Long-term persistence of song dialects in the Mountain White-crowned Sparrow

This study examined the persistence of local song dialects of Mountain Whit e crowned Sparrows (Zonotrichia leucophrys oriantha) at several locations i n the Sierra Nevada Mountains of California. At two of these locations, whe re sparrows were numerous and occupied large contiguous habitat patches, so ng structure remained highly consistent over a 26-year period (1970-1996). Small but significant alterations in some aspects of the component syllable s appeared to result from accumulation of slight copying errors. The freque ncy and duration of the introductory whistle changed little while the trill and complex syllables changed significantly. Dialects at these two locatio ns were unaffected by extinction of syllables or invasion by foreign syllab les. In contrast, songs recorded from two other areas (fragmented habitat a nd small populations) exhibited dramatic qualitative changes in overall str ucture and component syllables. These changes resulted both from loss of sy llables and appearance of new syllables evidently introduced from nearby ar eas. These findings suggest that evolution of this culturally transmitted t rait (song) proceeds more rapidly in smaller populations occupying structur ally fragmented habitats than in larger populations occupying large contigu ous habitat patches.