Habitat selection by grassland snakes at northern range limits: Implications for conservation

Abstract

Animal populations at northern range limits may use habitat differently from those at range cores, requiring distinct conservation plans. Snakes are ectotherms that often have very specific requirements, but few studies have focused on the effect of northern latitudes on habitat selection by grassland snakes. We studied movement and habitat selection of 2 sympatric snake species at their northern range limits on the North American Great Plains: the eastern yellow‐bellied racer (Coluber constrictor flaviventris, hereafter racer), a Threatened species in Canada, and the bullsnake (Pituophis catenifer sayi), which is listed as Data Deficient. Both of these species are potentially vulnerable to extinction in Canada because of habitat loss. Snakes from our study populations traveled up to 10‐times farther from winter dens and occupied home ranges 3–104 times larger than populations further south. Both snake species moved from winter dens in the slopes of a major river valley to habitat in adjacent lowlands, including riparian zones (racers) and hilly areas with native grass species (bullsnakes). Multivariate modeling revealed that proximity to retreat sites was a significant predictor of snake site use for both species. Considering the need for winter dens and summering areas, our data suggest that snakes in northern latitudes should ideally have much larger protected areas compared to snakes near the core of their range. An alternative strategy is to conserve corridors linking wintering dens and summer habitats. Retreat sites such as burrows and shrubs are critical components of local habitat and should be included in conservation plans. © 2011 The Wildlife Society.

Balancing the dumbbell: Summer habitats need protection in addition to winter dens for northern snake communities

“…Though suitable overwintering sites are imperative to the persistence of northern snake populations, small reserves around communal hibernacula have been identified as insufficient to protect snakes during the active season (Martino et al , Williams et al ); our results show that identifying summer grounds will likely require species‐specific considerations. Martino et al () suggested that simply creating management zones around dens alone would likely not be sufficient to include summer grounds for northern snake populations, and they further suggested that this can be mitigated by either defining much larger den zones or identifying a corridor system linking smaller protected areas surrounding winter and summer habitats. Our results show the home ranges of these northern grassland snakes are indeed dumbbell‐shaped, and management considerations must include the den area, corridors, and the summering grounds.…”

“…Roads were used according to their availability in the environment by racers and rattlesnakes. In contrast, compositional analysis revealed bullsnakes (data from Martino et al ) select for lowland pasture, hills and slopes, and roads, though lowland pasture ( t 15 = 3.434, P = 0.003) and hills and slopes ( t 15 = 4.830, P ≤ 0.001) were used more than roads. All 3 species avoided native upland, crop areas, irrigated areas, and open water, which were used significantly less than the other available landscape types (Table ).…”

“…Macrohabitats available to the snakes included native upland, lowland pasture, hills and slopes, mudflats, crop areas, prairie dog colonies, irrigation areas, open water, roads, and riparian areas. These macrohabitats are easily differentiated from each other in the mixed‐grass prairie ecosystem in southern Saskatchewan, and have been used in other grassland snake studies (e.g., Martino et al ). We determined the macrohabitat used by radio‐tracked snakes at each location by visual observation of the surrounding area, which we later confirmed by overlaying the snake locations on satellite imagery using ArcGIS Desktop 10.…”

“…We compared the movement patterns and macrohabitat selection of 3 sympatric snake species (racers, bullsnakes, and rattlesnakes) during the active season at the northern extreme of their ranges in the mixed‐grass prairie ecoregion of southern Canada. Martino et al () found that racers and bullsnakes travel up to 10 times farther from hibernacula and occupy much larger home ranges (3–104 times larger) than their southern counterparts. They proposed that this phenomenon may be because they use distinct winter and summer habitats linked by corridors, creating a dumbbell‐shaped home range.…”

Scale‐dependent Orientation in Movement Paths: A Case Study of an African Viper

“…), studies of movement patterns tend to be at relatively large spatial scales (10 2 –10 3 m) that emphasize differential habitat use, mate‐searching patterns, and migration between seasonal foraging‐, mating‐ and/or overwintering‐grounds (Reinert ; Glaudas & Rodríguez‐Robles ; Wastell & Mackessy ; Martino et al. ; Miller et al. ; Pittman et al.…”