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Introduction
Dispersal is fundamental to the genetic viability, persistence and size of populations (Harrison, 1991; Morris, 1991; Hanski, 1999). While an animal may benefit from leaving occupied habitat to seek out vacant territory, it can also encounter higher mortality rates that typically occur during dispersal (Krebs, 1978; Harris & Trewhella, 1988). Species distribution, and hence the potential success of reintroductions, is influenced by a species' ability to disperse successfully (Krebs, 1978). Because reintroductions are, by definition, conducted where conspecifics no longer occur (IUCN, 1998), a carefully planned reintroduction will release animals in areas where resources should be relatively abundant for the first released animals. As the population increases through additional releases or population growth, the habitat may become saturated and pressures to disperse may increase. Achieving connectivity for reintroduced populations of carnivores is difficult in fragmented landscapes because home range requirements are generally large and suboptimal habitat matrices between populations can serve as high mortality sink zones (Moehrenschlager & Somers, 2004).
Patches of optimal short-grass prairie habitat for swift foxes Vulpes velox are disjunct throughout the northern plains as a result of extensive cultivation, and populations of swift foxes may be isolated from one another because of an inability to cross a harsh cultivated matrix (Saunders et al., 1991). Furthermore, population isolation may lead to inbreeding depression thereby affecting the long-term persistence of disjunct populations (Keller & Waller, 2002).
The ability of swift foxes to disperse long distances is thought to be less than for larger canids (Mercure et al., 1993) and, in part because of limited gene flow, they have retained distinct species status from kit foxes Vulpes macrotis with which they interbreed in areas of New Mexico (Mercure et al., 1993). Reported dispersal distances for 48 juvenile kit foxes in California averaged only 7.8 ± SE 1.1 km (Koopman et al., 2000) and eight juvenile swift foxes in Colorado moved just 12.6 ± SE 3.2 km from their last known den to their first discovered den after movement ceased or death occurred (Schauster et al., 2002).
Swift foxes are listed as an Endangered Species in Canada and reintroduction efforts began in 1983. Swift foxes are not listed under the Endangered Species Act in the USA but they...