As humans continue to build infrastructure through natural landscapes and wetlands, negative impacts on biodiversity increase. Biodiversity refers to the variety of life on Earth seen in the many different plants and animals. With development, habitat removal and fragmentation, and other huge environmental changes we are experiencing a rapid drop in species numbers and population sizes all over the world. Here in Ontario the situation is no different. Over the years many animals native to Ontario have become classified as “at-risk” of extinction. A significant contribution to loss of biodiversity includes roads and related traffic, which causes injury and often death to animals. For the eight species of Ontario turtles, this happens much too frequently and according to scientific studies, this will have lasting effects on population viability (2). In an attempt to reduce the frequency of turtle injuries inflicted by cars many strategies to mitigate collisions have been developed, and some have been implemented in areas with frequent turtle sightings and high mortality rates. These strategies have been designed to allow passage of turtles through developed landscapes to access other parts of their home ranges (4).
One of these strategies is called the ecopassage, which is a man-made tunnel that passes under high-ways or country roads to let small animals cross safely (6). This infrastructure provides safe routes between the various and also essential parts of a turtle’s home range. To help guide the turtles towards the ecopassages, researchers also installed exclusion fences. These fences not only direct turtles to the safe zone, but they act as a barrier between the edge of a turtle’s habitat (most often wetlands) and the dangerous roads. These fences are essential in preventing turtles and other small animals from wandering onto the road meanwhile ensuring they find the tunnel (4). This strategy has proven successful for all targeted reptile groups except for snakes as they can easily maneuver themselves through the small gaps in a fence (2). While good for turtles, the fencing can harm snakes if not constructed with them in mind: In a study conducted by Boyle and colleagues assessing the risk of desiccation associated with exclusion fencing, there were ten incidents of a snake being found trapped in the fencing either in a state of desiccation (dried out) or deceased (1). To manage this issue and prevent snakes from passing through the gaps in the fence, geotextile fencing may be added to the base of the exclusion fencing. Geotextile fencing is a type of durable felt fabric and was found to increase the rate of exclusion in smaller reptiles and amphibians, such as snakes (7). This fabric may also help turtles, because turtles are excellent climbers, and the textile may limit not only sight lines and the temptation for turtles to climb over fencing, but also their ability to scale the fence.
Studies have been conducted on the effectiveness of fencing for turtles. In particular, Read & Thompson found that turtle road mortality was significantly minimized where ecopassages were installed in Lake Simcoe. Importantly, their study found that turtles also maintained the same level of maneuverability between habitats with the addition of ecopassages, meaning the tunnels did not deter them from traveling (5). However, turtle road mortality was still happening at the end of the exclusion fence lines, indicating that further investigation and construction was required to completely eliminate road mortality. Data, and then monitoring and maintenance are therefore essential to successful ecopassages. Additionally, the effectiveness of ecopassages is short-lived unless regular yearly maintenance is conducted on the passages and fencing.
For monitoring, scientists can then observe turtles using the tunnels with the help of time-lapse and motion sensor cameras allowing them to judge how often the tunnels are used and by which turtle species (3). Additionally, routine maintenance checks will reveal damage from wear or improper installation techniques. This damage, if not fixed, may actually lead to similar or greater death rates than before the fencing installation, because animals can be trapped within broken portions of the fence and injure themselves when struggling to get free, or they could enter roadways where fencing has become compromised or is insufficient and then become trapped o fencing on the opposite side of the road. At these times animals may bounce back and forth, so that they are either injured or perish on roads (2).
Reducing turtle road mortality of turtles is essential to stop the rapidly declining populations. Moreover, the loss of turtles to vehicle incidents affects more sexually mature females (egg-layers) as they enter or cross roads to reach regular nesting sites each year. According to researchers, the loss of only one female can be detrimental to the overall viability of a turtle population, especially because of turtles’ reaching sexual maturity at late ages (taking up to 20 years before they are able to produce eggs) and the low level of annual recruitment (the relative numbers of new offspring entering the population). The death of a female means there will be a measurable drop in egg production for years to come in the population. Decreased egg production has a cascading effect through the age structure of a population and results in even lower annual recruitment of new juvenile turtles, and eventually causing a decline in the number of sexually mature turtles. This decline is hard to reverse in populations with such slow life stages, like turtles (8).
Considering the research at both ends of the spectrum, from the benefits of ecopassages, to the impacts of road mortality on populations, should be widely implemented throughout Ontario in turtle hotspot areas wherever they are feasible. These measures would drastically reduce the rate of turtle mortality and assist populations to stabilize, especially as damage caused by increased development forces turtles to cross roads more often and face increasing threats (5).
The Land Between and Turtle Guardians have installed their first turtle jump-out fencing pilot in Gooderham in fall of 2021. Click here to learn more.
Written by: Andrea O’Halloran, Communications Specialist