Nice guys finish last: same-sex sexual behavior and pairing success in male budgerigars

In budgerigars (Melopsittacus undulatus), a social parrot in which females are socially dominant, males of all ages engage in a set of behaviors with other males that closely resembles the repertoire used in heterosexual courtship. One adaptive hypothesis for this tendency, the "courtship practice hypothesis," posits that males with greater experience in same-sex activities develop superior skills that increase their courtship success with females. To test this hypothesis, we measured individual variation in tendency of subadult males to engage in such behaviors and asked whether birds' relative participation in same-sex activities predicted adult pairing success in competitive pairing trials conducted after birds reached adulthood. Males' tendency to participate in same-sex activities was correlated across samples collected a month apart. Directly contrary to the courtship practice hypothesis, however, males that participated in same-sex interactions more often were less likely to obtain mates. Pairing success was also predicted by 2 sexually dimorphic facial traits, namely iris prominence and cere color. We hypothesize that the tendency of males to engage in same-sex interactions may represent a mechanism of mutual assessment of male abilities, especially those involved in group foraging efforts (the "leader assessment hypothesis") and suggest that increased investigation of allopreening and other seemingly affiliative behaviors that occur outside the heterosexual pair bond may advance understanding of social organization in flocking birds.