Although there is a large body of literature dealing with the nature of geographic variation in the songs of birds, few studies have examined such variation across the entire range of species of suboscine birds. We measured time and frequency characteristics of songs of Alder Flycatchers (Empidonax alnorum) from six regions spanning almost the entire range of the species, from Alaska to Maine. Both univariate and multivariate analyses demonstrated significant differences in song characteristics among regions, and discriminant function analysis classified 69% of songs to the correct region. We found no relationship between geographic separation and magnitude of difference in songs among regions—songs of birds from some widely-separated regions were more similar than they were to songs of birds from neighboring regions. We argue that these regional differences have a genetic basis, but the pattern of variation does not appear to be consistent with a simple “isolation by distance” model. The variation may reflect differing adaptation to optimize acoustic transmission in varying habitats across the range. However, more detailed studies, including examination of genetic variation among populations, are required to test such suggestions rigorously.
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