Home range size and resource use by swift foxes in northeastern Montana

Abstract

<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

Life on the edge: habitat fragmentation limits expansion of a restored carnivore

“…In accordance with our predation risk hypothesis, survival was best explained by the amount of grassland within a fox's area of use (Table 1), which was also the strongest predictor of resource use by swift foxes in the region (Butler et al ., 2020). Previous studies have also shown that swift foxes prefer short‐ and mixed‐grass prairies over other cover types because grasslands increase the ability to visually detect predators, provide swift foxes with denning opportunities and enhance population connectivity (Kitchen et al ., 1999; Russell, 2006; Thompson & Gese, 2007; Sasmal et al ., 2011; Schwalm, 2012).…”

“…In an effort to re‐sight collared individuals that had collar failure and might still be alive, when we had not located a fox after a month, we deployed three baited, heat and motion‐activated camera traps (TrophyCam, Bushnell, Overland Park, KS, USA) within a fox’s known primary area of use or suspected area of use for 2 weeks. We determined these areas based on GPS data downloaded from the collars (Butler et al ., 2020), any locations determined from the VHF signal or proximity to the original trapping location if we did not have GPS or VHF locations. If we detected the fox, then we kept cameras active until the fox was no longer detected.…”

“…We estimated the 12‐month survival rates for adults and the 6‐month survival rates for juveniles, as has been done in other swift fox studies (Sovada et al ., 1998; Kamler et al ., 2003 a ). To evaluate support for our hypothesis that swift fox survival was enhanced by selecting habitats at the third order (Johnson, 1980) that increased the probability of detecting predators as opposed to maximizing access to prey resources (Thompson & Gese, 2007), we evaluated the influence of the percentage of native grassland within a 1‐km radius moving window (PG), topographic roughness (TRI) and normalized difference vegetation index (NDVI; see Butler et al ., 2020 for full description of how these variables were estimated) on swift fox survival. We predicted that the percentage of grassland would have a positive influence on survival because more contiguous grasslands minimize the influence of tall cultivated crop fields, which increases predator detection.…”

“…There is less research on the influence of anthropogenic development, such as roads and natural gas development, on predation risk. Previous studies have found that swift foxes make use of roads and areas near roads and gas wells (Hines & Case, 1991; Sasmal et al ., 2011; Butler et al ., 2020), but previous studies have found that coyotes use roads as well (Grinder & Krausman, 2001; Hinton, Van Manen & Chamberlain, 2015; Murray & St. Clair, 2015). One hypothesis for why swift foxes select for areas closer to development is that these features provide a ‘human shield’ (Berger, 2007; Moll et al ., 2018), where human presence and activity associated with these features may cause coyotes to avoid these areas in rural landscapes typical of the Great Plains.…”

“…It is hypothesized that as an intermediate predator, swift foxes select for resources that minimize predation risk, mainly from coyotes Canis latrans (the top predator of swift foxes, Kitchen, Gese & Schauster, 1999; Olson & Lindzey, 2002), rather than select for resources that maximize access to prey (Thompson & Gese, 2007). In accordance with this hypothesis, swift foxes are thought to minimize predation risk by increasing their ability to visually detect their predators and decrease lethal encounters by avoiding prey‐rich areas (Kamler et al ., 2003 a ; Russell, 2006; Thompson & Gese, 2007; Sasmal et al ., 2011; Butler et al ., 2020). There is less research on the influence of anthropogenic development, such as roads and natural gas development, on predation risk.…”