Development of Temperature Regulation in Shorebirds

Abstract

We studied the influence of body size on the development of temperature regulation in chicks of 10 North American and five European shorebird species belonging to the families Charadriidae and Scolopacidae. Neonatal body mass ranged between 4 and 55 g, and asymptotic body mass ranged between 20 and 650 g. We measured the change in body temperature of chicks individually exposed for 30 min to ambient temperatures of 2°, 10°, and 18°C. An index of homeothermy for each species at each ambient temperature increased as a linear function of the logarithm of body mass. Before achieving homeothermy at 18°C, chicks of small species almost tripled their body mass from hatching, whereas chicks of the largest species increased their body mass by only 10%. In the five European species we studied the development of resting and peak metabolic rate, and minimal thermal conductance, as a function of body mass. The development of homeothermy resulted mainly from a strong increase in the maximum mass-specific heatproduction due to thermogenesis (peak metabolic rate minus resting metabolic rate in the thermoneutral zone). The latter phenomenon is linked with a parallel reduction of the relative growth rate of the chick. These results are consistent with the hypothesis of Ricklefs (1979), who suggested that well-developed muscle function is incompatible with a high relative growth rate.