Summer diet selection of snowshoe hares: a test of nutritional hypotheses

We examined summer diet selection by snowshoe hares in the southwestern Yukon, Canada, and attempted to explain how plant qualities such as nutritional content (protein, energy, fiber, water) and defensive compounds affect hare food choice. Male hares were placed in enclosures in natural vegetation areas dominated by shrubs and in both open and closed spruce forests. Each site contained a variety of herbaceous plant species. After 24 h, hares were sacrificed, their stomachs collected, and the contents removed and analyzed. Of the 30 plant species recorded in the enclosures only 10 were identified in the stomach contents of the hares. The summer diet is composed predominantly of five plant species; Lupinus arcticus, Salix spp. Shepherdia canadensis, Betula glandulosa and Festuca altaica. The selection of these species changes between sampling times. Protein, energy and water contents were highest in leaf tissues of most species early in the season, and most species had an increase in fiber through the summer. Protein content consistently explains the largest amount of variation in diet selection, although protein selection is modified by extremely high concentrations of defence compounds. It is likely that hares are not protein limited and are selecting for other plant characteristics correlated with protein content such as energy content. It is significant that hares continue to ingest heavily defended species (e.g. Shepherdia canadensis, B. glandulosa and L. arcticus) when many less defended plants are available to be eaten (e.g. F. altaica, Epilobium latifolium and Anemone parviflora). Our results support the idea that hares are selecting dietary items on the basis of energy content. No single plant species can satisfy all of the hares' nutritional requirements and the selection patterns may reflect the need to balance many conflicting plant qualities.