It’s another snowy day out on the Front Range and while I’m cooped up inside, I’m enjoying watching the birds flitting around my feeders. A couple minutes outside with no gloves on and my hands are starting to go numb, but these juncos and finches are clutching freezing metal with their little toes and hopping around in the snow with no problem. It makes you cold just to think about it, but even though these birds’ feet are pretty cold, they’re not getting cold feet.
Unlike us, birds have few nerves in their feet, so the cold doesn’t affect them as much as it does us. That’s why ducks and geese can swim around in icy water. Birds can fluff up their feathers and sit on their feet to warm them (similar to how you might stick your hands in your pockets or place them under your arms), and some birds that live in colder climates even have feathered legs, but birds also have an ingenious circulatory system called rete mirabile, meaning wonderful or miraculous net.
A bird’s veins (carrying blood back to the heart) and arteries (carrying blood out from the heart) are close together in its legs and feet, so close they intertwine. This allows warm blood from the heart to heat up the colder blood traveling back to the heart from the extremities. This heats up a bird’s legs and feet enough that they keep from freezing and keeps cold blood from getting back to the bird’s core, which would chill the bird. Because a bird’s feet are usually pretty small in comparison to the rest of the bird’s body, the amount of heat lost from a bird’s feet is also pretty small.
So you can put down the knitting needles; birds are doing just fine without little birdy booties.