Birds maintain a fairly high body temperature (Tb) compared to most mammals. In order to maintain a high Tb birds must have a high metabolic rate. High daytime energy expenditures are decreased during the night by lowering Tb. In this experiment daily Tb in house sparrows (Passer domesticus) were determined by telemetry methods. Tb (n=6) showed a decrease of 3.00 C from daytime to night time. The average daytime Tb was 42.7 C and night time was 39.7 C. Oxygen consumption (VO2) was measured in an open flow metabolism system. Metabolic rate had a daytime to night time difference of 2.40 O2/g.hr. Thermal conductance (K) decreased from a daytime K of .23 (mL O2.hr)/C to nighttime K of .14 (mL O2/g.hr)/C. At a Tb of 42.7 C the night time energy expenditure would be 38.8 KJ. At 39.7, the average night time Tb for house sparrows (n=6) the energy expenditure is 36.0 KJ. Therefore a house sparrow saves 7% energy in maintaining circadian rhythms. Deeper depressions of Tb, known as torpor, may be energetically efficient, but costly in predation.
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Regas, Pericles P., "Circadian rhythms of body temperature and metabolic rate in the House Sparrow (Passer domesticus)" (1998). Honors Theses, 1963-2015. 653.