Vocal regulation of temperature by avian embryos: a laboratory study with pipped eggs of the American white pelican

Abstract

When exposed to temperatures above or below normal mean incubation temperature, embryonic American white pelicans, Pelecanus erythrorhynchos, at the pipped egg stage called quickly and strongly in a graded fashion, then soon stopped calling when temperatures were returned to normal. The ability of pelican embryos to regulate their own body temperature by calling was examined by subjecting pipped eggs to an incubation temperature that was either above (50°C) or below (20°C) normal in a surrogate incubation apparatus that automatically returned incubation temperature to near-normal levels for a brief 4-min period whenever an experimental embryo called in response to heating or cooling. Under these conditions, embryonic temperatures initially drifted about 2°C from normal, then stabilized until the end of a 2-h experimental period. When a return to normal incubation temperature was controlled by calls of an embryo held in another room (yolked control), body temperature drifted erratically, and tended towards ambient, indicating that temperature regulation could not be achieved simply by random calling. Results show that late-stage pelican embryos are capable of vocal regulation of temperature provided a parent or surrogate responds appropriately to the embryo's calls. Vocal regulation of embryonic temperature by calling to cooperative parents is potentially operative in a wide range of precocial and some altricial species of birds.