For the Birds Radio Program: The Winter Feather Report
Birds are bulking out, preparing for the winter ahead. So Laura begins a 3-part series on feathers. 3:24
This is the time of year when birds are coming into their maximum number of feathers. Notice those chickadees at your feeder. They’re in perfect plumage, their black caps setting white cheeks off to perfection, gray back and buffy side feathers all clean and new, fluffed out with thick down feathers. Juncoes, White-throated and Fox Sparrows—everyone’s in fine fettle right now. I used to think the expression “in fine fettle” was etymologically related to the expression “in fine feather,” but it turns out the two phrases are completely different. “In fine fettle” comes from the Middle English word fetlen, meaning “to shape.” Its use comes from metallurgy, referring to lining a furnace with loose sand or ore in preparation for pouring in molten metal. A furnace in fine fettle was in proper, sound condition, ready for anything. A bird in fine fettle is also ready for anything the natural world may send its way, at least in terms of weather. But unlike furnaces in fine fettle, birds needn’t worry about excessive heat. Their feathers protect them against the kind of cold that could crack some of those Middle English metal works right in two.
New feathers are bright in most species, but for a few, the newest feathers are the dullest. Brand new cardinal feather tips are drab brown. It takes months for these dull tips to wear off, so during early winter their feathers are both the warmest and the most camouflaged. By late winter when their hormones are kicking in, their tips will be worn off enough to help them attract a mate by exposing the brilliant red beneath. Of course, all winter the males are red, but they’re at their best after their feather tips wear off.
Feathers provide the finest insulation available in the natural world, and on a blustery November day, birds need all the insulation they can get, so to prepare, they grow extra feathers. House Sparrows trapped and killed in Michigan in July had about 3,100 feathers. House Sparrows caught in the same area in January and February had about 3,600 feathers, meaning they probably have more than 11 percent more feathers in winter than summer. Two related species may show a huge difference in the average number of feathers depending on their range. For example, the Blue Jay has fewer feathers than the Gray Jay. Gray Jays don’t weigh any more than Blue Jays, but are much bulkier thanks to their more dense layer of down feathers.
To maximize insulation, birds can control their outer feathers, called contour feathers. Every single feather we can see on a bird is connected to its own personal muscle cell. When birds are warm, they can flatten their feathers with bundles of depressor muscles, or fluff them out to keep them warm with erector muscles.
Up or down, feathers are bright and elegant, and November opens the season of richness and abundance for them, nature’s greatest contrivance.