Environmental Influences on Initiation and Maintenance of Hibernation in the Arctic Ground Squirrel, Citellus Undulatus

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Abstract
A controlled laboratory experiment was designed to investigate the ecological effects of temperature and photoperiod on patterns of hibernation in the arctic ground squirrel. Increased hibernation was clearly associated with regimes of decreasing photoperiod and constant temperature. Decreasing temperature and constant photoperiod had similar, though greater, effects. The combination of decreasing photoperiod and temperature, which constituted the best simulation of natural conditions, was associated with a hibernation time exceeding the sum of times in the two independent tests. Photoperiod seemed to have as great an influence on initiation of hibernation as did temperature, although the latter was more influential in maintaining hibernation. Statistical analysis clearly indicated that, under the conditions of this experiment, simulated natural photoperiod and temperature fluctuations served as external environmental timing cues to which arctic ground squirrels responded by adjusting their patterns of hibernation. It is suggested that the same mechanisms may operate in the field.