Sex-specific responses to simulated territorial intrusions provide evidence for relaxed selection pressure on female song in Orchard Orioles

Abstract

Female song has been significantly understudied compared with male song, and our understanding of how this elaborate signal trait may function has been limited as a result. Reconstruction of ancestral singing behaviors indicate that Orchard Orioles ( Icterus spurius ) have reduced female song compared with tropical ancestors. In this study, we found that male and female orioles on their breeding territories responded more strongly by all metrics to male song playback than to female song playback. Given the high degree of qualitative variation in female song and the reduced response to female playback, our results suggest that female song in Orchard Orioles may be under relaxed selection pressure. Sexual dimorphism in the complexity and frequency of songs in many lineages likely evolved as a result of a reduction or loss of female song. However, little research has investigated the functional significance of these reduced or infrequent female songs. More research is required to investigate the specific selection pressures that may be acting on female singing behavior in songbirds.

Keywords

• bird song
• female song
• icterus spurius
• orchard oriole
• relaxed selection pressure
• sexual dimorphism
• song playback
• songbird vocalizations