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An Analysis of the Heat Budgets of the Eggs and Nest of the White-Crowned Sparrow, Zonotrichia leucophrys, in Relation to Parental Attentiveness

D. R. Webb and J. R. King
Physiological Zoology
Vol. 56, No. 4 (Oct., 1983), pp. 493-505
Stable URL: http://www.jstor.org/stable/30155872
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
An Analysis of the Heat Budgets of the Eggs and Nest of the White-Crowned Sparrow, Zonotrichia leucophrys, in Relation to Parental Attentiveness
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Abstract

To determine the effects of abiotic thermal stresses on the eggs of white-crowned sparrows in two localities, we developed a general model of heat exchange by eggs in open-form ("cup") nests. Major routes of heat exchange are convective cooling and solar radiant heating. Metabolic heat production by the embryo and evaporation of water from the egg shell are not thermally important in outdoor environments. Equilibrium egg temperatures (an equivalent environmental temperature including the effects of convection and solar radiation when the parent is not on the nest) ranged from 10 to 45 C and were often at levels that would impede development. At a subalpine locality, the equilibrium egg temperature was always so low as to prevent development. At a montane locality at lower latitude, equilibrium egg temperatures were usually moderate but sometimes so high as to be lethal. Actual egg temperatures were rarely at equilibrium because the incubating female behaviorally compensated for low temperatures. Two types of compensation occurred. The female exploited transients in the thermal environment by scheduling her trips off the nest for times of relatively moderate temperature, and she exploited transients resulting from biophysical properties of the eggs by adjusting the length of her trips so as to prevent the eggs from cooling to very low temperatures. Trip length was significantly correlated with equilibrium egg temperature, as was the time of the trip during the day.

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