Divergent Sexual Responses to Different Categories of Foreign Courtship Songs in Female Brown-Headed Cowbirds (Molothrus Ater)

Abstract

Abstract Female songbirds generally have an innate ability to distinguish between con-specific and heterospecific song, and may learn to discriminate among variants of conspecific song. By observing female copulation-solicitation displays elicited by playback of perched songs and flight whistles from distant (>2,000 km) widespread populations, we assessed the extent to which responses of female Brown-headed Cowbirds (Molothrus ater) to the two categories of male courtship song depend on experience. We hypothesized that female responsiveness to flight whistles is more dependent on experience than their responsiveness to perched song, because, though both perched songs and flight whistles vary spatially, perched songs always conform to strict species-specific structural and syntactic rules. Flight whistles, in contrast, are so variable that some types may not be recognizable as conspecific vocalizations to birds that have never experienced them. The species-wide structural similarities of perched songs make it possible for females to have innate responsiveness to these songs, as shown by isolate-reared females. In contrast, isolate-reared females do not respond to flight whistles. In the present study, females readily responded to foreign perched-song types, but showed as little response to foreign flight whistles as they did to heterospecific control songs. A previous study had shown that the same females were highly responsive to the local flight whistle. Thus, in accord with our hypothesis, females must have direct experience with a flight-whistle type to become responsive to it, but will respond to any unfamiliar perched-song type. Our findings for females are concordant with results on variation in the role experience plays in development of male production of songs from these two categories.