Long-range juvenile dispersal and its implication for conservation of reintroduced swift fox Vulpes velox populations in the USA and Canada D avid A usband and A xel M oehrenschlager Abstract Dispersal is fundamental to the persistence of wild populations. Historically, swift foxes Vulpes velox of the northern Great Plains of North America have been thought to be poor dispersers. Short-grass prairie is optimal habitat for swift foxes but can be fragmented in the northern Great Plains. We wanted to assess whether wild-born, juvenile swift foxes from two proximate but distinct reintroduced populations had potential to move from one population to the other. We found five animals exhibiting long bouts of dispersal, much further than averages previously reported. One female fox traversed the long distance between the two populations and survived for at least three breeding seasons in the wild. We believe our findings are significant for conservation because they show that swift foxes are not poor dispersers and that patches of short-grass prairie previously thought to be too isolated (. 25 km) for natural movement may be recolonized or be suitable for reintroductions of swift foxes. Keywords Connectivity, dispersal, fragmentation, reintro- duction, swift fox, Vulpes velox. Introduction D ispersal is fundamental to the genetic viability, per- sistence 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 rela- tively abundant for the first released animals. As the popu- lation increases through additional releases or population growth, the habitat may become saturated and pressures to disperse may increase. Achieving connectivity for reintro- duced 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 re- tained 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 are a Species of Concern in Montana and are of particular cultural significance to the Blackfeet Tribe in Montana, who began reintroducing swift foxes to Reservation lands in 1998. Recent studies and surveys have indicated swift fox reintroductions in both Canada and on the Blackfeet Reservation in Montana were successful (Moehrenschlager & Moehrenschlager, 2001; Ausband & Foresman, 2007a), with populations growing and expanding their distributions, although we believe there is still some vacant suitable habitat within both study areas. Swift fox densities near the Canadian release sites are high (Moehrenschlager & Moehrenschlager, 2006) and although density estimation was not a focus of research on the Blackfeet Reservation, relative density of swift foxes near and around (# 20 km radius) the origi- nal release site was high (D. Ausband, unpubl. data). Ge- netic viability and persistence of these two populations would be enhanced through an interchange of individuals. DAVID AUSBAND (Corresponding author) Wildlife Biology Program, University of Montana, 311C Forestry, Missoula, MT 59812, USA. E-mail david.ausband@mso.umt.edu AXEL MOEHRENSCHLAGER Centre for Conservation Research, Calgary Zoological Society, Calgary, Canada. Received 13 September 2007. Revision requested 30 November 2007. Accepted 7 January 2008. ª 2009 Fauna & Flora International, Oryx, 43(1), 73–77 doi:10.1017/S0030605308001622 Printed in the United Kingdom