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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 2, June 2011 
the uniformity in first category singing among 
wood-warblers in eastern North America 
(Kroodsma et al. 1984, Byers 1996). Western 
North America, especially southwestern Oregon 
and northern California, has greater topographic 
diversity contributing to a fragmented landscape. 
Geography has an important role in the production 
and maintenance of song variants. Ridges exceed¬ 
ing 1,000-1,200 m in elevation separated the most 
distinct song forms. 
Fire also has an important role in the age and 
distribution of the mosaic of plant communities in 
the region (Agee 1993, Taylor and Skinner 1998), 
contributing to a fragmented landscape within 
watersheds. Stand-replacing fires are likely an 
important factor contributing to periodic isolation 
of populations and diversity of variants at this 
finer scale. 
ACKNOWLEDGMENTS 
We thank Greg Jones, Sean Curry, and Sean Mohren for 
assistance with the Geographic Information System. We 
also thank two anonymous reviewers for their helpful 
comments. 
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