Males in several lekking species aggregate with their relatives to display for females, suggesting that kin selection can affect sexual selection. Several hypotheses have been proposed to explain this behavior, but no general explanation has emerged. In most species with lek mating systems, neighboring males have intense aggressive interactions that can affect the quality of their sexual displays. Here we test the hypothesis that the presence of related neighbors mitigates the negative consequences of this aggression. Male bowerbirds build stick display structures (bowers) that are used by females in mate assessment and are commonly destroyed by males' 2 nearest neighbors. We show that kin aggregate as first or second nearest neighbors, and males direct fewer bower destructions toward kin than equidistant nonkin. Males with more relatives nearby receive fewer bower destructions. These results suggest that the restraining effect of relatedness on aggression favors the close spatial association of related males' display sites. An alternative hypothesis, that related males aggregate to gain copulations from females attracted to successful relatives, was not supported.
