The birds also protect their feet by drawing them into their flank feathers and close to their body.
When temperatures fall below freezing, however, waterfowl again increase blood flow to their feet to prevent tissue damage. Experiments have shown that waterfowl gradually reduce blood flow to their feet as the air temperature drops to 32 degrees Fahrenheit (the freezing point). To further conserve heat in cold weather, waterfowl reduce the volume of blood flowing to their feet by constricting blood vessels in their legs. Thus, while the core body temperature of a duck standing on ice is near 100 degrees Fahrenheit, the temperature of the bird's feet may be just above freezing.
Consequently, very little of a duck's body heat is lost through its extremities. The warm arterial blood flowing to the feet is cooled by venous blood flowing back to the body where it is warmed again. Arteries supplying blood to the feet pass alongside the veins removing blood. The large, flat feet of waterfowl are natural radiators, so to minimize heat loss, the arteries and veins in the birds' legs work in tandem to retain heat. Ever wonder how a mallard can stand comfortably on ice? A unique heat-exchange system in the birds' legs known as counter-current circulation makes this possible. The legs and feet of waterfowl also play an important role in maintaining body temperature. Lastly, some waterfowl such as the Australian magpie goose and the Hawaiian goose (or nene) have half-webbed semipalmate feet, an adaptation that is useful for occasional swimming and walking on soft surfaces.
#SOMETHING WITH WEBBED FEET SERIES#
Coots have lobate feet, where the toes have a series of webbed lobes that open when the foot is pushed backwards-much like the base of a push pole used by duck hunters to traverse the marsh. Ducks and geese have palmate feet, where only the three front toes are webbed and the hind toe (called the hallux) is small and elevated.
Cormorants and boobies have totipalmate feet, where all four of the birds' toes are connected by webs. The most common difference is in the amount of webbing between the birds' toes. The feet of water birds are all structurally similar but vary among species. This provides a combination of lift and thrust, propelling the birds through the water with remarkable speed and efficiency. For example, researchers recently discovered that while swimming, waterfowl push both backward and downward with each stroke of their webbed feet. Features such as webbing of the feet arose over time as the birds adapted to make the most of their wetland environments. Of course, the legs and feet of waterfowl play a vital role in many other important activities, including locomotion (walking, swimming, and flying) and thermoregulation (maintaining body temperature). In summer, hormone levels in ducks decrease, and their feet and bills become drab in color again, which helps camouflage the birds while nesting and molting. Heavier adult mallards typically develop breeding plumage and display brightly colored feet earlier than younger, lighter birds, giving rise to the mistaken belief that "redlegs" are a different race or subpopulation of larger mallards.
The feet of both male and female mallards turn bright orange-almost red-in December and January as they go through courtship and pairing. In reality, the brightly colored feet and bills of mallards and other ducks are caused by changes in hormone levels during late fall and winter while the birds are pairing. Old-timers called these big, late-migrating mallards "redlegs." These mallards are also thought to be larger and hardier than mallards raised in southern parts of the species' range. Have you ever heard that you can tell where a mallard is from by the color of its feet? As the story goes, the legs and feet of northern mallards are redder than their southern cohorts because low temperatures in higher latitudes cause more blood to flow to the birds' extremities.
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