, Volume 92, Issue 1, pp 1-10

Free-running circadian activity rhythms in free-living beaver (Castor canadensis )

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The members of a beaver family studied under natural conditions in SW Alberta, Canada (115 °03′ W, 51 °02′ N) displayed a free-running circadian rhythm of activity with a period length of about 27 hours in winter, at a time when they were living under ice and had no access to land (Fig. 1, A and C). In summer, the period length of their activity rhythm was close to 24 hours (Fig. 1, B).