Neighbor-stranger discrimination by song in a suboscine bird, the alder flycatcher, Empidonax alnorum

Abstract

Bird song and its functions have been studied extensively for more than 50 years, but almost entirely in oscine passerines. Few studies have investigated any aspect of song in suboscine passerines. This is significant because song development and the extent of individual variation in song differs greatly between these groups. Learning and auditory feedback play major roles in song development in all oscines studied, but apparently no part in song ontogeny in suboscines. The ability of territorial oscine males to discriminate between songs of neighbors and strangers has received considerable attention, but this phenomenon is virtually unstudied in suboscines. We tested whether a suboscine bird, the alder flycatcher (Empidonax alnorum), was able to discriminate between songs of neighbors and strangers despite limited individual variation in song. We performed playback experiments to measure responses of males to songs of neighbors and strangers broadcast from the territory boundary shared by the subject and the neighbor. Subjects responded more aggressively to songs of strangers than to songs of neighbors. These results further our understanding of the evolution of song and its functions in suboscines by demonstrating that, similar to their oscine relatives, they can discriminate between the songs of neighbors and strangers.