The Relation of Coloration in Mammals to Low Temperature

Abstract

It is well known that the color of certain mammals, such as the snowshoe hares ( Lepus ), collared lemmings ( Dicrostonyx ), weasels ( Mustela ) and Arctic foxes ( Alopex ) changes with the seasons, the animals becoming white in winter and brown in summer. The explanation usually advanced is that this seasonal difference in coloration renders the animals inconspicuous against the snows of winter and the brown background in summer and thus they avoid detection. Recently another interpretation has been advanced to account for these coloration changes. The following quotation taken from Hesse, Allee and Schmidt's ecological animal geography, Ed. 2, 1936, expresses the basic tenets of this concept. “The warm blooded animals of polar regions contrast … with … poikilothermic forms in their pale or pure white coloration.… The poikilothermic forms are almost all dark, and thus absorb the greatest amount of heat during the brief period of their activity. The white coloration of the homeotherms radiates less heat than the dark, and prevention of heat loss is evidently of greater importance than the absorption of the relatively small amounts of heat received from the sun.… Every means of heat conservation for homeothermic animals in polar regions is of importance, since they depend directly on heat of metabolism during the greater part of the year, and only secondarily on radiant heat from the sun.” In order to test the validity of the heat conservation concept the heat production of normally colored albino rats ( Rattus norvegiens ) was compared to those dyed black. Albino rats were used because of their uniform color and density of fur. Preliminary experiments comparing weasels in the brown summer and white winter pelage showed that there were marked seasonal differences in fur density that could modify the results. Acknowledgments .—Acknowledgment is made for aid and …