Responses to High Temperature in Nestling Double-Crested and Pelagic Cormorants

Abstract

ADULT and nestling cormorants are often subject to overheating from insolation at the nest. Their generally dark plumage, exposed nest sites, and reradiation from surrounding rocks aggravate the thermal stress. Young nestlings must be shielded from the sun by their parents. Older nestlings and adults compensate for heat gain through behavioral adjust- ments and modulation of evaporative cooling by panting and gular flutter- ing. This study was undertaken to examine some of the responses to high temperature in nestlings of two species of cormorants, the Double-crested Cormorant, Phalacrocorax auritus, and the Pelagic Cormorant, P. pelagicus. The evaporative cooling responses in birds have been studied in some detail in recent years (see Bartholomew et al., 1962; Lasiewski et al., 1966; Bartholomew et al., 1968; Calder and Schmidt-Nielsen, 1968, for more detailed discussions), although much still remains to be learned