Foraging behavior by beaver (Castor canadensis): examining preferences for species, distance, and tree size.

Abstract

The purpose of this study was to investigate the foraging behavior and preference of the beaver (Castor canadensis). This behavior is an example of the herbivore-plant interactions. Foraging strategies of herbivores and plant diversity are thought to be the result of co-evolution. We surveyed one site on Douglas Lake at UMBS in Cheboygan County where a beaver lodge existed and where extensive foraging took place in the surrounding forest. In four 20 x 20 m plots as replicates, we surveyed a total of 228 trees. The variables recorded were tree species, distance from the lake, and diameter at gnawing height (approximately 0.3 m above ground), and fate of the tree (unattacked, gnawed, felled, or removed). We found that beavers are selective for tree species. They preferred bigtooth aspen (Populus grandidentata) and American beech (Fagus grandifolia), and they did not prefer red oak (Quercus rubra), red maple (Acer rubrum), sugar maple (Acer saccharum), paper birch (Betula papyrifera), and the white ash (Fraxinus americana). White pine (Pinus strobus), red pine (Pinus resinosa), moosewood (or striped maple, Acer pensylvanicum), and silver maple (Acer saccharinum) were omitted from the data analyses because fewer than five trees were encountered for each. There was no particular preference for trees at distances from the lake, and a size-distance regression proved no significance, either. However, we suspected a larger sample size would have accentuated the slight negative relationship between the size of foraged trees and distance from the lake. It was also found that beavers selectively foraged on both large trees (d > 22.1 cm) and small trees (d < 9.7 cm). Beavers do not remove large felled trees, but often remove small trees from the foraging sites. These preferences suggest that beavers as a species have evolved feeding strategies to improve their relative rates of survival and reproduction.