BAKKEN, George S.*; WILLIAMS, Joseph B.; RICKLEFS, Robert E.; Indiana State University; Ohio State University; University of Missouri — St. Louis: Metabolic Response to Wind of Downy Chicks of Arctic-breding Shorebirds (Scolopacidae)

Wind is a significant factor in the thermoregulation of chicks of shorebirds on the arctic tundra. We investigated the effect of winds typical of near-surface conditions (0.1 – 3 m/s) on metabolic heat production, evaporative cooling, and thermal conductance of 1-3 week old downy scolopacid chicks (least sandpiper, Calidris minutilla; short-billed dowitcher, Limnodromus griseus hendersonii; whimbrel, Numenius phaeopus). Body mass ranged from 9 to 109 g. To accurately measure the interacting effects of air temperature and wind, we used two or more air temperatures between 15&deg and 30&degC that produced cold stress at all wind speeds, but allowed chicks to maintain normal body temperature (ca. 39&degC). Thermal conductance increased 30% – 50% as wind increased from 0.1 to 3 m/s. At similar mass, conductance is somewhat lower than that of 1-day old mallard ducklings, but higher than that 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 was best described by a function of standard operative temperature.