(Puffing up to keep warm!)
Last night it got colder than I thought…down to -15°F. This morning I got up before sunrise, bundled up and went outside to top off the feeders and put fresh suet out. Generally, I discard partially consumed suet cakes by wedging them in branches for squirrels to eat. Though wrapped up in several layers, only after 10 minutes I was very ready to get back inside.
(Yellow-rumped Warbler Range Map)
Perhaps it is merely my own paradoxical connotation of the word “warbler” when it comes to temperatures this cold – warblers mean spring. But I know the wintering range for the Yellow-rumped Warbler isn’t much further south and such records aren’t unusually rare for southern Wisconsin. However, last evening as I closed the garage door I couldn’t escape the thought of that little 12-gram wood warbler enduring the next 12 hours sleeping in such frigid temperatures. Where is it roosting?Just after sunrise, I could barely contain my excitement to see the warbler zip across the yard to the suet feeders…it survived the night. It seemed to me that its chip-notes were an acknowledgement of its own heartiness and perseverance…as if calling out “I’m still here!” Nibbling on fresh suet, it seemed right at home with the Black-capped Chickadees, Red-breasted Nuthatches and Dark-eyed Juncos (no less marvels by their individual survival merits).
How do they do it? How does a bird that can fit in the palm of my hand keep from freezing rock-solid through the night? I decided to refresh my understanding and checked a few sources, and here is one excerpt from the Sibley Guide to Bird Life and Behavior:
"Many feathers (down, semiplumes and after-shafts) have significant insulating properties. In fact, feathers provide better insulation than mammalian hair. By fluffing out its contour feathers, a bird creates air pockets between the feathers and the skin that help retain heat. When resting, a bird can tuck is head or other body parts with exposed skin into its feathers to conserve heat."
Of course, there is much more technical information regarding temperature regulation and metabolism, but that’s the gist of it. It also helps that the Yellow-rumped Warbler is a generalist when it comes to its diet and habitat requirements. From Cornell’s Birds of North America on-line:
"Among warblers, this species is one of the most ecologically generalized. Although it is confined largely to coniferous breeding habitat, individuals forage in a broad range of microhabitats and employ a variety of foraging techniques, from fly-catching to foliage-gleaning for insects. During the nonbreeding season, this warbler is found in almost any habitat and expands its diet to include a substantial amount of fruit. Its ability to digest the waxes in bayberries (Myrica spp.) make it unique among warblers, and allows populations to winter in coastal areas as far north as Nova Scotia."
After tomorrow we’re looking at a warming trend running through next week. Now that March is just around the corner, I think this Yellow-rumped Warbler may be in the clear.
Yellow-rumped Warbler image © 2006 Mike McDowell