Body temperature (Tb) measurements after exposure to air temperatures (Tₐ) of 20 C or 27 C for 2 h in conjunction with metabolism measurements were used to describe the timing of and basis for developing temperature regulation in nestling swallows. As growth proceeds from hatching to 10 g there is a gradual increase in the Tb after exposure to low Tₐ. As growth continues beyond this point, the ability of nestlings to maintain Tb above Tₐ improves rapidly, such that nestlings weighing over 14 g are completely homeothermic when exposed to 20 C. Conductance (C, in cal [g⋅h⋅°C]⁻¹) decreases throughout growth following the equation: log C = −0.501 log m + log 6.902, where m = mass in grams. Conductance values and the relation of Tb to metabolism were used to predict the Tb after exposure to 20 C for 2 h, assuming the nestlings cooled passively. These calculations demonstrate that large changes in Tb − Tₐ can occur with growth even in the absence of active metabolic regulation. The major conclusions of this study are: (1) in bank swallows, mass is a better predictor of thermoregulatory ability than age; (2) conductance values are influenced mostly by increasing mass, whereas the developing plumage during the nestling period does not significantly retard heat loss; (3) apparent improvement in thermoregulation with growth in nestlings weighing less than 10 g is due to changes in passive resistance to cooling, not improvement in active metabolic regulation; and (4) active metabolic regulation develops rapidly as nestlings increase in mass above 10 g.


Originally published in Physiological Zoology 52: 340-353, 1979. http://www.journals.uchicago.edu/doi/abs/10.1086/636700


endothermy, birds, nestlings, bank swallows, Riparia riparia

Subject Categories

Bank swallow--Physiology


Poultry or Avian Science


University of Chicago

Publication Date


Rights Information

© 1979

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University of Chicago

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