BANTA, M.R.*; VAN SANT, M.J.; BAKKEN, G.S.; University of Northern Colorado; Indiana State University; Indiana State University : Evidence for metabolic substitution in swimming mallard (Anas platyrhychos) ducklings

Substitution is the energetic phenomenon by which endotherms use heat generated during an activity such as digestion or locomotion for thermoregulation. This heat would otherwise have to be generated de novo through shivering or non-shivering thermogenesis. Substitution is of considerable potential value for precocial chicks, as they may use a large proportion of their energy budget for thermoregulation and activity, reducing the amount of energy available for growth. Unlike mammals, birds appear to lack non-shivering thermogenesis. The same muscles are used for shivering thermogenesis and locomotion. While locomotion may increase convective heat loss somewhat, it is reasonable to expect that heat generated by locomotion would indeed substitute for thermogenesis. We tested this prediction with young (2-3 d) mallard ducklings (Anas plathrhynchos) swimming in a controlled environment. We selected this study species because surface swimming has been shown to be energetically expensive for ducklings, the leg muscles are the largest and best developed in the body and so account for most shivering thermogenesis, and the rate of heat loss to water is substantially greater than heat loss to air. Sixty ducklings swam on two consecutive days in a flow tank at three water velocities in one of three water temperatures. Body temperatures and metabolic rates were recorded while the ducklings were swimming. At temperatures below thermal neutrality, metabolism for locomotion and thermoregulation were not additive, suggesting that ducklings were substituting heat gained during swimming for thermoregulation.