EXTRA-PAIR MATING SYSTEM OF A SYNCHRONOUSLY BREEDING TROPICAL SONGBIRD

Extra-pair matings are now recognized as a fundamental component of av ian mating systems. However, in tropical regions where breeding is typ ically asynchronous socially monogamous species appear to have low spe rm competition and few extrapair matings. We predicted that if breedin g synchrony promotes the evolution of extra-pair matings, then tropica l species that breed synchronously, like the Clay-colored Robin Turdus grayi, should have abundant extra-pair young (EPY). Breeding began re latively abruptly during the dry season (Feb-Mar) in this non-migrator y species, with a mean of 25% of females fertile on a given day. Overa ll, 53% of females produced EPY, and 38% of nestlings were EPY. Males have a long and conspicuous dawn chorus, which could be a result of in tense male-male competition for extra-pair matings. Male songs are ind ividually recognizable and males vary greatly in song output. Male son g output declined significantly from the pre-nesting stage through the incubation stage, as would be expected if song is important in mate c hoice. Our results support the idea that breeding synchrony favors ext ra-pair matings, however further studies of tropical songbirds are nee ded to fully explore how ecology is tied to extra-pair mating systems.