A gravel road, a sandy bike trail, and a garden mulch pile aren’t the most picturesque parts of the cottage landscape, but these human-made sites are prime nesting locations for turtles. A study led by University of Toronto undergraduate student Elizabeth Ann Francis examined why snapping turtles in Algonquin Park like to choose human-made (anthropogenic) nest sites.
With all eight of Ontario’s turtle species listed at risk by the Committee on the Status of Endangered Wildlife in Canada, understanding nesting patterns in human-modified landscapes is key to conservation efforts. While anthropogenic and natural sites examined in the study did not differ in aspects like distance to the nearest water, the anthropogenic sites had less ground-cover plants, greater soil brightness, and were 3.3°C warmer than natural sites.
“When we build roads, we essentially make everything a turtle could ever want,” says Patrick Moldowan, a Ph.D. candidate in the Department of Ecology & Evolutionary Biology and the School of the Environment at the University of Toronto. The attractive features include soft, sandy gravel that is easy to dig, has good drainage, and receives a lot of heat from the sun. “But it comes with some major caveats. One is contamination from road runoff—things like oil and leaching of chemicals added to the asphalt. But more acutely there’s a very high risk of road mortality, and if not for the female then certainly for her offspring if they successfully leave their nest.”
This catch-22 is why researchers suggest anthropogenic nest sites are ecological traps. Turtles are drawn to these heavily altered sites and can incur major costs by doing so. In addition to increased danger from cars and other human activities, a seemingly slight increase in nest temperature can have major consequences for hatchlings. Because turtles have temperature-dependent sex determination, nest temperature impacts whether males or females develop. “Three degrees doesn’t sound like much, but it’s enough to turn a clutch of eggs from being entirely one sex to entirely the other, or at least heavily skewing it,” says Moldowan.
Moldowan says that anthropogenic nest sites, which often consist of light-coloured substrates like crushed limestone gravel, normally would be expected to absorb less heat than the dark, organic soil of natural sites. Moldowan compares the different nest colours to parking a white car and a black car in a parking lot in the middle of summer—they’ll both be hot, but the black car much more so. Moisture retention in the soil and exposure to daylight are two possibilities for the differences in temperature between nest sites.
If you come across a turtle, laying eggs or not, while exploring Algonquin Park, you can contact the Algonquin Wildlife Research Station to report your sighting. Some turtles in the park are marked with numbers and letters, like miniature licence plates on the backs of their shells. Moldowan says if you report a turtle’s number, the researchers are happy to provide you with that turtle’s history.
Turtles of course don’t just nest in Algonquin Park. Throughout Southern Ontario, turtles are on the move on land any time from mid-April to October, with June being the peak month for nesting. Some turtles prefer to make their inland journeys in the evening, but you’re more likely to notice snapping turtles, thanks to their large size and habit of coming out in broad daylight. It can be alarming to spot a turtle marching away from a pond or wetland, but don’t worry, the turtle isn’t lost. The turtle may be travelling from one water source to another, or making the trek to a nesting site. Dr. Sue Carstairs, the executive and medical director with the Ontario Turtle Conservation Centre, says, “I always say they’ve been around 200 million years, and they haven’t been around that long by getting lost. They know where they want to go.”
If you discover a turtle digging a nest on your property, the first thing to know is that it is illegal to disturb a natural nest. That includes digging up the eggs and raising the hatchlings yourself. It is permissible to protect a nest on your own property, but it’s important to make sure it’s done properly, or more harm could be done than good. You can purchase or build a protective nest cage that will prevent predators like raccoons getting at the eggs without disturbing the temperature of the nest.
The cage must include escape routes so that the babies can leave once they hatch. Ask your local conservation group about where to purchase nest protectors, or check out the Ontario Turtle Conservation Centre website for an overview of how to build a wooden nest cage.
Dr. Carstairs says it is important for everyone to do their part to help nesting turtles, as it takes 20 years for many turtles to start reproducing and very few of the offspring survive to adulthood. “Every nest that they save, increases the chance of those babies hatching, and that increases the chance of adults coming out of them.” She adds that the Ontario Turtle Conservation Centre receives many calls from people who want to get involved with turtle nest protection. “People are getting the message and they care. Particularly cottagers care, because they want their wetlands to be healthy.”