Response to cold in the blue fox and raccoon dog as evaluated by metabolism, heart rate and muscular shivering: a re-evaluation.

Oxygen consumption (ml kg-0.75/min) in relation to ambient air temperature at or below the lower critical temperature (Tlc) of the winter-furred raccoon dog (+10 degrees C) and the blue fox (-6 degrees C) is described by the equations y = 14.8-0.28x and y = 7.5-0.20x, respectively. Muscular shivering activity (integrated EMG) of both species increased below thermoneutrality parallel with increasing oxygen uptake and heart rate. Seasonal changes in measured metabolic parameters were evident for both species. The results suggest that the overall body insulation or the metabolic response to cold are not essentially worse in the raccoon dog as compared with the blue fox. It is concluded that earlier speculations of surprisingly wide thermoneutral zone and very low Tlc of the Arctic fox are not evident for the blue fox.