Why do Calypte hummingbirds "sing" with both their tail and their syrinx? An apparent example of sexual sensory bias.
Courtship displays frequently include complex signals that females use to pick a mate. Male Costa's hummingbirds (Calypte costae) generate two acoustic signals during courtship: a vocal song produced close to a female and a dive-sound produced during a courtship dive. The song and dive-sound sound similar, and both were assumed to be produced vocally by the syrinx. Here, we show that they are not; whereas the song is produced by the syrinx, the dive-sound is produced by high-frequency fluttering of the outermost tail feathers. The Anna's hummingbird (Calypte anna), sister to the Costa's, also sings a vocal song and produces a dive-sound with the wings and outermost tail feathers that sounds similar to a portion of the song. The interspecific match in signal form between the two species is not as strong as the intraspecific match. Phylogenetic reconstruction indicates that the dive-sounds may have evolved first, suggesting that the song may have evolved to mimic the dive-sound. We propose the "sexual sensory bias" hypothesis as an explanation for the match in form between the song and the dive-sound within each species, in which we suggest that new sexual signals can arise in response to preexisting female preferences for older sexual signals.
Clark
Christopher J
CJ
Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, USA. christopher.clark@yale.edu
Feo
Teresa J
TJ
D000818:Animals; D001717:Birds / Q000145:classification / Q000502:physiology*; D005241:Feathers / Q000502:physiology; D005260:Female; D008297:Male; D010802:Phylogeny; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013623:Tail / Q000502:physiology*; D014828:Vocalization, Animal