DEVELOPMENT AND USE OF TWO SONG FORMS BY THE EASTERN PHOEBE

Vocal development among oscines typically involves some form of vocal imitation, with young birds learning the songs of adult conspecifics or heterospecifics during early life (e.g., Slater 1983). In the field, the consequences of this vocal learning are readily apparent in the form of local song traditions (Mundinger 1982) or interspecific mimicry (Baylis 1982). In the laboratory, juvenile oscines denied experience with conspecific song typically develop very abnormal songs or else learn the songs of other species (Kroodsma 1982). Vocal development may be very different in the more “primitive” passerine suborder, the suboscines. In a study of the Alder Flycatcher (Empidonax alnorum) and Willow Flycatcher (Empidonax traillil), I could find no difference between the songs of wild birds and the songs of males or testosterone-treated females that were hand-reared in the laboratory from seven to ten days of age and denied access to conspecific song models (Kroodsma 1984). Vocal learning appears to play a negligible role in song development in these two Empidonax species. Such an interpretation is consistent with the relative absence of geographic vocal variation found in this genus (Stein 1963, Payne and Budde 1979, Johnson 1980). Together with morphological characters such as sperm structure, stapes structure, and syrinx complexity (e.g., Feduccia 1980), the mode of vocal development may distinguish the oscines from the suboscines. However, more data on vocal ontogeny are needed from other suboscines before such a generalization can be accepted confidently. I therefore initiated a study of vocal development in the Eastern Phoebe (Sayornis phoebe), a species closely related to the Empidonax complex (W. E. Lanyon, unpubl. data). Here I report that male and female laboratory-reared phoebes not only develop the two song forms characteristic of the species (Smith 1977) but that they also use them in typical wild-type fashion.