Aspects of seasonal energy expenditure in the beaver (Castor canadensis Kuhl) at the northern limit of its distribution

Abstract

The beaver (Castor canadensis Kuhl) is subjected to a seasonally fluctuating energy regime in the northern portion of its distribution. During the summer the animal has free access to an abundant food supply in the form of growing plant material, while the winter food supply is limited to a store of cached saplings. The summer and winter periods are 4 and 8 months long respectively.In the Mackenzie Delta. Northwest Territories, growth was found to be rapid in the summer and absent in the winter, A winter weight loss characterized immature animals. Fat was deposited in the autumn, maintained during the winter, and mobilized in the spring. Animals were lean during the summer. Thyroid gland weights were high in the summer and low in the winter. It was concluded from these data that metabolic energy expenditure is high during the summer and low during the winter. This annual pattern is an inherent property of northern beavers. The adaptive significance of the pattern. is believed to be that energy expenditure is attuned to environmental energy availability.