Friday, September 24, 2010

Winter Wren

On Tuesday I banded a Winter Wren.  This wren was once thought to range from Europe and Asia across North America.  In 2010, however, this changed.  The American Ornithologists' Union now recognizes two species in North America, in addition to a third species in the Old World. The American species are named the Winter and Pacific Wrens. Pacific Wrens are found in the Rocky Mountains from the Aleutian Islands south to the San Francisco region and, further inland (but still in the mountains) in Canada and Montana.  The Winter Wren is found east of the Rockies across boreal Canada and in the northern United States (northern Minnesota, Wisconsin, Michigan, New England, and the Appalachians).

David Sibley writes about the difficulties involved in identifying these two new species.  Telling them apart is very difficult, and best done by their call notes.  Even differentiating the call notes is challenging.  So why are these species recognized?  The DNA patterns of these two populations do not mingle and are consistent, even where the two forms overlap, for call and song types.  (For a detailed discussion of these wrens' genetics, follow this link.)  I guess fortunately for us Minnesotans, the Pacific Wren is very unlikely to occur here--see the maps posted by Sibley.  Birders along the front range of the Rockies, where both species migrate or winter, will probably not be sure which species they encounter.

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