Songs of the Cocos Flycatcher: Vocal Behavior of a Suboscine on an Isolated Oceanic Island

The conservative song development of suboscine birds may make them better subjects than the song-learning oscines for studying the genetic evolution of vocal behaviors. We used the Cocos Flycatcher (Nesotriccus ridgwayi) from Cocos Island, about 500 km southwest of Costa Rica in the eastern Pacific Ocean, to test whether isolation in a depauperate avifauna has reduced song stereotypy. Males sang two song forms and females one form. Measures of both temporal and frequency parameters for the three song forms revealed that variability of songs within and among individuals was not different from that of either a close relative in species-rich South America or two distantly related Empidonax flycatchers in species-poor North America. Thus, the impoverished acoustic environment apparently has not markedly affected the song stereotypy of the Cocos Flycatcher. Singing behavior of the Cocos Flycatcher was unusual, however, in that the female initiated and concluded most singing interactions with her mate and sang about twice as many songs as did the male. The significance of this reversed singing role of the two sexes is unclear.