Temperature Regulation in Neonates of Shorebirds

Abstract

-In the laboratory we determined cooling rates, resting and peak metabolic rates, and minimal thermal conductances in neonates of nine North American and five European shorebird species, with neonatal body masses between 4 and 55 g. We measured the initial (T,) and final body temperature (T) of chicks during 30-min exposures to an ambient temperature (TJ) of 18?C. For each trial, the change in body temperature was converted to an index of homeothermy (H) by dividing the final temperature difference between the chick and surrounding air by the initial difference, such that H = (Tf T,)/(Ti Ta). The interspecific relation between H and body mass (M; grams) could be described by H = 0.073 + 0.464 log,o(M). Among neonates, the interspecific relationships of effective net peak metabolic rate (peak metabolic rate minus the evaporative heat loss) to body mass could be described by PMR,, (W ind-') = 0.0161M0922, of minimal dry thermal conductance (minimal thermal conductance minus the evaporative heat loss) by h,,, (W C-' ind-') = 0.0114M?359, and of the ratio between heat production and heat loss by PMR,/h,, = 1.412M_563. Thus, the higher degree of homeothermy in larger neonates could be explained by their more favorable ratio of heat production to heat loss. Peak metabolic rates of shorebird neonates were 1.9 times the resting metabolic rates in the zone of thermoneutrality. Rate of decrease in body temperature could be adequately simulated with a Newtonian cooling model that incorporated metabolic measurements corrected for evaporative heat loss. The degree of homeothermy of shorebird neonates appears to be related primarily to body mass. The occupation of cold, arctic regions during the breeding season by some species does not depend on adjustment of either minimal thermal conductance or thermogenic heat production by neonates, compared to other species that breed in more temperate climates. Received 31 October 1991, accepted