IS MATE CHOICE COPYING OR AGGREGATION RESPONSIBLE FOR SKEWED DISTRIBUTIONS OF FEMALES ON LEKS

In several lek-breeding populations of birds and mammals, females arri ving on leks tend to join males that already have females in their ter ritories. This might occur either because females have an evolved pref erence for mating with males that are attractive to other females, or because they join groups of other females to obtain greater safety fro m predation or dangerous harassment by males. We have previously used controlled experiments to show that oestrous fallow deer females join males with established harems because they are attracted to female gro ups rather than to the males themselves. Here we demonstrate that the preference for males with females over males without females is specif ic to oestrous females and weak or absent in anoestrous ones, and that it is not associated with a preference for mating with males that hav e previously been seen to mate with other females. Furthermore, oestro us females given the choice between males that do not already have fem ales with them show no significant preference for antlered over deantl ered males or for older males over younger ones. We conclude that fema le attraction to other females on the lek is likely to be an adaptatio n to avoiding harassment in mixed-sex herds. In this situation, a male 's ability to maintain the cohesion of his harem may be the principal cause of variation in mating success between males.