A Conservation Action Plan for the Carolinian population of Gray Ratsnake

As one of the largest snake species in Ontario, adult Gray Ratsnakes (Pantherophis spiloides) are typically 1 to 2 m long, but some individuals have been known to reach lengths of up to 2.55 m! This species is slow to mature, taking 6 to 8 years to reach adulthood. The Gray Ratsnake is found at its northern range limit in Ontario, where it is divided into two designatable units, the Carolinian and the Great Lakes/St. Lawrence populations. The two populations are listed as Endangered and Threatened, respectively, under Canada’s Species at Risk Act. In Canada, designatable units identify "discrete" and "evolutionarily significant" populations. The Carolinian population is found within 100 km of the north shore of Lake Erie and is subject to extreme pressure from human threats, including habitat destruction and road mortality. The remaining Gray Ratsnake subpopulations within the Carolinian population are small, isolated, and vulnerable to extirpation.

Natural Resources Solutions Inc. (NRSI) is an environmental consulting firm with strong ties to the Carolinian Zone in Ontario and expertise in native reptiles. Their work with the Gray Ratsnake in this region over the past 10 years suggests that preventing the eradication of this unique population requires immediate, collaborative, and data-driven conservation action. NRSI engaged African Lion Safari, as a co-founder of the Conservation Planning Specialist Group Canada (CPSG Canada), to design and facilitate a Conservation Planning Workshop for Carolinian Gray Ratsnake using the globally recognized planning methods of the International Union for the Conservation of Nature’s Conservation Planning Specialist Group. A Population Viability Analysis (PVA) was developed as part of the process to provide a data-driven scientific framework to help guide management planning. CPSG Canada is the Regional Resource Center of the IUCN Conservation Planning Specialist Group (CPSG).

In collaboration with CPSG Canada, NRSI brought together a group of species and local experts to assist in developing the PVA and an updated threat assessment for the Carolinian population of Gray Ratsnake to underpin management planning. The PVA provided guidance on how population growth and genetic diversity might be affected under different management scenarios, including augmentation that helped guide conservation action planning.

Over five virtual sessions in 2025, experts collaboratively collated information for the remaining isolated locations of the Carolinian population. Results suggested that without additional urgent and intensive recovery actions, many of the subpopulations within Carolinian Canada are likely to become extirpated within 30 years. Due to the species life-history traits (e.g., age at sexual maturity), the PVA suggested that subpopulations must include at least 70 individuals to maintain 90% genetic diversity over 30 years. The PVA also investigated the effect of intervention in the form of adding snakes to the population by way of augmentation, and specifically, by adding/releasing juvenile snakes. The method of augmentation was not considered in the PVA but discussion among experts at the workshop suggested this could best be accomplished by head-starting wild eggs or neonates, or by releasing young snakes produced through a conservation breeding program. Results suggested that augmenting the population would help keep subpopulations from becoming extirpated, however, the benefit would not persist once human intervention stopped unless underlying threats such as road mortality were abated.

Over the course of a three-day workshop hosted by African Lion Safari in Cambridge, Ontario, from November 11th to 13th, species experts, local knowledge holders and Gray Ratsnake supporters worked together to develop an action plan through which collaborative efforts could reverse the current trajectory of Gray Ratsnake in Carolinian Canada. Linking action planning to an updated threat assessment for the species and new information on habitat and populations, participants identified where and how to most effectively intervene, detailed what actions will be needed to achieve successful interventions and began assigning roles and responsibilities. A Recovery Implementation Group was established that will provide support and governance in the coming years. The event was sponsored by the Leeds-Grenville Stewardship Council, NRSI, and African Lion Safari, with tech equipment provided by the Canadian Herpetology Society. Dr. Phil Miller, Director of Single Species Conservation Planning at CSPG, supported the development of the PVA and workshop. We are excited to see the results of our work in a Conservation Action Plan in early 2026! Thank you to everyone who contributed their time to this project.

We would love to hear your feedback, and if you are interested in getting involved, please reach out to Heather Fotherby, Ryan Wolfe, or Ginger Elliott.