Distribution of wolf dens on migratory caribou ranges in the Northwest Territories, Canada

Abstract

Most wolves (Canis lupus) on migratory caribou (Rangifer tarandus) ranges in the Northwest Territories den near the tree line, the northern limit of tree growth. Sixty percent of the 209 dens that we located were within 50 km of the tree line, an area representing only 25% of the caribou range. Den density in the forest was significantly lower than expected if dens were randomly dispersed. Within the tundra zone wolves did not show any preference for denning near caribou calving grounds. Most wolves may den at the tree line because caribou are likely available for a greater proportion of the denning period than they would be elsewhere and because caribou are usually abundant near the tree line in September, when the nutritional demands of the pups are greatest. Within the tree-line zone, habitat characteristics appeared to affect the local distribution of dens because wolves preferred to den where the roots of trees and shrubs provided structural support for the tunnels. With most wolves denning at the tree line, density-dependent summer range expansion and contraction by caribou may provide a mechanism by which changing caribou densities could influence the growth rate of the wolf population.