Gray ratsnake (Elaphe spiloides) COSEWIC assessment and status report: chapter 2

Species Information

The Gray Ratsnake (Elaphe spiloides) is the largest snake in Canada, reaching a maximum snout-vent length (SVL) of approximately 190 cm. The colour pattern of adult Eastern Ratsnakes is widely variable across the species’ range. Throughout all populations in Canada, adult Gray Ratsnakes are typically plain, shiny black with white, yellow, orange or red colouration on the skin between the scales. The ventral surface is typically white or yellowish with a clouded grey or brown pattern, often resulting in a checkerboard appearance. Ratsnakes can often be distinguished from other snakes by their throat, which has a plain white or cream colour. In contrast to adults, juveniles are dorsally patterned with dark grey or brown blotches on a pale grey background.

Distribution

The Gray Ratsnake is widely distributed and commonly found throughout the forested areas of the eastern and central United States. However, within Canada, the Gray Ratsnake is confined to two geographically disjunct regions in southwestern (Carolinian Faunal Province) and southeastern (Great Lakes/St. Lawrence Faunal Province) Ontario. In this report, populations from these two regions will be treated as two Designatable Units referred to as the Carolinian and Great Lakes/St. Lawrence populations. In southwestern Ontario, the Carolinian population is associated with the Carolinian forest along the northern edge of Lake Erie and is limited to four very small, isolated populations in Middlesex, Elgin, Haldimand-Norfolk and Niagara counties. The Great Lakes/St. Lawrence population is associated with the Frontenac Axis in Frontenac, Lanark, and Leeds and Grenville counties.

Habitat

The Gray Ratsnake is semi-arboreal and typically found in a wide variety of woodland habitats across its range. At the home range scale, they seem to prefer a mosaic of forest and open habitat (fields; bedrock outcrops) with a high amount of edge. Detailed studies of habitat use on the Frontenac Axis have established that ratsnakes require a variety of habitat types throughout their life cycle. In winter, ratsnakes hibernate below ground in communal hibernacula that provide shelter from both freezing temperatures and dehydration. During the active season, individuals seek shelter in standing snags, hollow logs, rock crevices and under rocks to avoid high temperatures and predators. Females nest in decaying matter inside standing snags, stumps, logs and compost piles where conditions are humid and temperatures are approximately 30ºC.

Biology

Gray Ratsnakes reach maturity in approximately 7-9 years. Once sexually mature, females produce a clutch of 8-15 eggs every 2-3 years. In Ontario, females nest in early July to early August, approximately one month after the mating season, which spans from late May to early June. The eggs hatch between late August and late September following an incubation period of around 60 days.

The harsh climate in Canada restricts the active season of ratsnakes to approximately 5 months (May – October). During this active season, ratsnakes have relatively large home ranges (~18 ha) and disperse as far as 4 km from their hibernacula. Adults demonstrate strong site fidelity by often using the same home range locations both within and between years.

Gray Ratsnakes are both predators and prey of numerous species. They feed mainly on small mammals (~65%) and birds (~30%) and known predators include a number of large birds of prey (e.g. red shouldered hawk (Buteo lineatus), osprey (Pandion haliaetus), red tailed hawk (Buteo jamaicensis)) and medium-sized mammals (e.g. fisher (Martes pennanti), mink (Mustela vison)).

Population Sizes and Trends

Due to the secretive nature of snakes, it is extremely difficult to estimate the extent and size of populations accurately. Based on habitat suitability models and density estimates, the Great Lakes/St. Lawrence population has been estimated to contain between 25 000 – 85 000 individuals. Although no population-wide census information is available, 2 populations on the Frontenac Axis were shown to be declining slightly over an 18-year period. No demographic sampling has been conducted on the Carolinian populations. However, based on the amount of suitable habitat available and the small number of sightings, these populations are likely small and declining.

Limiting Factors and Threats

Life-history characteristics such as biennial reproduction, delayed age at maturity (~7 years) and slow growth rates make Canadian populations of Gray Ratsnakes particularly sensitive to disturbances. Mortality caused by increased contact with humans (e.g. road mortality, destruction of hibernacula, deliberate killing of ratsnakes by people) can therefore have significant impacts on populations. Furthermore, the suitable habitat in the Carolinian region is severely restricted and heavily fragmented, and it is unknown whether enough habitat remains to support viable populations of ratsnakes. Suitable habitat on the Frontenac Axis is much more abundant, but increased recreational activity in the area has led to increased development and will likely reduce and fragment the existing habitat.

Special Significance of the Species

Both the Great Lakes/St. Lawrence and Carolinian populations are geographically isolated and genetically distinct from each other and from populations in the United States. Both populations are therefore valuable for the preservation of the total genetic diversity of this species. Gray Ratsnakes also contribute significantly to the ecological communities in which they exist. They are generally near the middle of the food chain and are both predators and prey of numerous species. Gray Ratsnakes require large continuous tracts of land and, therefore, any efforts toward preservation would benefit many other species.

Existing Protection

The Gray Ratsnake does not have a global rank, but individual states within the range of the species list ratsnakes as secure (S5) or apparently secure (S4), except in Wisconsin where they are listed as imperiled (S2) (ratsnakes have not been ranked or are under review in some States).Within Canada, they are protected under Schedule 1 (Threatened) of the Species at Risk Act (SARA), ranked within Ontario as S3 (NHIC) and as Threatened by the Committee on the Status of Species at Risk in Ontario (COSSARO). They are also protected in Ontario under the Fish and Wildlife Conservation Act, in which Elaphe spiloides is listed as a “Specially Protected Reptile under Schedule 10). Very little (< 5%) of the Canadian range of ratsnakes is within protected areas.