This is BirdNode. Vermont field naturalist and writer Brian Pfeiffer writes today's

story. It's an ester 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 rumps

gastrointestinal talents probably account for its ability to inhabit a winter

range farther north than its relatives. Particularly along the Atlantic coast,

birders in a day might find butterbutts in the hundreds, abundance unlike any

wintering warbler in North America. For bird note, I'm Michael Stein.