How do ducks' feet stay warm in winter?

Counter-current heat exchange: a winter adaptation

Have you ever spotted a duck standing on a sheet of ice and wondered how they kept their feet from freezing?

Ducks are able to regulate the temperature of their feet through counter-current heat exchange. This process occurs in other species like whales and sea turtles too.

Picture a two-lane highway, where one stream of traffic is travelling towards the heart (venous blood) and in the other lane, traffic is travelling towards the feet (arterial blood). As these two streams of traffic pass side-by-side, they exchange heat.

When a duck’s feet are in contact with a cold surface, its body relies on counter-current heat exchange to lower the temperature of the blood destined for its feet. This process occurs in their legs, where arterial blood is cooled by venous blood, which in turn warms up a few degrees.

Counter-current heat exchange is so effective, that in the case of mallards just five per cent of their total body heat escapes through their feet.

Ducks are benefiting from the fact that the smaller the temperature difference between two objects (in this case, ice and feet), the more slowly heat is exchanged. This is effective even though they’re in direct contact with a cold surface.

Extra measures to stay warm in extreme cold

When ducks feel discomfort on really cold days, they’ll take extra measures to keep warm. If a bird is especially cold, it may alternately lift one foot and tuck it into its feathers to help conserve heat.

Another thing that you may see a duck do is tuck their bill into their feathers. This practice serves two purposes. First, it warms the bird’s bill. And second, by placing its bill under its feathers, a duck can draw in warmer air.

These adaptations help ducks navigate winter in Canada, so they can thrive through to spring. That’s important for their health and wetland health because ducks, geese and other migratory birds deliver valuable benefits to the environment.