Short Communications Heat Loss from Ducks’ Feet Immersed in Cold Water

The feet of birds are important in the regulation of core temperature (Kahl 1963, Steen and Steen 1965, Johansen and Millard 1973) and are particularly effective in heat transfer when birds are normoor hyperthennic (Steen and Steen 1965). Under natural conditions, they must also be sites of considerable heat loss when they are immersed in cold water or in contact with cold substrates (e.g., ice). However, the heat loss during cold stress can be substantially reduced by altering the pattern of blood flow to the feet (Grant and Bland 1931, Johansen and Millard 1973) and/or by transfer of heat from the arterial to the venous blood in vascular retes (Ederstrom and Brumleve 1964, Steen and Steen 1965). Nevertheless, since tissues in the feet of birds presumably are maintained at or above 0°C (Irving and Krog 1955), some heat must be lost from the feet. We expected that, at temperatures below the freezing point, additional heat would be required to keep the feet from freezing, and that this amount of heat would increase with decreasing temperature. We therefore used calorimetric measurements to determine the exact amount of heat lost from the feet of Mallards (Anus platyrhynchos) when their feet are immersed in fluids at low and subfreezing temperatures.