Influence of Daylength on Activity of the Varying Lemming

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Abstract
The importance of lemmings in the arctic and subarctic regions has long been recognized, but there is little known about their ecology. The cause of cyclic populations in these animals remains unknown. In all of the studies so far recorded, the die-off has been in the winter or early spring following a population peak. At this time (in late winter) the length of daylight begins to increase, and it has been postulated that the increased light stimulates most mammals into sexual activity (Christian, 1950). This has not been demonstrated in the varying lemming, and furthermore, these animals are reproductively active at all periods of the year (Degerbøl and Møhl-Hansen, 1943; Manning, 1954; Ross, 1835; Sutton and Hamilton, 1932).