Winter, Ducks, and Cold Feet

Lake Arrowhead, nestled at 5,200 feet in the San Bernardino Mountains, is home to a variety of waterfowl that migrate south to escape frigid winter conditions in their northern breeding grounds. Cornell Lab of Ornithology’s Merlin Bird app lists 19 different species of waterfowl that have been observed at Lake Arrowhead. Some of the more common winter ducks on the lake include common goldeneye, redhead, canvasback, ruddy duck, American widgeon, and ring-neck duck.

For anyone who has spent a winter up here by the lake, you’ll know we have our share of snow and freezing temperatures, but the weather is more hospitable here than a typical January day in northern Canada or Alaska. So even though these birds have come south for a respite from harsh winter conditions up north, they are still subject to some pretty cold winter temperatures.

Imagine being outside 24/7 during the winter months in these mountains.

How do these ducks stay warm? Birds are warm-blooded (same as mammals) and maintain a constant body temperature of about 107ᵒ F, which is significantly higher than a human.

The first line of defense against cold winter temperatures is the feathers­—especially down feathers—that cover a bird’s body. Down is particularly effective for insulation. That’s why it is used to fill winter jackets and cold-weather sleeping bags. The structure of a down feather is different from other feathers that cover the outer body. Unlike down, the body feathers have tiny hook-like structures called “barbules” that provide strength and rigidity. Since down lacks these barbules, it has a “fluffy” structure, which makes it ideal for trapping air. The trapped air, together with the fluffy feathers, helps keep body heat from escaping while preventing cold air from getting close to the skin.

While down effectively insulates the duck’s body, its feet are still exposed to low temperatures as it swims in cold water. This can potentially subject a bird to significant heat loss. So how do ducks avoid having cold feet? The short answer is, “They don’t!”

Having cold feet is just a way of life for ducks (and pretty much any bird that lives in a cold setting). In fact, these birds need to have cold feet if they are to withstand winter’s biting temperatures. It is critical for cold-weather species to avoid losing body heat, so they have evolved an adaptation that conserves body heat by minimizing how much is lost to the surrounding environment. It is part of the bird’s circulatory system and it is called a “counter-current heat exchanger.”

Here’s how it works. Arteries that carry warm blood from the body core are in close contact with

veins in the legs that carry cooler blood from the feet back to the body core. Heat from the arterial blood is transferred to the blood in the veins, warming it as it returns to the body core. In this way, body heat is “recycled” by warming the blood returning from the feet to the body core. The counter-current heat exchanger means warmer blood never reaches the feet, but without it, much more body heat would be lost to the environment.