A human conversation that doesn’t happen:

“Brrrrr, I’m freezing out here!”
“Remember, you can turn your body’s temperature requirements down—then you’ll be fine.”
“Oh, right, good idea. I forgot how easy it is to re-set my internal dial.”

A bird adaptation that does happen:

In cold weather, birds sometimes turn their internal heat requirements down—in Pennsylvania, mourning doves and turkey vultures regularly use that trick. The dialed-down state is called torpor. Torpor occurs when birds automatically slow their heart rates and breathing so they’ll require less energy to keep their bodies going. This really helps when the weather is challenging and food supplies are limited.

Archibald_Thorburn painting
The middle mallard in this 1935 watercolor and gouache painting by Archibald Thorburn is warming his right leg by tucking it up against his body.

Other birds cope with winter in these ingenious ways:

  • Similarly to your adding extra clothes to your body, in autumn birds grow extra feathers to prepare for winter. A goldfinch or chickadee goes from having over a thousand individual feathers to around 2,500 in the colder months.
  • Birds fluff themselves out to create many thousands of minuscule air pockets between their feathers. This trapped air holds in heat, in the same way the air inside a down jacket creates insulation.
  • Blood vessels on the outer edges of the legs and feet of ducks in icy waters constrict so that less heat escapes from them.
  • Ducks, herons, geese, hawks, and gulls will often tuck one leg up next to their bodies to warm it while they continue to stand on the other leg. Every so often, they switch legs.
  • Birds shiver. Shivering burns energy, and as with any fire, the burning creates heat.

Except for torpor, all of these adaptations require growth or muscle movement, which in turn require lots of food as internal fuel. In cold months, you can help your backyard birds with a well-maintained feeder. Black-oil sunflowers and suet are particularly good sources of energy.

If you make your own suet, be sure to use a solid fat. Liquid fat that gets on feathers can cause birds difficulties with flight, putting them at risk from predators.

Christine Du Bois – Buxbaum, Ph.D., Lansdowne Bird Town Coordinator of the Lansdowne Bird Town

“Archibald Thorburn winter landscape with mallard.” From Wikimedia Commons, public domain