RESUMEN
Swift foxes (Vulpes velox) are endemic to the Great Plains of North America, but were extirpated from the northern portion of their range by the mid-1900s. Despite several reintroductions to the Northern Great Plains, there remains a ~350 km range gap between the swift fox population along the Montana and Canada border and that in northeastern Wyoming and northwestern South Dakota. A better understanding of what resources swift foxes use along the Montana and Canada border region will assist managers to facilitate connectivity among populations. From 2016 to 2018, we estimated the home range size and evaluated resource use within the home ranges of 22 swift foxes equipped with Global Positioning System tracking collars in northeastern Montana. Swift fox home ranges in our study were some of the largest ever recorded, averaging (± SE) 42.0 km2 ± 4.7. Our results indicate that both environmental and anthropogenic factors influenced resource use. At the population level, resource use increased by 3.3% for every 5.0% increase in percent grasslands. Relative probability of use decreased by 7.9% and 7.4% for every kilometer away from unpaved roads and gas well sites, respectively, and decreased by 3.0% and 11.3% for every one-unit increase in topographic roughness and every 0.05 increase in normalized difference vegetation index (NDVI), respectively. Our study suggests that, to reestablish connectivity among swift fox populations in Montana, managers should aim to maintain large corridors of contiguous grasslands at a landscape scale, a process that likely will require having to work with multiple property owners.
RESUMEN
Sylvatic plague poses a substantial risk to black-tailed prairie dogs ( Cynomys ludovicianus) and their obligate predator, the black-footed ferret ( Mustela nigripes). The effects of plague on prairie dogs and ferrets are mitigated using a deltamethrin pulicide dust that reduces the spread of plague by killing fleas, the vector for the plague bacterium. In portions of Conata Basin, Buffalo Gap National Grassland, and Badlands National Park, South Dakota, US, 0.05% deltamethrin has been infused into prairie dog burrows on an annual basis since 2005. We aimed to determine if fleas ( Oropsylla hirsuta) in portions of the Conata Basin and Badlands National Park have evolved resistance to deltamethrin. We assessed flea prevalence, obtained by combing prairie dogs for fleas, as an indirect measure of resistance. Dusting was ineffective in two colonies treated with deltamethrin for >8 yr; flea prevalence rebounded within 1 mo of dusting. We used a bioassay that exposed fleas to deltamethrin to directly evaluate resistance. Fleas from colonies with >8 yr of exposure to deltamethrin exhibited survival rates that were 15% to 83% higher than fleas from sites that had never been dusted. All fleas were paralyzed or dead after 55 min. After removal from deltamethrin, 30% of fleas from the dusted colonies recovered, compared with 1% of fleas from the not-dusted sites. Thus, deltamethrin paralyzed fleas from colonies with long-term exposure to deltamethrin, but a substantial number of those fleas was resistant and recovered. Flea collections from live-trapped prairie dogs in Thunder Basin National Grassland, Wyoming, US, suggest that, in some cases, fleas might begin to develop a moderate level of resistance to deltamethrin after 5-6 yr of annual treatments. Restoration of black-footed ferrets and prairie dogs will rely on an adaptive, integrative approach to plague management, for instance involving the use of vaccines and rotating applications of insecticidal products with different active ingredients.