Fluffy Feathers and Frigid Feet

You’ve probably seen birds fluff their feathers in winter.

The fluffy feathers form little puff pockets of air warmed by the birds’ bodies. But… have you ever seen a bird with feathered feet?

In the past few weeks, I’ve watched geese stand immobile for thirty minutes or more on ice and in shallow, frigid water. They seem unconcerned about freezing their feet. Turkey vultures poop on their feet to cool them off in summer. Is it possible, I wondered, that the geese are dropping little toe warmers, and I never noticed?

I reviewed hours of video featuring geese on ice. Nope. Nary a plop.

So, how do these birds function with frigid feet? First, there’s not much soft tissue in a goosefoot, so it doesn’t need much warmth to operate. Also, muscles controlling the foot are located high up in the leg. They push and pull the foot using long, tough tendons. Finally, geese, ducks, and swans have somewhat intertwined arteries and veins in their legs. That means the warm arterial blood flowing down the leg gives much of its heat to the cold venous blood traveling up from the foot. The foot receives blood that’s just warm enough to prevent damage.

Ornithologists call this process a counter-current heat exchange. And it turns out that warming the feet to just above the temperature of whatever the bird is standing on—or swimming in—reduces the bird’s overall heat loss. That’s a win for winter survival.

So, a waterfowl’s feet don’t need much warmth to function, and the heat exchange helps maintain that minimum temperature. But sometimes, heat exchange is not enough. That’s when you’ll see a goose or a duck standing on one foot—the other tucked under the bird’s insulating feathers.

Not all birds benefit from heat exchange anatomy. But most birds’ feet contain little fluid and their circulation is fast, so blood doesn’t stay in the feet long enough to freeze. And in winter, birds of a feather flock together… for warmth.

Here’s a quick look at a Red-bellied Woodpecker fluffing his feathers, followed by a video of several birds on ice. One even looks like he’s skating!

Does the Great Blue Heron have a built-in heat exchanger? I couldn’t find the answer. Herons are famous for their near-motionless prey stalking. But I’ve never seen one dilly-dallying on the ice. Maybe herons don’t care to tiptoe on popsicle toes.

If you’d like to read more about birds’ feet in winter, here are two of my sources for this blog post: Cornell’s All About Birds has a great overview. Ask a Naturalist explains the science in more detail.

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