Long-Term Persistence of Song Dialects in the Mountain White-Crowned Sparrow

Abstract

This study examined the persistence of local song dialects of Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) at several locations in the Sierra Nevada Mountains of California. At two of these locations, where sparrows were numerous and occupied large contiguous habitat patches, song structure remained highly consistent over a 26-year period (1970-1996). Small but significant alterations in some aspects of the component syllables appeared to result from accumulation of slight copying errors. The frequency and duration of the introductory whistle changed little while the trill and complex syllables changed significantly. Dialects at these two locations were unaffected by extinction of syllables or invasion by foreign syllables. In contrast, songs recorded from two other areas (fragmented habitat and small populations) exhibited dramatic qualitative changes in overall structure and component syllables. These changes resulted both from loss of syllables and appearance of new syllables evidently introduced from nearby areas. These findings suggest that evolution of this culturally transmitted trait (song) proceeds more rapidly in smaller populations occupying structurally fragmented habitats than in larger populations occupying large contiguous habitat patches.