individuals from black vulture, Coragyps atratus, nuclear families that overlap in their use of communal roosts. Black vultures are non-territorial scavengers that search extensive areas for carcasses at which they form large aggregations. They sleep year- round in communal roosts containing dozens or even hundreds of individuals. Spatial and tempo- ral clumping of individuals departing from roosts and arriving at food (Rabenold 1983, 1987a), and following by individuals that are naïve to the location of recently discovered food sources (Rabenold 1987a), suggest that black vulture roosts serve as information centres (Ward & Zahavi 1973) from which unsuccessful foragers may follow successful foragers to known food sources. Although roost membership varies from night to night as individuals move among several roosts (Rabenold 1987b), coalitions consisting of several nuclear families of unknown relatedness co-occur consistently and interact in an appar- ently cooperative fashion while in larger groups at roosts and feeding sites (Rabenold 1986). Compe- tition between coalitions in contests over food may be the selective force favouring cooperation within coalitions. The development of molecular tools that allow researchers to assay genetic relatedness with fine resolution (Jeffreys et al. 1985a, b) has led to new insights into life histories of non-human animals (e.g. Burke & Bruford 1987; Rabenold et al. 1990), including those with intractable demogra- phies (Reeve et al. 1990; Packer et al. 1991; Wayne et al. 1991; Amos et al. 1993). In our study population, the earliest observed age of first breeding was 8 years, mean reproductive success once breeding was 1·3 young/pair/year, and §Present address: Department of Ecology, Evolution and Behavior, University of Minnesota, Minneapolis, MN 55455, U.S.A. 0003–3472/95/020395+ 07 $08.00/0  1995 The Association for the Study of Animal Behaviour 395