Foraging preferences of Castor canadensis: tree species, size, and location.

Abstract

Castor canadensis (beaver) is an excellent animal model for studying optimal foraging theories. The beaver attacks woody plants for both a source of food and building material for its dam and lodge. A tree that has been foraged by a beaver will have obvious gnawing marks or may be felled by the animal. Beavers are central-place foragers, thus transportation of the woody material back to a specific location may be energetically very costly. To best understand the successful foraging strategies of animals and the decisions they make to maximize energy, minimize time spent foraging, and the avoidance of predators, the foraging of the beaver was examined. The study was performed adjacent to an active beaver lodge located on Douglas Lake, Pellston, MI, USA. We were able to quantify trees that had been attacked by the beaver using area transects in a second growth hardwood forest on the shoreline of the lake. Within this area, beaver activity was depicted by measuring the distance of attacked trees from the water's edge, the diameter of these trees, and the species. Using this data, Chi-squared analysis showed the beaver had preference of the species attacked, preferring Populus grandidentata (bigtooth aspen). However, there was no statistical preference between trees located at closer distances to those farther from the shoreline. Also, the chi-squared analysis of size of trees foraged showed that beavers avoided the mid-sized trees. However, there was no correlation between diameter and distance of attacked trees. The focus of this study is to develop a better understanding of how beavers optimize their foraging habits.