Ontario is home to a wide variety of amazing plants and animals, each with unique behavior and life histories (timeline of reproduction and lifespan, essentially, the life cycle). For years, ecologists have been fascinated by diversity all over the world, and here in Ontario is no different! As a global loss of biodiversity continues, scientists are eager to understand each unique behavior and adaptation in an effort to help protect all species. One group of animals of particular concern and fascination is turtles. Turtles are as unique in their life histories and reproductive cycles as they are morphologically (how they are shaped). Though the eight native species found here in Ontario face similar challenges, they have slight differences when it comes to their life cycles. Distinctions exist between species from the time they mate, to the time their hatchlings leave the nest.
In Ontario, the reproductive cycle of turtles pauses during the winter months, as turtles overwinter (or brumate) during periods of cold weather. When they emerge from their state of inactivity in the spring, a season of mating begins which can be ongoing through the fall. The females of some species begin nesting in late spring, while others lay their eggs during the early summer. Most hatchlings emerge from their nests during the fall, but some species are known to overwinter in their nests instead.
Mating is typically observed throughout the active season (early spring to late fall) (Bulte et al., 2021; COSEWIC, 2004-2018; ECCC, 2016). Peaks in this activity are most common after emergence from overwintering sites in the spring and in the fall before entering brumation (period of inactivity). Fall matings may be completed out of convenience, as turtles may congregate at overwintering grounds, providing ample opportunity to find a mate. These fall matings are possible because females are capable of storing sperm in their bodies for long periods of time for later use, so they can store the sperm over the winter for use the following spring. Male turtles may use different courtship tactics to gain access to females during this time, such as titillation in Painted Turtles; This courtship activity involves the use of his long claws to stroke the female’s head and/or eyes.
In Ontario, female turtles commonly reach sexual maturity, the stage in their life when egg production begins, around 10 years of age. However, other species may need to wait longer, for example, Blanding’s Turtles reach maturity much later, at 20-25 years of age. Snapping Turtles also take a long time to mature, living 17-19 years before entering this life stage (COSEWIC, 2016a, ECCC 2016).
Once a female has achieved reproductive maturity, she is now able to mate with males to produce offspring. Before nesting, some species, such as Painted Turtles, may spend more time basking to assist with egg development. Basking is a method that turtles use to regulate their body temperature and ultimately fine-tune the rate of physiological processes. This is accomplished through energy acquisition, the energy is then used by the individual to complete processes such as egg development ( Jain‐Schlaepfer et al., 2017; Topping & Valenzuela, 2021, Carrière et al., 2008; Krawchuk & Brooks, 1998). When egg development is complete, females begin the nesting process. Between late May and early July all female turtles carrying fertilized eggs will complete nesting. Certain species, such as the Musk, Northern Map, and Spotted Turtles, do not follow this timeline exactly and are known to wait until June to begin this process (COSEWIC, 2004, 2012a, 2012b). Snapping Turtles, on the other hand, tend to finish depositing their eggs in June, earlier than most other species (ECCC, 2016).
Huge variation is observed when studying the average number of eggs found in each respective species’ nest. Each nest produced by an individual female is referred to as a clutch. Clutch sizes of Ontario turtles typically range from as little as 5 to as many as 20 eggs. Snappers are again an exception to this pattern, with the incredible ability to produce as many as 109 eggs in a single clutch (ECCC 2016)! On the other hand, Musk turtles are known to produce very small numbers of eggs in a clutch, ranging from 3 to 7 eggs total (COSEWIC, 2012a).
Egg production takes place once a season for most species of turtle in Ontario, but a few species are physiologically able to produce two clutches of eggs in a given year. These species include Midland & Western Painted, Northern Map, and Spiny Softshell Turtles (COSEWIC, 2006; 2012b; 2016b; 2018b). Unfortunately for declining turtle species, some females are not able to mate and then nest annually. Instead, such as in the case of Blanding’s Turtles, some females may only nest once every three years (COSEWIC, 2016a). This is of concern for species with declining populations, as limited nesting in turn limits the number of offspring introduced to the population.
Nesting Blanding’s Turtle - The Land Between
Once eggs have been laid, the turtle offspring undergo a period of development in the nest termed incubation. Each species typically requires at least 2 months, and up to 90 days of incubation before the eggs begin to hatch, however, there are some exceptions. Blanding’s Turtles and Wood Turtles have the greatest ranges of incubation time, with 56-133 days and 65-116 days, respectively (COSEWIC, 2016a; Walde et al., 2007). Spotted Turtles require the longest time for development in the nest, with no less than 80 days of incubation before hatching (COSEWIC, 2004).
Most turtle species, including some of Ontario’s turtles display temperature dependent sex determination. This is the process whereby the sex of the offspring inside the egg is determined entirely by the temperature of the nest during the incubation process. There is no genetic designation involved (Crews et al., 1994). These species include; Northern Map, Painted, Snapping, Blanding’s, Spotted, and Musk Turtles (COSEWIC 2004-2018b; ECCC 2016). The sex of Spiny Softshell and Wood turtle hatchlings is determined through genetics (COSEWIC, 2016b; COSEWIC, 2018a). Genetic sex determination is the same process seen in humans, where sex is decided based on parental chromosome inheritance.
The majority of hatchlings begin emerging from their nests early in August, and some stragglers may still be observed leaving the nest as late as October. Interestingly, Painted and Northern Map Turtle hatchlings may overwinter in their nests and instead emerge the following year. These hatchlings still hatch from their eggs in the fall but remain in the nest cavity through the winter and emerge the following spring.
As we learn about the differences in reproductive timing between species of Ontario turtles, we are reminded of the immense biodiversity here in Ontario. Reproductive differences can even be seen within individuals of the same species. Understanding these reproductive differences is important to inform best management practices. Intraspecies differences occur throughout species’ ranges and this is why local studies are necessary.
Management practices for turtle population conservation may include installation of turtle crossing signs with special emphasis on the active season for turtles. These signs remind the public to be aware of turtles on the road, and to reduce mortality to nesting turtles and hatchlings. As scientists begin to uncover the differences between the reproductive behaviors of different species of Ontario turtles, they also begin to understand the impact the loss of one adult turtle can have on a population. This can be detrimental as the loss of one adult causes a cascade of reproductive loss through the population for years to come, as turtles take many years to reach reproductive maturity and as the rate of recruitment (the rate at which turtles replace themselves) is also very low as many eggs and related hatchlings will not reach adulthood).
Research by: Kiara Duval & Andrea O’Halloran
Written by: Andrea O’Halloran (March 2022) Edited by MaryEllen Abberger and Leora Berman
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Trials and Innovations -Testing Turtle Tunnels in The Land Between