Embryonic fine tuning of pipped egg temperature in the American white pelican

Abstract

Upon pipping of the first (a) egg, the second (b) egg of the American white pelican, Pelecanus erythrorhynchos, is sometimes exposed to lower and more variable temperatures. Poor temperature control may arise at this time because the parents lack information about the current temperature state of the b-egg. Once chilled, embryos exhibit a graded response to cooling, which may restore the embryo's communicative link with the parent and enhance egg temperature control. This possibility suggested the hypothesis that pipped eggs are maintained at warmer temperatures than unpipped eggs during the final stages of incubation. At the onset of pipping, pipped a-eggs were significantly warmer than unpipped b-eggs in the same nest. This difference was not due to egg size. At more advanced nests, where the older a-egg had already hatched, temperatures of b-eggs increased significantly after pipping. Embryonic heat production was not a confounding variable in either situation. Results support the interpretation that late-stage embryos are able to influence their own incubation temperature by communicating with their parents.