Radiometric Determination of Feather Insulation and Metabolism of Arctic Birds

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Abstract
Infrared thermograms of 4 species of arctic birds, the black-capped chickadee, gray jay, white-tailed ptarmigan and raven in environments of minus 7[degree] to minus 40[degree]C, were taken with a radiometer. Absolute feather temperatures were determined by relating a gray scale on the thermogram with densitometer readings. Thermograms of these birds showed the surface temperature of the feathers to be warmest in the eye-auricular region, the breast, and the upper side. The warm bill of the raven resulted from the respiratory heat exchange in the large nasal, subocular and lacrimal cavities. In addition, the vasculature of the eyelids appears to be greater in the ptarmigan and raven than the other birds. Feather temperature closely approached the ambient temperature as the weight and size of the bird increased. Insulation reached a maximum value at a temperature below the critical temperature. Thus, there was an overlap between maximal physical thermogenesis and onset of chemical thermogenetic responses to a cold stress. Core temperatures of the birds were more stable as their body weight increased. These data were used to formulate predictive equations for determining metabolic rates of these birds at various ambient temperatures.

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