Long-term changes in songs and song dialect boundaries of Puget Sound White-crowned Sparrows

Few studies have examined song variation in populations of birds over sufficiently long periods of time to demonstrate changes in the geographic distribution of song types. Baptista (1977) recorded songs of Puget Sound White-crowned Sparrows (Zonotrichia leucophrys pugetensis) over much of their range in 1970 and 1977, describing six song dialects on the basis of differences in the terminal trills of songs. We documented the distribution of song dialects in the northern part of the range of this subspecies in 1993 and 1994. The two most-widespread dialects have persisted, but the limits of their distributions have changed. One dialect with limited distribution in 1970 was not encountered. We describe two previously-undocumented dialects with limited distribution, and identify subdialects whose distribution seems to be related to barriers to dispersal. We have no reason to believe that changes observed are the result of selection for one song type over another.