Effects of Artificial Escape Dens on Swift Fox Populations in Northwest Texas

Abstract

Throughout the range of swift fox (Vulpes velox), coyotes (Canis latrans) are the primary source of swift fox mortality. Coyotes may suppress swift fox populations where densities are high. Because coyote numbers have increased since wolves (Canis lupus) have been exterminated, we hypothesized that escape habitats may limit swift foxes. To test our hypothesis, we installed artificial escape dens in 3 spatially separated (treated) areas on the Rita Blanca National Grasslands in Dallam County, Texas, USA. From January 2002 to August 2004, we captured, radiocollared, and monitored 55 swift foxes. Annual swift fox survival in artificial escape-den—treated areas (Ŝ = 0.81) was higher than in untreated areas (Ŝ = 0.52, P = 0.07). Relative swift fox abundance was higher in treated than untreated areas in 2002 (Yates' χ2 = 4.61, P = 0.03) and in 2003 (Yates' χ2 = 4.70, P = 0.03) but not in 2004 (Yates' χ2 = 2.67, P = 0.10). However, recruitment rates were no different between treated and untreated areas in 2002 (Yates' χ2 = 0.21, P = 0.65) or 2003 (Yates' χ2 = 0.41, P = 0.52). Ninety-five percent fixed-kernel estimates of home-range sizes revealed no difference (P = 0.91) between treated and untreated areas, but swift foxes increased their distribution by moving into an area that had been unoccupied for at least 3 years before this study. Our results suggest that artificial escape dens contributed to increasing swift fox distributions in our study area.