Multiple Scale Den Site Selection by Swift Foxes, Vulpes velox, in Southeastern Colorado

Abstract

Predation by Coyotes (Canis latrans) is a major source of mortality in Swift Fox (Vulpes velox) populations. Year-round den use by Swift Foxes is likely to be a predator avoidance strategy. Due to the importance of denning to Swift Fox ecology, we recorded den site selection of Swift Foxes in southeastern Colorado. Den site selection was recorded at two scales: microhabitat characteristics at the den and den placement within the home range. The number of den entrances, height and width of each entrance, aspect, hill position, slope, percent rock in soil, vegetative cover, and horizontal foliar density of 42 Swift Fox dens were examined during December 1999 – April 2000. This was compared to the same microhabitat characteristics at 42 random sites within Swift Fox home ranges to determine if Swift Foxes were using site characteristics according to their availability. Our results indicated that Swift Foxes were not highly selective of den sites based on the microhabitat characteristics evaluated in this study, although Swift Foxes selected areas of intermediate rock percentages. In addition, Swift Foxes were radio-tracked throughout the sample period and the location and frequency of use of known dens were recorded. Within the core area of home ranges, Swift Foxes used more dens (mean = 3.51 ± 1.70 (SD)), and had a higher frequency of use of dens (mean = 8.20 ± 6.01) than in the mid-range area (number of dens, mean = 0.90 ± 0.94; frequency, mean = 1.27 ± 2.12) and the boundary area (number of dens, mean = 0.34 ± 0.53; frequency, mean = 0.45 ± 0.93) of the home range. We discuss our results in terms of the importance of dens in facilitating escape from Coyotes. These results illustrate the need for examining den site selection at multiple scales to determine all selection factors, and to provide information useful for recovery and management efforts for this species.