Executive summary

Recovery Strategy for the Gray Ratsnake (Pantherophis spiloides) – Carolinian and Frontenac Axis populations in Ontario

Prepared by T. Kraus, B. Hutchinson, S. Thompson and K. Prior

The Gray Ratsnake is a large snake that is native to North America and in Ontario it is only found in two locations: the Carolinian forest and Frontenac Axis. It is Ontario’s largest snake and can grow to 185 centimetres in length. It has keeled scales and a powerful slender body with a wedge-shaped head. The body tends to be more square than round in cross section. Hatchling Gray Ratsnakes have a pattern of dark grey or black blotches and spots over a background of light gray. As the snake ages, this pattern fades and adults are predominantly black. The underneath of the chin and throat are usually white, often mottled with grey and black blotches. They can live up to 30 years, and reach maturity at about seven years. Mating occurs between late May and mid- June and females usually reproduce every two to three years.

The Frontenac Axis population of Gray Ratsnakes was listed as threatened in 2009 under Ontario’s Endangered Species Act, 2007 and the Carolinian population was listed as endangered. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the Frontenac Axis population as threatened and the Carolinian population as endangered in 2007.

The Gray Ratsnake requires a mosaic of habitat features, including forest and edge habitat. Mature females require oviposition (egg-laying) sites, typically rotten interior cavities of large deciduous trees and stumps or compost piles. This species overwinters underground in communal hibernacula and shows high fidelity to those hibernacula.

Life history features such as late age of maturity, long life span, biennial reproduction and intermittent juvenile recruitment predispose Gray Ratsnake populations to major demographic fluctuations when subjected to disturbances and do not allow for a natural capacity to rapidly rebound from demographic low points.

Threats to the Gray Ratsnake include habitat degradation, fragmentation and loss, direct mortality, road mortality and disturbance or destruction of hibernacula. Knowledge gaps relate to population persistence and viability measures, efficacy of mitigation measures and juvenile and neonate ecology. A number of recovery actions have been completed or are underway and range from stewardship and outreach activities to habitat and genetic research.

The recovery goal for the Gray Ratsnake in Ontario is to retain the current distribution, population size and connectivity among extant sub-populations within the Frontenac Axis population of eastern Ontario and to achieve self-sustaining sub-populations in the Carolinian population by increasing the distribution and size of the population.

Protection and recovery objectives that guide the approaches to recovery are to:

  1. Develop and implement a coordinated monitoring plan focused on population indices and distribution, habitat stresses and efficacy of recovery actions;
  2. Conduct research to fill knowledge gaps including ecological studies of habitat, genetic connectivity and the impacts of various threats;
  3. Describe and map habitat required to meet recovery goals for each of the Ontario populations;
  4. Protect and manage the habitat of the species and mitigate priority threats; and
  5. Improve the delivery and evaluation of stewardship and communications to increase awareness, land stewardship, application of best management practices and citizen science efforts.

A number of approaches are identified for each of these objectives.

It is recommended that the area prescribed as Gray Ratsnake habitat in a habitat regulation include all known hibernacula and the area within a 150 metre radius of them; and all known oviposition sites and the area within a 30 metre radius of them. In addition, for the Carolinian population, the area prescribed as habitat in the regulation should also include all natural features (e.g., woodlands, wetlands, hedgerows, meadows) within five kilometres of known hibernacula, oviposition sites and locations at which a Gray Ratsnake has been observed (accurate to 100 metres). For the Frontenac Axis population, a map based on quantified measures of preferred habitat including indices of suitable habitat, road density, measures of connectivity and likelihood of supporting existing populations is included in the strategy. It is recommended that cells in the map with suitable habitat (cell value of 0.5 or greater) be prescribed as habitat in a habitat regulation for the population. This area is roughly bordered by Highway 7 in the north, the St. Lawrence River in the south, Highway 38 and in the west and Highway 29 in the east.