Metabolic response to air temperature and wind in day-old mallards and a standard operative temperature scale

Most duckling mortality occurs during the week following hatching and is of ten associated with cold, windy, wet weather and scattering of the brood. W e estimated the thermoregulatory demands imposed by cold, windy weather on isolated 1-d-old mallard (Anas platyrhynchos) ducklings resting in cover. W e measured O-2 consumption and evaporative water loss at air temperatures f rom 5 degrees to 25 degrees C and wind speeds of 0.1, 0.2, 0.5, and 1.0 mis . Metabolic heat production increased as wind increased or temperature decr eased but was less sensitive to wind than that of either adult passerines o r small mammals. Evaporative heat loss ranged from 5% to 17% of heat produc tion. Evaporative heal loss and the ratio of evaporative heat loss to metab olic heat production was significantly lower in rest phase. These data were used to define a standard operative temperature (T-es) scale for night or heavy overcast conditions. An increase of wind speed from 0.1 to 1 mis decr eased T-es by 3 degrees-5 degrees C.