The function of seasonal song in a tropical resident species, the Red-throated Ant-tanager (Habia fuscicauda)

Recent studies of tropical birds with year-round territoriality indicate that song rate is relatively low year-round in association with lower seasonality and relatively stable social environment over the year. We examined seasonal variation in the song rate of Red-throated Ant-tanagers (Habia fuscicauda), a socially monogamous species in which males predominantly sing during the breeding season, to determine to what extent increased song rate is driven by (1) increased territory defense, (2) pair coordination of nest initiation, and (3) competition for extra-pair mating opportunities. Song was infrequent during the non-breeding season, increased dramatically prior to nesting (17 % time spent singing), and increased even more so during nesting (32 % time spent singing). Male song output was inversely related to frequency of interactions between pairs at territorial borders; however, interactions may also serve in a mating context. Extra-pair matings were common, and 17 of 41 nestlings in ten of 19 broods were extra-pair young, suggesting that high male song output may be sexually selected via extra-pair mate choice. Although males spent much less time singing prior to nesting, our results also indicate that male initiation of singing was associated with female egg-laying date, indicating also a role in within-pair coordination of reproduction. Our results suggest that high song output during the breeding season may be more common in omnivorous species that experience increased seasonality and that it may be indicative of an extra-pair mating system. More studies of species with diverse life histories are needed to examine the ecological conditions that explain interspecific variation in song output.