Winter movement behavior by swift foxes (Vulpes velox) at the northern edge of their range

Abstract

Winter can be a limiting time of year for many temperate species, who must access depressed prey resources to meet energetic demands. The swift fox (Vulpes velox (Say, 1823)) was extirpated from Canada and Montana (USA) by 1969, but was reintroduced in the 1980s to Canada, and subsequently spread into northern Montana. Swift foxes in this region are at the current northern range edge where winter conditions are harsher and persist longer than in their southern range (i.e., Colorado (USA) to Texas (USA)). We collected fine-scale locational data from swift foxes fitted with global positioning system collars to examine movement and resource-use patterns during winter of 2016–2017 in northeastern Montana. Our results suggest that swift foxes displayed three distinct movement patterns (i.e., resting, foraging, and travelling) during the winter. Distance to road decreased relative probability of use by 39%–46% per kilometre across all movement states and individuals, whereas the influence of topographic roughness and distance to crop field varied among movement states and individuals. Overall, while our findings are based on data from three individuals, our study suggests that across movement states during the critical winter season, swift foxes are likely using topography and areas near roads to increase their ability to detect predators.

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

“…While there is no study documenting the effects of red foxes on swift foxes, and we did not have data to do so, we hypothesize that red foxes may have a negative impact on swift foxes as well, through interference and exploitative competition. The importance of contiguous grassland was further supported in a concurrent study where we were able to document potential dispersal movements by two adult foxes that moved 25 km south toward the Milk River, but then moved back to their area of origin (Butler, 2019). This suggests that agricultural development along the Milk River at the southern extent of our population might be a barrier to recolonization both behaviorally in terms of movement, as well as demographically in terms of reduced survival.…”

“…Our study indicates that the population of swift foxes in north-eastern Montana is currently stable, but likely not producing enough individuals to successfully expand southward into unoccupied habitat that is suitable based on previous habitat assessments (Alexander et al, 2016;Butler, 2019). In source-sink theory, source populations occur in areas where reproduction is greater than mortality, and there is a surplus of juveniles in the population that disperse to other areas (Pulliam, 1988).…”

“…Moehrenschlager (2000) found 64% of swift fox juveniles remained in their natal range into the winter, and all the juvenile foxes we were able to monitor into spring remained in the area where we caught them (Butler et al, 2020), which may have led to their relatively high survival rates (Table 3). Thus, the stable growth rate we observed suggests that the population is likely not acting as a source population for the region; and could explain why despite there being suitable habitat in the gap between populations (Alexander et al, 2016;Butler, 2019), areas south of our study area remain unoccupied.…”

“…During the study, we had issues with some collar batteries dying prematurely (Butler et al ., 2019). We expected collars to last at least 6 months, but several collars had batteries that died or lost their VHF antennas in the first 3 months.…”

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

“…Similarly, our findings suggest that swift foxes might be negatively impacted by extensive conversion of CRP fields to row-crop agriculture. However, at a fine spatiotemporal scale, swift foxes in this region might at least temporarily use harvested row crop fields ( Butler et al 2019 ). Thus, the impact of conversion of native prairie to row-crop agriculture might not only be felt at a local scale, but at the landscape scale, given the large average home range size of swift foxes in this area.…”