Pictured are ducks on the Little Schuylkill River in Tamaqua this evening (Wednesday, February 18, 2015).
According to AskANaturalist.com: Ducks, as well as many other birds, have a counter-current heat exchange system between the arteries and veins in their legs. Warm arterial blood flowing to the feet passes close to cold venous blood returning from the feet. The arterial blood warms up the venous blood, dropping in temperature as it does so. This means that the blood that flows through the feet is relatively cool. This keeps the feet supplied with just enough blood to provide tissues with food and oxygen, and just warm enough to avoid frostbite. But by limiting the temperature difference between the feet and the ice, heat loss is greatly reduced. Scientists who measured it calculated that Mallards lost only about 5% of their body heat through their feet at 32 F. To put this in perspective, the rest of the duck is covered with feathers and in contact only with air, not ice, but because the body is relatively hot, 95% of the heat loss is from the head and body. Meanwhile, the cool feet sit on ice and give up very little heat.