To further conserve heat in cold weather, waterfowl reduce the volume of blood flowing to their feet by constricting blood vessels in their legs. Experiments have shown that waterfowl gradually reduce blood flow to their feet as the air temperature drops to 32 degrees Fahrenheit (the freezing point). When temperatures fall below freezing, however, waterfowl again increase blood flow to their feet to prevent tissue damage. The birds also protect their feet by drawing them into their flank feathers and close to their body. To further minimize exposure in bitter cold weather, waterfowl often stand on one leg at time, tucking the other leg into their body feathers to protect it from the elements.
In a similar but reverse manner, waterfowl can release excess body heat through their feet, primarily by standing or swimming in water that is cooler than the air. This capability helps waterfowl avoid heat stress on long, hot summer days. Where legs and feet are positioned on the bodies of waterfowl also influences how the birds interact with their environment. In dabbling ducks and geese, the legs are located near the middle of the body, providing the birds with good balance for standing and walking. This offers many advantages, including the ability to feed on dry land and in very shallow water, nest in upland habitats, and spring almost vertically into flight to escape predators.
The feet of diving ducks are located near the back of their body. This makes walking difficult, but is beneficial for diving and swimming. These adaptations allow diving ducks to frequent large bodies of water and feed by diving, often at considerable depths. Their excellent diving and swimming abilities also help them escape predators. The trade-off is that diving ducks can’t spring vertically into flight like dabbling ducks and must instead make a running start across the water to achieve flight speed.
A final activity where the feet of waterfowl play an important role is flight. All waterfowl use their feet as rudders while flying. And as all waterfowl hunters have seen, ducks and geese lower their feet and spread the webbing between their toes right before they land. This creates a little extra drag that helps the birds slow down. Conversely, when waterfowl want to achieve maximum flight speed and efficiency, they pull their feet into their flank feathers just like retractable landing gear on an airplane.
In most circumstances, webbed feet have been wonderful adaptations that assist waterfowl in exploiting the wetland habitats where they live. Millions of years of adaptation have helped ducks, geese, and other water birds truly put their best foot forward.