Sunday, October 13, 2013

Yellow-rumped (Myrtle) Warbler

I previously blogged about Myrtle and Audubon’s warblers and the dangers of lumping them in one species (the Yellow-rumped Warbler). Last week I banded the bird in this photo. Despite the buffy-yellowish sides of the throat, this is clearly a Myrtle Warbler. Note the line that continues from the back of the throat and continues half-way around the dark cheek patches. This line is lacking in an Audubon’s Warbler, which also lacks much of a supercilliary stripe. Thus Audubon’s Warblers (which also have a white eye ring) have a much more hooded appearance. The Myrtle Warbler breeds across northern Canada and some of the northern-most states in our country. The Audubon’s breeds in the Pacific Northwest and northern Rockies of both countries. Myrtle Warblers breed and are common migrants in Minnesota. Audubon’s Warblers are rare vagrants to our state.

One of these days Myrtle and Audubon’s warblers may once again be considered to be separate species. They only have a narrow band of hybridization in British Columbia and Alberta. This band is generally less than 200 kilometers, and genes from each race do not spread far from the area of hybridization. Away from this band, the two groups’ DNA differ “well below the average distance between species, but typical of some closely related species pairs” (Hunt and Flaspohler 1998). These ornithologists conclude that “further work on the complex may be appropriate."

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