This is BirdNote!
Vermont field naturalist and writer, Bryan Pfeiffer, writes today’s story:
It’s an aster in winter, sun through the clouds — a force of nature called the Yellow-rumped Warbler. Discover this songbird's buttery warmth, even when life outside seems to groan or crunch or crack in the cold.
By now most warblers have migrated south. But the Yellow-rumped Warbler, which birders affectionately call “butterbutt” is a lesson in adaptation.
In winter, when most of their kin are enjoying insects in the tropics, Yellow-rumps are finding food across parts of the West, the southern U.S. and north into New England. With insects in short supply, the Yellow-rump turns to fruit: juniper, viburnums, and mountain ash.
But this warbler’s greatest dietary feat is that it also eats the fruits of bayberry and wax myrtle — the raw materials of folksy candles. Digesting wax takes guts — literally. To do so, it appears that Yellow-rumps possess elevated levels of bile salts, which aid digestion of saturated fats.
The Yellow-rump’s gastrointestinal talents probably account for its ability to inhabit a winter range farther north than its relatives. Particularly along the Atlantic coast, [where wax myrtle and bayberry can be abundant] birders, in a day, might find butterbutts in the hundreds — abundance unlike any wintering warbler in North America.
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Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Calls of Yellow-rumped Warbler  recorded by M. Andersen; calls of Yellow-rumped Warbler [ 107591] recorded by D.S. Herr.
BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler.
Wind Nature Essentials #02 recorded by Gordon Hempton, of QuietPlanet.com
Written by Bryan Pfeiffer, and adapted from “The Winter Warbler.” Visit Bryan's blog at http://bryanpfeiffer.com/blog/.
Narrator: Michael Stein
Producer: John Kessler
Executive Producer: Chris Peterson