Bioenergetic measurements were made on adult, lactating females, and growing juvenile pine voles. Adult pine voles showed a seasonal cycle in daily maintenance energy requirements. Winter was energetically the most expensive season. Requirements during the summer season were the lowest of all seasons. There was no significant difference in the daily energy requirements between adult male or female voles except during the summer season. Nesting material was found to be an important insulator asset which significantly depressed total daily energy requirements of adults. The period of lactation among female pine voles was energetically very demanding. The average lactating female and her litter required 47.5 percent more metabolizable energy than nonbreeding adult females of equivalent bodyweight. The net conversion of metabolized energy into tissue production during the period of lactation was extremely high among lactating female pine voles. Production efficiency was estimated to be 26.0 percent over 21 days of lactation. Production efficiency of lactating female pine voles was considerably higher than estimates derived for other vole species. Juvenile pine voles between the ages of 22-46 days had metabolizable energy requirements which were similar to those of an adult. Over the 24 days of postnatal development, the average juvenile pine vole metabolized 282 kcal of energy of which 25.8 kcal was deposited as tissue. The overall efficiency of production in juvenile voles was 9.2 percent which was considerably higher than estimates derived for other species of voles. A lignin analysis of stomach contents showed a distinct seasonal cycle in the digestibility of foods consumed by voles from the maintained and abandoned apple orchard. The highest digestibilities coincided with the maturation of the apple crop. The quantity of primary production available during the winter was lowest of all seasons. It was estimated that the amount of primary production available to pine voles during the winter season could support 994 nonreproducing adult voles per hectare in the maintained orchard and 147 nonreproducing adult voles per hectare in the abandoned apple orchard. / Master of Science