Comparative Ecology of Three Sympatric Snake Species in Southwestern Saskatchewan

Abstract

My research focused on the comparative ecology of three sympatric snake species which are of conservation concern in southwestern Saskatchewan: eastern yellow-bellied racers (Coluber constrictor flaviventris), a Threatened species in Canada; bullsnakes (Pituophis catenifer sayi), Data Deficient, and; prairie rattlesnakes (Crotalus viridis), yet to be assessed, but considered a high priority candidate. Few studies on snake ecology have collected data for multiple species at the same site, a factor potentially important for understanding resource partitioning and competition between sympatric species. Furthermore, identifying which resources elicit competition may be critical for the conservation and management of endangered species. I used radio-telemetry, GIS, and multivariate modeling to identify and compare habitat use by racers (n = 33), bullsnakes (n = 16), and rattlesnakes (n = 23) in and around Grasslands National Park, Saskatchewan, Canada. Used and available macrohabitat sites were compared to quantify habitat use by these species. I found that although all species hibernate in communal den sites, during the active season they disperse into different macrohabitats across the landscape. As a result, home ranges were dumbbell-shaped with activity centers near hibernacula and in well-defined areas used in summer, and these centers of activity were connected by narrow corridors. Bullsnakes had the smallest home range (4.6 ± 0.7 ha), while racers (14.2 ± 0.9 ha) and rattlesnakes (13.9 ± 1.5 ha) were similar. Racers strongly selected for riparian areas, bullsnakes tended to inhabit valley grassland habitats, and rattlesnakes tended to be associated with prairie dog colonies. Some rattlesnakes travelled great distances (over 11 km) from the dens compared to the other species (bullsnake maximum = 4 km; racer maximum = 5 km), which may be a result of the macrohabitat selected being more patchily distributed in the landscape. In addition, I identified microhabitat selection by rattlesnakes which selected for sites with cover (e.g. shrubs and burrows) along the edges of prairie dog colonies. The habitat use by the three species I studied is consistent with habitat partitioning during the active season, though overlap does occur at the overwintering sites and in movement between selected macrohabitats. In addition to the general ecological value of my findings, the results of this study will be useful in aiding designation of critical habitat for the eastern yellow-bellied racer and contribute to assessment of bullsnakes and prairie rattlesnakes in Canada.