Every year, thousands of reptiles in Ontario never make it across the road. For some species, a single stretch of pavement can mean the difference between survival and local extinction.
Reptiles are especially vulnerable to the threat of road mortality because they take many years to reach sexual maturity and have few offspring that survive to adulthood. This means that even the loss of a single reproductive adult can have serious impacts on a population.
Georgian Bay’s mild climate and diverse habitats support a high diversity of reptiles compared to other areas in Ontario. Unfortunately, the area is no stranger to road mortality. Thirteen of the 19 reptile species found along eastern Georgian Bay are considered at-risk, and all face the threat of road mortality.
Road mortality mitigation is not one-size-fits-all. Researchers, non-profit organizations, municipal governments, landowners, and First Nations have been teaming up to develop, implement, and test new ways to mitigate reptile road mortality.
Opportunity for Innovation
In 2022, the Georgian Bay Mnidoo Gamii Biosphere (GBB) partnered with the Township of Carling to pilot an innovative fence design for mitigating reptile road mortality as part of the Maamwi Anjiakizwin (MA) initiative.
A causeway built directly through a Provincially Significant Wetland, unsurprisingly, was a hotspot for reptile road mortality. The wetland provides critical habitat for several species-at-risk, including the Blanding’s turtle, massasauga rattlesnake, and eastern foxsnake. The eastern foxsnake was of particular concern because the species is notorious for using their strong climbing abilities to climb over other types of barrier fences.
With input from MA partners, the following design criteria were identified:
- It does not impede road maintenance (e.g., mowing, plowing) or create a barrier to accessing traditional lands;
- It must prevent climbing by large reptiles such as eastern foxsnakes; and
- Animals must be able to safely access habitat on the opposite side of the road.
GBB and the Township of Carling decided on a curved (concave) fence design, building off of the work of Heaven et al. in 2019. The design uses HDPE culverts, a commonly used material in road construction, cut lengthwise and installed at-grade with the road. Provincial guidelines state that fencing for foxsnakes must be a minimum of 2 meters in height, with an overhang. However, a smooth, concave fence design might pose a greater challenge to climbing foxsnakes and therefore allow for a shorter fence height (i.e., less than the recommended 2 meters).
Barrier fences are designed to keep animals off the road, but in doing so they also restrict animal movement between habitats. Therefore, they often incorporate crossing structures (i.e., “ecopassages”), such as overpasses or underpasses, which allow for safe animal crossings. For this project, the mitigation design utilized three pre-existing drainage culverts to serve as aquatic ecopassages, plus the construction of an additional terrestrial ecopassage.
The end result was 400 m of concave barrier fencing coupled with four below-road ecopassages. The concave barrier fence was designed to prevent animals from climbing over the fencing, while the at-grade design does not impede road maintenance or limit access to traditional lands.
To study the effectiveness of the design, project partners collaborated with Dr. Jackie Litzgus and graduate student, Sabrina Lounsbury, from Laurentian University.
Research and Monitoring
Pilot projects allow researchers to test and refine conservation strategies on a small scale, assessing effectiveness and identifying challenges before full implementation. This approach minimizes risks and ensures efficient resource allocation for evidence-based decision-making.
The goals of the effectiveness study were to determine whether:
- The mitigation resulted in a reduction in the number of reptiles found on the road;
- Reptiles were utilizing the drainage culverts to safely cross under the road; and
- The design prevents eastern foxsnakes from climbing over the mitigation.
To address these research goals, researchers used a combination of road surveys, wildlife cameras, turtle live-trapping, and snake behavioural trials.
Road Surveys
While road survey data showed a 26% decrease in the number of reptiles found on the road post-construction, reptiles were still finding ways to access the roadway. Hotspots were found to have moved to the fence ends, which reptiles travelled around to gain access to the road. This is important information to come out of the pilot project and indicates that in order to improve the effectiveness of the mitigation design, the overall length of the barrier fence should be increased. This is a lesson that can be implemented in future mitigation designs.
Ecopassages
Wildlife cameras were installed at the entrance of each end of the ecopassages, programmed to take a photo every 30 seconds for two summers post-construction. The end result was a compilation of over 6 million photos which revealed a total of 2,371 reptile crossings from 13 species. This is the highest known number of reptiles recorded using ecopassages in Ontario and demonstrates that the drainage culverts were highly successful as ecopassages for reptiles.
Turtle Live-Trapping
Utilizing live-trapping, researchers estimated the population size of three turtle species living in the wetland adjacent to the mitigation. They found that the species composition of turtles in the wetland was similar to the species composition of turtles in the ecopassages, indicating that the turtle community was readily using the ecopassages.
Behavioural Trials
The concave barrier wall was effective at preventing all tested foxsnakes from climbing. Therefore, it can be assumed that a concave fence design would be effective at preventing other non-climbing reptiles, small mammals, and most amphibians from accessing roadways. However, a single, large foxsnake was able to climb over the mitigation using the supporting rebar. This individual was the largest snake in the study, reaching nearly 1.5 m in length and weighing over 1 kg. Foxsnakes in eastern Georgian Bay can reach up to a maximum of 1.8 m in length and weigh up to 1.5 kg. This important observation can inform future fence designs by increasing the length of the overhang above the rebar to prevent large snakes from climbing over.
Looking to the Future
The pilot project demonstrated the strong potential of this mitigation design for preventing reptile road mortality and highlighted key lessons learned to further improve the design. Modifications such as expanding the overall length of the mitigation and creating a larger fence overhang will greatly improve the effectiveness of this design. In addition, on-going site monitoring, including monitoring the structural integrity of the fence, will provide valuable insights into the long-term durability of the design.
This project represents a successful collaboration between academia, non-profit organizations, First Nations, municipalities, and landowners. GBB commends the Township of Carling for supporting this pilot project aimed at reducing threats to species at risk. Lessons learned from this pilot project are being shared with others working to make roads safer for wildlife across the region and internationally, helping to fill knowledge gaps and improve conservation strategies using evidence-based decision making.
