Light alteration caused by snow and its importance to subnivean rodents

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Abstract
Silicon photocells placed in three habitats before snowfall revealed that light levels in the subnivean environment are inversely related to thickness of snow cover. Under 15 cm of snow in the fall, detectable light was sharply reduced. Under midwinter snow depths of 30 to 50 cm no light was detectable by the photocells used and color temperature readings showed greatest penetration to ground level in the red end of the visible spectrum. Sexual maturation of laboratory females of Clethrionomys gapperi was stimulated by white and blue radiation and increased daylength during late winter. Red light was not stimulatory, even over a 16-h day. As in other mammalian species, male voles did not appear to be as strongly photosensitive as females. Captive voles, given a choice of lights of different wavelength and total darkness, exhibited light-avoidance. Thus, the physiological and behavioral reactions of voles to the modified subnivean light regime ensure that subnivean winter breeding does not occur in this species. Factors controlling maturation of microtines that do breed under snow ought to be investigated.

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