Saturday, April 18, 2015

Possible Myrtle x Audubon’s Warbler hybrid

During the last two days in Northfield, Minnesota, I banded my first Yellow-rumped Warblers of this spring. I always double-check to make sure the bird I am banding is not a western “Audubon’s,” instead of the expected eastern “Myrtle” race. See my previous blog about identifying these two races.

One of the four Yellow-rumped Warblers I captured this morning startled me. The throat, which I expected to be pure white, was definitely washed with a relatively intense yellow. Otherwise the bird sported typical Myrtle field marks—a white supercilliary stripe above the eye, and the lack of a white wing patch. I believe this bird is a hybrid between an Audubon’s and Myrtle warbler. Overall, the bird is quite similar to Sibley’s illustration of a hybrid in the most recent edition of his field guide.

I have banded hundreds (if not thousands) of Yellow-rumped Warblers. Over the years, I have encountered at least two typical Audubon’s Warblers in eastern South Dakota. They breed in the Black Hills of western South Dakota. Minnesota enjoys about a half-dozen Audubon’s Warbler sightings. Today’s bird, however, is my first record that I have suspected of being a hybrid. Sibley writes that, although hybridization is common, hybrids are infrequently reported away from the Canadian Rockies, where the two forms overlap.

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