By Carissa Stauffer, Adopt-A-Pond Outreach Technician, Toronto Zoo
Why did the turtle cross the road? To build her nest, of course!
Ontario’s turtles are seasonal species, with their active season typically lasting from April to October. During this time, they have been found to be most active during the months of May and June, where they search far and wide for suitable habitats to build their nests. This nesting quest can take these turtles through wetlands, streams, along shorelines, and most dangerously – across roadways. Unfortunately for our native turtle species, this has become one of the most common causes of turtle mortality. So, as we continue through another busy nesting season, let’s learn about what goes on during this turtle quest and how we can protect these turtle-y awesome species!
Turning Up the Temperature On Turtle Eggs
Did you know that the sex of a turtle can be determined based on where a female turtle lays her eggs? All of the species in Ontario, except the eastern spiny softshell turtle and wood turtle, have temperature dependent sex determination. This means that at a key point in egg development, the temperature of the nest determines if it will be a male or a female! For each species in Ontario, this temperature range varies slightly, but generally temperatures below 25°C produce males, temperatures above 28°C produce females, and temperatures in between will produce mixed male and female clutches. Most females when searching for a nest will choose a warmer nest site to increase the chance of a mixed clutch.
An interesting finding of climate change impacts on other turtles in Canada relates to our Ontario species temperature dependent nests. Along the coast, scientists have begun to study the impact of climate change on leatherback sea turtles. Studies are finding that the increasing average temperature is resulting in warmer nests, and thus producing more female dominated clutches. This could result in the feminization of an entire species if nests continue to remain at higher temperatures. Although this has not been studied quite yet in Ontario’s turtle species, it is a very interesting study looking at the importance of turtle nest temperatures.
Finding the Perfect Site
Turtles are picky when it comes to selecting a nesting site. It can’t be too hot, too cold, too wet, or too dry. When turtles are looking for an ideal nesting site, there are a combination of factors that they seek out.
One of the first things a turtle looks for when searching for a nesting site is the type of vegetation and canopy cover. It has been shown that sites with an abundance of surrounding vegetation and canopy cover have a negative effect on egg development because the increased shade can drop the nests temperature. If a nest’s temperature drops too low, it can cause developmental failure, and can even prolong development long enough that they don’t hatch before the fall. This means that turtles are looking for predominantly open, and exposed sites with minimal vegetation cover. Not all vegetation is bad though! Having grasses and other low vegetation nearby can help increase hatchling survival and can be identified as another desirable site feature.
Another site characteristic that turtles look at is substrate composition. Substrates (often referred to as soil) that are well-drained and loose are ideal for turtle nests since they promote the movement of airflow and moisture, while also making it easier for nesting turtles to dig. As mentioned previously, this is where turtles can be picky when selecting a site. It has been found that granular silt loam soils and sand-gravel mixes are the best substrates for turtles to build their nests in. This is because these substrates fall in between the ideal moisture and temperature ranges, where they are not too hot, not too cold, not too wet, and not too dry. You could think of these substrates as Goldilocks substrates, they are just right!
Watching Turtles During Nesting Season
Finding the ideal vegetation and canopy cover, substrate, and resulting nest moisture and temperatures often leaves turtle nests on beaches and roadsides. With these sites often resulting in turtles crossing our paths, we have created a Nesting Season Guide below to help keep you and Ontario’s turtles safe this season!
With your help, we can keep turtles and their nests safe this season and be able to see more of these cute hatchlings later this summer!
To continue learning about Ontario’s turtle species, please be sure to follow our Adopt-A-Pond Facebook page: (https://www.facebook.com/Adopt.A.Pond/ )
To learn more about Adopt-A-Pond's Community Science programs and other turtle initiatives, check out: ( https://www.torontozoo.com/AdoptAPond)
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