Saturday, April 23, 2011

Yellow-rumped Warbler

Yellow-rumped Warblers tend to be our first spring warbler migrants. They are hardy little birds and regularly winter along the Atlantic Coast to Nova Scotia and the Great Lakes in the Midwest.  A few occasionally attempt to winter in southern Minnesota.  Yellow-rumps have been seen for about the last week, and we banded this bird on 22 April 2011

Yellow-rumped Warblers owe this hardiness to a host of adaptations. In a post on the MOU listserv (21 April 2011) Rick Hoyme wrote, "The Yellow-Rumps have the longest digestive track of any of our warblers which is required in order to be able to digest seeds and extract energy from them..." They are far less picky than other warblers about what they eat and readily consume unfamiliar prey items.   Hunt and Flaspohler write, in The Birds of North America Online, that this warbler has "special digestive features for digesting waxes and lipids, including retrograde reflux of intestinal contents to gizzard, elevated bile-salt concentration in gallbladder and intestine, and slow gastrointestinal transit of dietary lipids."  Furthermore, items that other birds might find indigestible pass through Yellow-rumped Warbler intestines at a slower rate than more delectable fare.

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