ASSOCIATIONS OF SONG PROPERTIES WITH HABITATS FOR TERRITORIAL OSCINE BIRDS OF EASTERN NORTH-AMERICA

To investigate adaptations for long-range acoustic communication in birds, I analyzed associations between broad categories of habitats and properties of territorial songs for eastern North American oscines. From published recordings, I obtained three frequency properties (maximal, minimal, and dominant) and three temporal properties of songs (presence of sidebands, presence of buzzes, minimal period of repeated elements). Sidebands and buzzes indicated rapid amplitude modulation of a carrier frequency. Habitats occupied by territorial males were classified into six categories (broad-leaved or mixed forest, coniferous forest, parkland or forest edge, shrubland, grassland, and marshes). Frequencies in songs correlated strongly with body size, which varied among habitats. Analysis of covariance and phylogenetic regression, after controlling for body size, revealed an association of maximal but not dominant or minimal frequencies with habitat. In contrast, the temporal properties of song were all strongly associated with habitat, even within phylogenetic groupings. These results suggest that the temporal properties of songs of many oscines have evolved to reduce the effects of reverberation in forested habitats. Exceptional species might have retained features of song subject to degradation to permit listeners to judge distances to singers. In addition, adaptations for acoustic communication in different habitats might include differences in the perception of songs.