Sharing of Vocal Signals among Song Sparrows

Abstract

In the scrub habitat along the central California coast, Song Sparrows (Melospiza melodia) are sympatric with White-crowned Sparrows (Zonotrichia leucophrys). Songs of male White-crowned Sparrows exhibit dialects and it was previously thought that these might be initiated by a founder effect. This hypothesis could be tested weakly by looking for concordant dialect systems among several songbird species in the same region. Given the known pattern of song variation in White-crowned Sparrows, I asked if vocal variation in Song Sparrows matched that of White-crowned Sparrows. Seven Song Sparrows were recorded at each of four sites located within the boundaries of three dialect areas of White-crowned Sparrows. Repertoire size of the Song Sparrows ranged from 6-18 songs (median 10). The 22 kinds of trills and 50 kinds of notes most commonly sung by Song Sparrows were examined for similarities among individuals and samples. Vocal sharing was not concordant with the dialects of White-crowned Sparrows. Only one or two types of notes or trills varied geographically in accordance with dialect variation in White-crowned Sparrows. Nor was there strong evidence for dialects in Song Sparrows that were discordant with those of White-crowned Sparrows. The results did not support the colonization hypothesis for the origin of dialects.