THE FUNCTION OF BARBARY MACAQUE COPULATION CALLS

In a wide variety of animal species, females produce vocalizations spe cific to mating contexts. It has been proposed that these copulation c alls function to incite males to compete for access to the calling fem ale. Two separate advantages of inciting male-male competition in this way have been put forward. The first suggests that as a result of cal ling, females are only mated by the highest ranking male in the vicini ty (indirect mate choice hypothesis). The second proposes chat copulat ion calling results in a female being mated by many males, thus promot ing competition at the level of sperm (sperm competition hypothesis). In this paper, I give results from the first experimental study to tes t these hypotheses. Playback was used to examine the function of copul ation calls of female Barbary macaques (Macaca sylvanus) in Gibraltar. Although rank did not affect lone males' likelihood of approaching co pulation calls, when playbacks were given to pairs of males only the h igher ranking individual approached. Moreover, females were mated sign ificantly sooner after playback of their copulation call than after pl ayback of a control stimulus. These results suggest that the copulatio n calls of female Barbary macaques play a key role in affecting patter ns of male reproductive behaviour, not only providing an indirect mech anism of female choice, but also promoting sperm competition by reduci ng the interval between copulations. Potential fitness benefits of inc iting male-male competition at these two levels are discussed.