Egg Temperatures and Parental Behavior during the Transition from Incubation to Brooding in the American White Pelican

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Abstract
I monitored incubation behavior and egg temperatures (Te) recorded with agar-filled eggs before and during hatching in American White Pelicans (Pelecanus erythrorhynchos) to determine if embryos were subject to more extreme temperature conditions at this critical period than at other stages of development. Before pipping, mean Te was 35.2.degree.C. It did not change significantly in the presence of a pipped egg or newly hatched young. Diurnal variations in Te were absent prior to hatching, despite a slight but significant correlation between Te and ambient temperature (Ta). A small drop in Te (about 2.degree.C) occurred in early morning at nests containing one newly hatched young. Te minima at these nests correlated significantly with Ta. Range and variance in Te increased with onset of pipping and again when the first young hatched. Increasingvariability in Te was associated with progressive changes in relevant incubation behaviors. Eggs exposed by the removal of foot webs at the onset of pipping were subject to cooling when the parent raised to preen or settled with an egg protruding from the nest. The embryos were exposed to greater temperature extremes during the pipped-egg stage than in other stages. By calling when cold, embryos in pipped eggs may influence parental behavior and hence their own thermal environment.