Spatial distribution and abundance of Common Sharp-tailed Snakes (Contia tenuis) on Observatory Hill, Vancouver Island, British Columbia

Abstract

Similar to many small, secretive snakes, the natural history and population biology of Sharp-tailed Snakes are poorly known. Information on habitat use and patterns of abundance are particularly important for management and recovery of this species listed as endangered in Canada. We surveyed for snakes from October 2010 to March 2019 using a microhabitat-based array of 162 artificial cover-object stations. The surveys (236 array checks) resulted in 177 detections of Sharp-tailed Snakes, representing 106 individuals identified through pattern mapping. Body size (snout-vent length) of the snakes ranged from 82 mm to 261 mm, and most (65.1%) were adults >180 mm. The dispersion of snakes among sampling stations was aggregated over time with 42 stations used by one to 15 individuals over the course of the study, including three “hot spots” used by over ten individuals; these sites represented hibernation and possibly also egg-laying sites. Most detections were on the warmer west and south slopes of the hill and were correlated with the presence of talus but not with other habitat attributes examined. The population sampled by the array was estimated to consist of a mean of 128 snakes (6.04/ha) in 2011 and 80 (3.80/ha) in 2018 with mean annual survival rate of 52.9%. We suggest focusing survey efforts on stable talus patches with south- and west-facing aspects both to locate the species at new sites and to identify important habitats at known sites.