Metabolic response to wind of downy chicks of Arctic-breeding shorebirds (Scolopacidae)

Wind is a significant factor in the thermoregulation of chicks of shorebirds on the Arctic tundra. We investigated the effect of wind at speeds typical of near-surface conditions (0.1-3 ms(-1)) on metabolic heat production, evaporative cooling and thermal conductance of 1- to 3- week-old downy scolopacid chicks (least sandpiper Calidris minutilla; short-billed dowitcher Limnodromus griseus; whimbrel Numenius phaeopus). Body mass ranged from 9 to 109 g. To accurately measure the interacting effects of air temperature and wind speed, we used two or more air temperatures between 15 degrees and 30 degrees C that produced cold stress at all wind speeds, but allowed chicks to maintain normal body temperature (approximately 39 degrees C). Thermal conductance increased by 30-50% as wind speed increased from 0.1 to 3 ms(-1). Conductance in these chicks is somewhat lower than that of 1-day-old mallard ducklings of similar mass, but higher than values reported for downy capercaillie and Xantus' murrelet chicks, as well as for adult shorebirds. Evaporative water loss was substantial and increased with mass and air temperature. We developed a standard operative temperature scale for shorebird chicks. The ratio of evaporative cooling to heat production varied with wind speed and air temperature.