Male and female signaling behavior varies seasonally during territorial interactions in a tropical songbird

Abstract

In many tropical birds, both sexes use conspicuous vocal signals during territorial interactions. Although a growing number of studies examine male and female signals in the context of coordinated vocal duets, the use of vocal signals by both sexes in non-duetting species is poorly documented, even though these species are more numerous than duetting species. Furthermore, few studies of tropical non-duetting species test for seasonal variation in signaling behavior. We studied season-specific and sex-specific variation in signaling behavior of a tropical resident songbird, the Rufous-capped Warbler (Basileuterus rufifrons), by conducting a playback experiment where we simulated conspecific territorial intruders producing three types of vocalizations (male songs, female calls, or a “pair” with simultaneous male songs and female calls) and a heterospecific control. We repeated playback during the pre-breeding and breeding seasons. Response intensity to playback varied with season and sex of the focal birds. During the pre-breeding season, both sexes showed strong physical approach responses and vocal responses to all conspecific intrusions, especially paired intrusions. During the breeding season, males responded strongly to all conspecific treatments, whereas females showed little response. Although females primarily used calls in response to conspecific playback, many females also sang, especially during the non-breeding season. Our results therefore suggest that both male and female signals are used for shared territory defense, but that the contributions of each sex to territory defense vary seasonally. Our results also contribute to our understanding of the evolution of combined male and female signaling during territory defense. In resident tropical animals, both males and females often use conspicuous signals during territorial interactions with conspecifics. Seasonal and sex-specific variation in vocal behavior of tropical resident birds during these territorial interactions has received little research attention. We conducted a playback experiment to investigate season- and sex-specific variation in signaling behavior of tropical Rufous-capped Warblers (B. rufifrons). In the pre-breeding season, both sexes responded strongly to all conspecific intrusions, especially paired intrusions, by approaching the playback speakers and vocalizing. In the breeding season, males actively defended the territory alone whereas females rarely responded. Our results suggest that both sexes of Rufous-capped Warbler use vocal signals for shared territory defense, although the contributions of each sex to territory defense differ seasonally.