Use of woody plants in construction of beaver dams in northern Ontario

Newly formed beaver dams were studied in the Chapleau Crown Game Preserve of northern Ontario to determine if beavers (Castor canadensis Kuhl) showed any preference in their choice of woody plants in building the darns. Application of Neu's utilization-availability technique showed that beavers exhibited a high preference for alder (Alnus spp., plant species not commonly used as food) stems with diameters of 1.5-3.5 cm and a lesser preference for food-tree stems with diameters of >4.5 cm, We maintain that beavers used large food-tree stems only because they became more accessible after dam construction. Since the alder stems available close to the water's edge accounted for most of the stems of the preferred size, 1.5-3.5 cm, we postulated that selection of woody stems by beavers for construction purposes was based on size rather than on species.