Garter Snake (Thamnophis spp.) Surveys at Historical Den Sites in Alberta, 2017–2019
Alberta’s snakes are at the geographic edge of their North American range and have evolved effective strategies to survive the winter in a seasonally cold climate. In response to changing seasons and the onset of freezing winter temperatures, snakes enter a period of dormancy in underground spaces called dens (hibernacula). Dens play a critical role in the annual lifecycle of snakes. Obtaining reliable information on the location and occupancy of snake dens is an important first step to minimize snake mortality and the destruction or degradation of these important habitats. Between 2017 and 2019, we assessed the occupancy (snakes present/not detected) of 84 historical den records for red-sided (Thamnophis sirtalis), Plains (T. radix), and wandering garter snakes (T. elegans) stored in the Government of Alberta’s Fisheries and Wildlife Management Information System database. We used repeated surveys within the same season to verify the presence of at least one species of snake at each den record. We detected snakes at 40 (48%) dens, but were unable to detect snakes at 37 (44%) of the sites searched. Anthropogenic factors resulted in 7 (8%) of the 84 dens being destroyed or abandoned. Some level of imperfect detection (surveyors being unable to detect the presence of snakes at occupied dens) is assumed. Consequently, our findings are not intended as a final statement of species absence at dens. We caution that periodic natural catastrophes, or other events, may cause dens to become unusable by snakes. Conversely, the potential formation of new den habitat may occur through natural processes and anthropogenic activities in the immediate vicinity of extirpated dens. As such, the results presented within this report are temporary.