BANTA, Marilyn*; LYNOTT, Aaron; HIGGENBOTHAM, Clay; VAN SANT, Matthew; BAKKEN, George; Northern Colorado University; Indiana State University; Indiana State University; Indiana State University; Indiana State University: Thermoregulation on the Air-Water Interface: Heat Loss from Swimming Mallard Ducklings

Ducklings of Mallards breeding on the pothole prairies of North America leave the nest within a day or two of hatching. They then forage for themselves, typically while swimming in cold (ca. 10^oC) water. Water effectively removes heat by conduction and convection, and thus foraging while swimming incurs heavy energetic costs. However, these costs have never been quantified, even though field studies find increased mortality associated with wetting and chilling. Therefore, we investigated thermoregulation in 3-4 day old mallard ducklings (Anas platyrhynchos swimming in a flow tank with water temperatures from 5^o to 30^oC and ambient air temperatures from 10^o to 40^oC. The down of most swimming ducklings was not significantly penetrated by water, and they were able to maintain body temperature T_b above 37^oC for 1 hour while swimming in 5^oC water at a 10^oC air temperature. Most heat was lost to the water, with overall conductance to water about twice that to the air. We used these data to define a standard operative temperature scale for swimming ducklings not exposed to significant solar radiation, e.g. during heavy overcast. In contrast, when a significant area of down became saturated when water temperature was below 20^oC, T_b fell from 40^oC to 30^oC within 10 to 15 minutes. Hypothermic ducklings were capable of coordinated swimming as long as T_b exceeded ca. 28-30 ^oC, and quickly recovered normal T_b when placed in a brooder at 30^oC.