. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 164 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY Vol. 124 pointed out that Eriksson's failure to find dependence of meta- bolic rate on ambient temperature is not in line with studies on other hibernators in the active condition. It is also apparent that the ground squirrel does not show the same lack of seasonal variation in metabolic rate as reported by Irving et al. (1955) for the red squirrel. Butterworth (1958) has stated that the Arctic ground squirrel has two annual molts, although other northern ground squirrels h
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 164 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY Vol. 124 pointed out that Eriksson's failure to find dependence of meta- bolic rate on ambient temperature is not in line with studies on other hibernators in the active condition. It is also apparent that the ground squirrel does not show the same lack of seasonal variation in metabolic rate as reported by Irving et al. (1955) for the red squirrel. Butterworth (1958) has stated that the Arctic ground squirrel has two annual molts, although other northern ground squirrels have only one. This may explain the seasonal variation here shown, as Irving et al. 30 25- . 20 E o 10 0 WINTER 0 SUMMER. —i— •10 0 10 TEM? °C 20 30 Fig. 8. Average metabolic rate of Arctic ground squirrels in relation to ambient temperature. Winter and summer curves are shown. (1955) concluded that the seasonal variation shown by the red fox was due to better insulation of the winter pelage over the summer pelage, while that of the red squirrel might be due to little pelage insulation change. However, it appears that this reduction in metabolism of the winter group may rather be a reflection of: (a) lower body temperature, and (b) considerably reduced general activity. It may also be that endocrine factors are concerned, but 1 have no direct evidence on this point. Metabolic rate during hibernation at 6° ±2°C ranges from to ml 02/gm/hr, with an average of about ml gm/hr, which is clearly within the expected range. It thus. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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