Dynamics of Incubation in Mountain White-Crowned Sparrows

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Abstract
The egg temperature (Tegg) of mountain white-crowned sparrows (Z. leucophrys oriantha) was measured throughout incubation and under natural variations in environmental conditions at high altitude. Information on Tegg, air temperature (Ta), nest placement and attentiveness patterns was integrated in order to elucidate adaptive forms of incubation behavior. Despite wide daily variations in ambient conditions, incubating females were able to maintain mean Tegg between 34 and 38.degree. C. Large oscillations in Tegg (17.8-43.0.degree. C) occurred when females were foraging, especially during early morning and late afternoon when Ta were low. Apparently low and fluctuating temperatures were not detrimental to embryo development. High Tegg did not occur because females prevented exposure of eggs to solar heating by remaining on the nest during critical periods. Mean Tegg was significantly higher in ground than in aerial nests. Habitat availability seemed to be of major importance for selection of nest height. Orientation of nests with respect to the vegetational mass in which they were built was non-random and was probably related to prevailing winds or to sun exposure.