The thermal regime of eggs during laying and incubation in Greater Snow Geese

Dummy eggs were added to naturally incubated clutches of Greater Snow Geese (Chen caerulescens atlantica), an arctic-nesting species, in order to eval uate egg temperature during laying and incubation, and factors influencing egg cooling rate during female recesses. As laying progressed, both nest at tentiveness by females and egg temperature progressively increased. Althoug h the time spent at nest after laying the penultimate egg was relatively hi gh (69% vs. 91% during incubation), mean egg temperature was still 5.7 degr ees C lower than during the early incubation period. This suggests that lit tle embryonic development began before clutch completion. Thereafter, egg t emperature averaged 37.1 +/- 0.1 degrees C during periods where females wer e present, a value that decreased only slightly when incubation recesses ar e included (36.8 degrees C). This is a high temperature in comparison to ot her arctic-nesting geese. A modest increase (1.7 degrees C) in mean egg tem perature was observed as incubation progressed, but egg temperature was not influenced by clutch size or by the laying date of the first egg. During r ecesses lasting 24.7 +/- 1.3 min on average, egg temperature dropped by 2.8 +/- 0.3 degrees C, at an instantaneous rate of 0.23 +/- 0.02 degrees C hr( -1)degrees C-1. Cooling rates increased under windy conditions and decrease d with high solar radiation, but were little affected by air temperature.