Hatching and the Establishment of Thermoregulation in the Wedge-Tailed Shearwater (Puffinus pacificus)

Abstract

Late-incubation unpipped eggs, pipped eggs, and hatchlings of the wedge-tailed shearwater (Puffinus pacificus) were exposed to constant ambient temperatures ($T_{a}'s$) between 28° and 38°C (eggs) or 15° and 43°C (hatchlings). Below 36° C (incubation temperature for shearwater eggs), oxygen consumption ($\dot{V}O_{2}$) and body temperature ($T_{b}$) of embryos varied directly with $T_{a}$, even with individuals in eggs with well-developed pip holes. Thus, shearwaters appear unable to initiate and sustain any effective cold-induced thermogenesis before hatching, even though access to oxygen appears to improve substantially during pipping. In contrast, hatchlings increased their $\dot{V}O_{2}$ by as much as 74% during cooling, with the maximum rate occurring at a $T_{a}$ of 25°C. The consequent increase in heat production served to maintain $T_{b}$ near 35°C at $T_{a}'s$ between 25° and 35° C, but hypothermia tended to develop below 25°C. Hatchlings increased pulmocutaneous evaporation at $T_{a}'s$ above 36...