Population ecology of swift foxes (Vulpes velox) in southeastern Colorado

Abstract

Swift foxes (Vulpes velox) were once distributed across most of the shortgrass prairie of North America. The arrival of settlers and the concurrent loss of habitat, trapping, incidental poisoning, and shooting brought about a decline in its numbers until the swift fox remained only in the southern part of its historic range. A current understanding of swift fox population ecology is important to management and conservation efforts. We examined the population ecology of swift foxes on a native shortgrass prairie ecosystem in southeastern Colorado. From January 1997 to December 1998 we investigated home-range size and space use, spatial overlap, dispersal patterns, survival rates, and reproduction using a sample of 90 (42 males, 48 females) radio-collared foxes. Home ranges were largest (9.4 ± 4.9 km 2 ) and spatial overlap was greatest using nighttime locations when foxes were active, while daytime locations indicated that the use of dens was exclusive among social units, and space use (2.8 ± 2.2 km 2 ) was reduced during the day. Among resident foxes, survival rates were higher for adults than for juveniles. For dispersing foxes, adults that dispersed had higher survival rates than juvenile dispersers. Social units ranged in size from 2 to 4 foxes. About 58% of the social units produced pups; litter size averaged 2.4 pups at den emergence. Among the surviving pup cohort, some pups were philopatric, some dispersed long distances, while others dispersed to neighboring territories. Swift fox density was negatively associated with both coyote (Canis latrans) and lagomorph abundance but positively correlated with rodent abundance.Résumé : L'aire de répartition du renard véloce (Vulpes velox) s'étendait jadis à toute la prairie à herbes courtes de l'Amérique du Nord. L'arrivée des colons et, en conséquence, la perte d'habitats, le trappage, les empoisonnements accidentels et la chasse, ont réduit les densités du renard au point où il ne survit plus que dans la partie sud de son aire traditionnelle. Pour des fins de gestion et de conservation, il importe de connaître l'écologie actuelle de l'espèce. Nous avons donc étudié l'écologie d'une population d'un écosystème naturel de prairie à herbes courtes du sud-est du Colorado. Un échantillon de 90 (42 males : 48 femelles) renards munis de colliers radio-émetteurs nous a permis, de janvier 1997 à décembre 1998, de déterminer la taille du domaine vital, l'utilisation de l'espace, les chevauchements spatiaux, les patterns de dispersion, les taux de survie et la reproduction. La taille des domaines (9,4 ± 4,9 km 2 ) et les recouvrements de domaines étaient aximaux lorsque calculés à partir des repérages de nuit au moment où les renards étaient actifs; les repérages de jour indiquaient que l'utilisation des terriers était réservée exclusivement à chacun des groupes sociaux et que l'utilisation de l'espace (2,8 ± 2,2 km 2 ) était réduite durant le jour. Chez les renards résidants, les taux de survie étaient plus élevés chez les adultes que chez les jeunes. Les adultes...

Serologic Survey for Canine Infectious Diseases among Sympatric Swift Foxes (Vulpes velox) and Coyotes (Canis latrans) in Southeastern Colorado

“…Coyotes (Canis latrans) are medium-sized canids that occupy most habitats and regions of North America and are sympatric with swift foxes. Predation by coyotes is a leading cause of mortality in many swift fox populations (Covell, 1992;Sovada et al, 1998;Schauster et al, 2002). Resource partitioning between these two species has been documented to be intense, with coyotes possibly influencing the abundance and distribution of swift foxes across local landscapes (Kitchen et al, 1999;Kamler, 2002;Schauster et al, 2002;Karki, 2003).…”

“…Swift foxes were captured with box traps baited with chicken or an enclosure trap system (Covell, 1992;Schauster et al, 2002). A 3-4-ml blood sample was extracted from captured foxes via the jugular vein.…”

“…Although we did not document direct mortality among the swift foxes that was caused by CPV or CAV infection, foxes in a weakened condition from infection could be more vulnerable to predation. Coyote predation is the leading cause of swift fox mortality on the PCMS (Kitchen et al, 1999;Schauster et al, 2002;Karki, 2003). Predation could potentially mask an underlying infectious disease that increased the vulnerability of the foxes.…”

Swift Foxes and Ideal Free Distribution: Relative Influence of Vegetation and Rodent Prey Base on Swift Fox Survival, Density, and Home Range Size

“…Prior to this, both the maneuver site and the surrounding area had been grazed by domestic livestock since the late 1800s [18]. Livestock were excluded in 1983 and training began in 1985 [17].…”

“…All calculated ranges were based on a minimum of 30 locations. Previous area-observation analyses [18] indicated 31 locations were the minimum needed to estimate an individual, unbiased swift fox home range. All ranges used in analyses were based on the 95% fixed kernel isopleth [24] using a leastsquares cross-validation smoothing parameter.…”