“A bird’s bill is not insulated. Nor are its legs and feet. So all those vulnerability points tend to be smaller in species that winter in cold zones — scaled down as a result of the natural selection process across countless generations.”
Feathers are the first line of defense against weather, Mr. Sibley said in a recent conversation, and besides enabling flight, “they’re streamlining, waterproofing, windproofing, coloration — all those things.” And down feathers, the soft, fluffy kind closest to the bird’s body, he added, are “the most effective insulation known.”
Using tiny muscles where their feathers attach to skin, birds can raise and lower them, thickening the insulating layer around their bodies, he said, “like putting on an extra jacket or getting into a sleeping bag.”
Also thanks to feathers, a bird can tuck in its most vulnerable body parts, particularly overnight. Heads are turned so beaks can be buried into the shoulder-like scapular feathers atop a wing “to reduce heat loss and recycle warmth in the same way people do when breathing into cupped hands,” Mr. Dunne writes. By perching on one leg, the bird can pull the other up into safety, conserving more heat.
Another cold-defying strategy of birds is shivering on demand to raise their body heat — that’s what chickadees do to emerge from torpor.
Small birds lose about 10 percent of their body weight each night year-round while at rest…
— Margaret Roach, from “How Birds Survive Winter Cold” (NY Times, Jan 29 2025)
Photo of Sparrow taken at 6:45 am at Cove Island Park. 22° F, feels like 17° F. Feb 21, 2025. More photos from this morning’s walk can be found here.
