USE OF WOODY-PLANTS IN CONSTRUCTION OF BEAVER DAMS IN NORTHERN ONTARIO

Newly formed beaver dams were studied in the Chapleau Crown Game Prese rve of northern Ontario to determine if beavers (Castor canadensis Kuh l) showed any preference in their choice of woody plants in building t he darns. Application of Neu's utilization-availability technique show ed that beavers exhibited a high preference for alder (Alnus spp., pla nt 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 t hey became more accessible after dam construction. Since the alder ste ms 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 wo ody stems by beavers for construction purposes was based on size rathe r than on species.