Selection of natal dens by the swift fox (Vulpes velox) on the Canadian prairies

Abstract

The location and physical characteristics of 32 occupied swift fox (Vulpes velox) natal/rearing dens and 33 unoccupied sites in southeastern Alberta and southwestern Saskatchewan, Canada, were compared in 1991 and 1992. Comparisons between occupied and unoccupied sites were restricted to eight habitat variables that described the orientation of each den entrance, mean height of old and new grass, number of holes in each den complex, den position and slope (i.e., incline of the land) in relation to hills, and distance to the nearest roadway and water source. Two-sample t tests and Mann-Whitney U tests indicated that occupied sites were located on the tops of hills, close to roads, and in places where old grass was significantly higher than at unoccupied sites. Den entrance angles did not differ between occupied and unoccupied sites. A stepwise discriminant function analysis identified five potential discriminators of occupied and unoccupied sites (i.e., position on a hill, height of new grass, distance to water, distance to roads, and slope). Den position was the variable that discriminated most strongly between occupied and unoccupied sites. Occupied sites were located predominantly on the tops of hills. The quadratic discriminant function had an overall classification success of 83.1%. Based on the five habitat variables, the discriminant function model correctly classified 28 of the 32 occupied sites as being occupied (87.5%) and 26 of the 33 unoccupied sites as being unoccupied (78.8%). The habitat variables identified by the discriminant function model may be a useful tool for selecting and modifying release-site characteristics and creating more realistic live-rearing facilities.