Resistance to Hunger in Birds

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Abstract
Survival time of 6 passerine spp. without food and in darkness was measured at constant temps. between40[degree] and +46[degree] C. In the English sparrow (Passer domesticus), survival is longest, 67.5 hrs., at 29[degree] C, and decreases 2 hrs. per degree to 10[degree] C, and 1/2 hr, per degree from 10[degree]-40[degree] C. Above 29[degree] C, survival time decreases 4 hrs. per degree. From19[degree] to +35[degree] C, heavier birds live longer because the extra wt. is fat. The longer survival of oo over oo is due to their greater wt. At 34[degree] C, total wt. loss at death averages 36% of the initial wt., but at32[degree] and +43[degree] C, the loss is only 5% and 6%, respectively. The hourly rate of wt. loss varies inversely save that the minimum rate comes at 29[degree] C. Max. utilization of fat occurs only between 21[degree] and 35[degree] C: at lower temps. death is due to inability to maintain the greatly increased rate of heat production; at higher temps. death is due to inability to maintain a sufficiently increased rate of water evaporation. Differences between spp. and between individuals of one sp. in survival time is due to differences in relative amt. of fat stored in their bodies and the rate at which it is metabolized. Adjustments in behavior may partly compensate for deficiences in physiol, vigor and modify the controlling role of temp. and hunger on distribution. migration, and abundance .

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