THE EFFECT OF NUTRITIONAL QUALITY ON FORAGE PREFERENCE BY BEAVERS

We investigated the effect of nutritional parameters on preference by beavers (Castor canadensis) for five forage species. Cafeteria style experiments demonstrated that preferences ranked in the following descending order: trembling aspen (Populus tremuloides), white water lily (Nymphaea odorata), raspberry (Rubus idaeus), speckled alder (Alnus rugosa) and red maple (Acer rubrum). We assessed forage quality by determining dry matter, energy, crude protein, sodium, fibre and lignin contents as well as the digestibility of dry matter, energy and protein. Mean retention times of the diets in the gut of the beaver were estimated using a solid marker added to the forage. The mean retention times of aspen, raspberry and water lily were significantly shorter than those of alder and maple. Forage preferences were not significantly correlated with any single nutritional parameter. A linear programming (LP) model was used to determine if several of the parameters, when examined simultaneously, could predict forage preference. The LP model, using energetic and digestive constraints, correctly predicted the ranking of four of the five forage species in the diet of the beaver. These data suggest that beavers, like other vertebrate herbivores, select a diet which maximizes long-term energy intake, subject to digestive limitations.