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Cultural Evolution of Puget Sound White-Crowned Sparrow Song Dialects

Authors


Douglas A. Nelson, Borror Laboratory of Bioacoustics, Department of EEO Biology, The Ohio State University, 300 Aronoff Laboratory, Columbus, OH 43210, USA. E-mail: nelson.228@osu.edu

Abstract

The songs of male Puget Sound white-crowned sparrows currently form about 12 dialects along the Pacific Northwest coast. In his survey of 1970, Baptista (Condor 1977; 79: 356–370) defined six of the dialects based on the song's terminal trill because most males at each locality shared the simple syllables (SSs) in this trill. The complex syllables (CSs) in the song's introduction varied among males at a locality, and were often shared among localities. From 1997 to 2004 we revisited nine of the sites Baptista studied to determine whether the SSs and CSs had changed over the 30-yr interval. Using Baptista's catalogs of SS and CS types as bases for comparison, we found that the relative proportions of CS types changed significantly more over time than did the proportions of SS types. These results suggest that SSs and CSs evolve independently. Observations were also made on the developmental mechanisms that either produce diversity or maintain uniformity in song phrases. In a survey of 670 field-recorded songs, unique improvizations occurred significantly more often in CSs than in SSs. In a laboratory experiment using hand-reared males and multiple song tutors, males were significantly more accurate in imitating SSs than CSs. In choosing their final song to keep from their overproduced repertoire, yearling males tended to retain the song type that matched the SSs in the song played back to them. We conclude by discussing how differences in the functions served by these two song phrases may have led to their different rates of cultural evolution.

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