A 'Tail' of Two Signals: Acoustic Mating Displays in Anna's and Costa's Hummingbirds (Calypte anna; Calypte costae)
Abstract
The evolution of complex courtship displays is of central interest in animal behavior. Anna's and Costa’s hummingbirds (Calypte anna and C. costae) produce complex acoustic courtship signals mechanically with wing and tail feathers during dives, and vocally with their syrinx. Both the song and the dive-sounds of Anna’s are complex and multisyllabic whereas in Costa’s both signals are one phrase and monosyllabic. I first (chapter 1) test how similar the dive-sounds and songs are to one another within individual, then (chapter 2) characterize macrogeographic variation in Anna’s and Costa’s song, and lastly (chapter 3) characterize microgeographic variation in Anna’s song. First, I analyzed dive-sound and song covariation within individual. I audio-recorded dive-sounds and songs from 13 Anna’s and 14 Costa’s and measured spectral and temporal components of both courtship signals. I found between-individual variation in all components but little within-individual covariation between dive-sound and song, suggesting that the correspondence between song and dive-sounds is not maintained within individual.