Behavioural thermoregulation in wintering black ducks: roosting and resting

Abstract

Black ducks (Anas rubripes) wintering near Ottawa, Canada, used a variety of behaviours to reduce their energy costs. The roost site that they occupied provided greater protection from wind than the feeding site, with the consequent reduction in forced convective heat loss. Time spent at the feeding site (i.e., away from the roost) varied with temperature such that ducks maximized their time at the roost on the coldest days. This relationship was facilitated by the ducks' food supply (cracked corn replenished daily), which precluded extending foraging time to increase food intake in cold weather. At the roost ducks huddled in colder weather and adopted postures that reduced both the nonfeathered area exposed to the air and also the surface to volume ratio. The ducks preferentially faced toward the sun and into the wind, but when these were in opposite directions they faced the sun only when wind speed was low.