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

Abstract

The grasslands of southwestern Saskatchewan, Canada are home to several snake species of conservation concern at the northern extreme of their geographic range. To aid conservation assessment and management planning for these snakes, we used radio‐telemetry, a geographic information system, and multivariate modeling to identify and compare macrohabitat selection by eastern yellow‐bellied racers (n = 33; Coluber constrictor flaviventris), bullsnakes (n = 16; Pituophis catenifer sayi), and prairie rattlesnakes (n = 23; Crotalus viridis). All 3 species shared communal hibernacula in the inactive winter season, but dispersed into different macrohabitats across the landscape during the spring and summer. Their home ranges varied in size by species and were dumbbell‐shaped with activity centers near hibernacula and in well‐defined summer grounds; activity centers were connected by narrow movement corridors. Racers strongly selected for riparian areas, bullsnakes selected for valley grassland habitats, and rattlesnakes selected for areas associated with prairie dog colonies. Some rattlesnakes traveled great distances (over 11 km) from the dens compared to the other species (bullsnake max. = 4 km; racer max. = 5 km), which may be a result of their selected macrohabitat being more patchily distributed in the landscape. Our results indicate that management plans for these snakes must consider the den area, corridors, and separate summering grounds, as well as differences in home range size and movement patterns for each species. © 2013 The Wildlife Society.

Conservation genetics of the eastern yellow-bellied racer (Coluber constrictor flaviventris) and bullsnake (Pituophis catenifer sayi): River valleys are critical features for snakes at northern range limits

“…Connectivity between river valleys has not been previously investigated, but is critical to understand for conservation planning. Agricultural habitats are avoided by both species [ 20 , 23 ], which may exacerbate long-standing isolating factors. Individuals occupying each river valley may therefore represent genetically differentiated populations that require individual management strategies.…”

“…Elaphe obsoleta obsoleta ; [ 18 ], Gloydius halys ; [ 19 ]). In addition, landscapes containing both suitable hibernacula and summer habitat for northern snakes (e.g., [ 20 ]) may be patchily distributed at range margins, a situation that is exacerbated by human activities that cause habitat loss and fragmentation [ 21 ]. Thus, gene flow may only occur among northern snake populations when individuals travel long distances away from dens to breed; however, successful dispersal may be uncommon, resulting in highly subdivided populations.…”

“…Interestingly, several recent studies have shown that some snake species have much larger home ranges and travel long distances from hibernacula at northern range limits (e.g. [ 20 , 22 – 24 ]). In principal, these behavioural traits may partially counteract the barriers to gene flow discussed above.…”

“…Almost nothing is known about population size, structure, or the degree of isolation of either species in this region. Both racers and bullsnakes have specific habitat requirements, including hibernacula with particular characteristics (thermal properties), and they often exhibit a high degree of fidelity to these sites [ 20 , 23 ]. Large geographic distances separate river valleys and hibernacula, which may be further isolated due to extensive land conversion for agriculture, creating an inhospitable landscape for snake dispersal.…”

Bullsnake Enjoying a Meal

“…Recent research efforts in Saskatchewan's Frenchman River Valley have shown that bullsnakes move extensively between overwintering dens and summer habitat, requiring much more space to carry out their lifecycle than previously suspected. 2,3…”