The Structure of Bonobo Copulation Calls During Reproductive and NonReproductive Sex

During mating events, numerous mammals and birds produce loud and acoustically distinct vocalisations, usually referred to as ‘copulation calls’. In some species, males are the main producers (e.g. little brown bats, Myotis lucifugus, Barclay & Thomas 1979), but generally they are given by females, sometimes accompanied by their male partner (e.g. elephant seals, Mirounga angustirostris, Cox & Le Boeuf 1977; African elephants, Loxodonta africana, Poole et al. 1988). Copulation calls are widespread among primates, particularly in multi-male multi-female Old World species, in which females mate promiscuously and advertise their receptivity with pronounced sexual swellings (Dixson 1998). The prevalence and conspicuous nature of female copulation calls has evoked considerable interest and a broad array of adaptive hypotheses has been put forward (Pradhan et al. 2006). Essentially, all converge on the theme that copulation calls are sexually selected signals that promote the caller’s reproductive success (e.g. Maestripieri & Roney 2005). For example, copulation calls may advertise sexual receptivity (e.g. Semple 1998, 2001), allowing a female to accrue mate choice benefits by inciting male–male competition, either directly (Cox & Le Boeuf 1977) or indirectly via sperm competition (O’Connell & Cowlishaw 1994). Copulation calls may also reduce threats of infanticide (Pradhan et al. 2006) by promoting paternity uncertainty or enhancing mate guarding (O’Connell & Cowlishaw 1994). In chimpanzees (Pan troglodytes), females are vulnerable to infanticide by both males (e.g. Muller et al. 2007) and other females (Townsend et al. 2007). In a recent study, it was found that chimpanzee females called most when mating with high-ranked males, possibly as a means to confuse paternity and enlist their future Correspondence Zanna Clay, Living Links, Yerkes Primate Research Center, Emory University, Atlanta, GA 30322, USA. E-mail: [email protected]