Swift Fox Populations Research Articles

Indexing Swift Fox Populations in New Mexico Using Scats

We examined collection of scats (feces) as a survey method for indexing statewide populations of swift foxes (Vulpes velox). We searched for scats on 99 transects throughout the range of swift foxes in New Mexico. Swift fox scats were found on 79.8% of transects. Scats confirmed by DNA analysis to have originated from swift foxes were found on 59.6% of transects. Statistical power was sufficient to detect a 20% decline in the proportion of transects with swift fox scats or a 7% decline in the total number of scats collected over the entire range. The proportion of transects with scats and the total number of scats collected may be useful as indices of relative swift fox population abundance. Average number of scats found per collection site was not found to be a useful index due to large variations between sites in the numbers of scats found. Confirmation of swift fox presence by DNA analysis does not appear to be necessary for transects with >7 scats, as all transects with >7 scats had at least one confirmed swift fox scat. Collection of scats appears to be a useful technique for indexing populations of swift foxes in New Mexico.

Impacts of Coyotes on Swift Foxes in Northwestern Texas

The distribution of swift foxes (Vulpes velox) in the western Great Plains has been dramatically reduced since historical times. Because coyotes (Canis latrans) have been identified as the main cause of mortality in swift fox populations, we studied the impacts of coyotes on swift foxes in northwestern Texas, USA. We radiomarked and monitored 88 swift foxes and 29 coyotes at 2 study sites from 1998 to 2000. On site 1, coyotes had relatively high abundance (41 ± 6.8 scats/2 km) and survival (0.90), whereas swift foxes had low survival (0.47), low density (0.24-0.31 foxes/km 2 ), and low recruitment (0.25 young/adult), and killings by coyotes (n = 8) were the major cause of death. On site 2, coyotes had relatively low abundance (19 ± 4.9 scats/2 km) and survival (0.54) due to greater human persecution, whereas swift foxes had relatively high survival (0.69), high density (0.68-0.77 foxes/km 2 ), and high recruitment (1.3 young/adult), and few (n = 2) were killed by coyotes. Our initial results -. suggested that swift foxes benefited from lower coyote numbers. To test this hypothesis, we removed 227 coyotes on site 1 during the final year of our study. Subsequently, coyote abundance decreased (18 ± = 4.5 tcats/2 km), whereas swift foxes had increased survival (0.63), increased density (0.68 foxes/km 2 ), arid increased recruitment (1.2 young/adult), and few (n = 3) were killed by coyotes. All parameters remained consistent on site 2. Our results indicate that coyotes can suppress swift fox populations, and that reductions in coyote numbers can change a swift fox population from a sink to a source.

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

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 km2) 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 km2) 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.

SWIFT FOX SURVIVAL AND PRODUCTION IN SOUTHEASTERN WYOMING

Abstract We estimated annual survival rates of swift foxes (Vulpes velox) and documented number of young per pair in a transition zone between shortgrass prairie and sagebrush steppe plant communities in southeastern Wyoming during 1996–2000. Annual adult survival ranged from 40% to 69%, with predation by coyotes (Canis latrans) the primary cause of deaths. Two foxes died of canine distemper virus. Annual survival rates did not differ among years (P > 0.12). Nineteen of 24 (79%) swift fox pairs were observed with young over 3 years. Mean minimum litter size was 4.6 based on these 19 litters and 6 others not associated with our radiocollared foxes. Adult survival was similar and litter size slightly larger than observed elsewhere in the species range, suggesting that viable swift fox populations can be supported by sagebrush steppe and shortgrass prairie transition habitat.

Causes and Rates of Mortality of Swift Foxes in Western Kansas

Knowledge of mortality factors is important for developing strategies to conserve the swift fox (Vulpes velox), a species being considered for listing under the Endangered Species Act, but available information about swift fox mortality is inadequate. We used radiotelemetry techniques to examine the magnitude and causes of mortality of swift fox populations in 2 study areas in westem Kansas. One study area was predominantly cropland, the other rangeland, Mortality rates, calculated using Kaplan-Meier estimation techniques in a staggered entry design, were 0.55 ± 0.08 (x ± SE) for adult and 0.67 ± 0.08 for juvenile swift foxes. We did not detect differences between study areas in mortality rates for adults or juveniles. Predation by coyotes (Canis latrans) was the major cause of mortality for adult and juvenile swift foxes in both study areas, and vehicle collision was an important mortality factor for juveniles in the cropland study area. No mortality was attributed to starvation or disease.

GENETIC SUBDIVISIONS AMONG SMALL CANIDS: MITOCHONDRIAL DNA DIFFERENTIATION OF SWIFT, KIT, AND ARCTIC FOXES.

Gene flow can effectively suppress genetic divergence among widely separated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Using mtDNA restriction-site and sequence analyses, we evaluate the extent of divergence among populations of two small relatively sedentary North American canids, the kit and swift foxes (genus Vulpes). We determine the significance of genetic differentiation among populations separated by distance and those separated by discrete topographic barriers. Our results show the among-population component of genetic variation in kit and swift foxes is large and similar to that of small rodents with limited dispersal ability. In addition, we found two distinct groupings of genotypes, separated by the Rocky Mountains, corresponding to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar populations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited geographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alopex lagopus), a morphologically distinct species commonly placed in a separate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.