Turtles of Wisconsin
Turtle Eggs
Turtles like this common map turtle, use their
egg tooth to cut through the tough outer shell
in order to hatch. Can you spot the egg tooth?
All turtles lay their eggs on land, most in a nest that they dig. Most nest once a year, but some painted turtles and map turtles may nest twice in the same season. Nesting usually occurs around or after dusk, but it may also happen near dawn or even occasionally during the day. Smaller turtle species lay about 3-5 eggs while larger turtles like the snapping turtles lay from 30-80 eggs. Once the eggs are laid, the female turtle leaves them to hatch on their own. Turtle eggs are often uncovered and eaten by foxes, raccoons and skunks.
Eggs incubate from 60 to 90 days in Wisconsin, depending on the species. During a cool summer, it might take even longer. Some eggs laid late in the season may not hatch until the following spring. Those that hatch in early fall, will overwinter in the nest. A glycol-like antifreeze keeps the eggs or hatchlings from freezing during the winter. But, if the winter is very dry or cold with little snow cover, many of the eggs and hatchlings will die.
Fun Fact. Here's an interesting tidbit about turtles. The incubation temperature of eggs determines the sex of turtles in most Wisconsin species including Blanding's, maps, painted, ornate box, and snapping turtles. For these species of turtles, nests produce more females at high incubation temperatures and more males at lower temperatures.
Compared to other animals, turtles are very slow to mature. Female Blanding's turtles may take from 17-20 years to reach sexual maturity. But, since turtles are generally long-lived creatures, this hasn't been a problem. The fact that turtles can live and reproduce for many decades is probably why they have survived for so long. But, recently, human activities have increased the death of adult turtles. Many turtles are killed by cars as they cross roads. Also, our elimination of large predators has allowed medium-sized predators to increase. These medium-sized predators like foxes, raccoons, and skunks have increased the predation on turtles nests. We'll have to keep a close eye on turtle populations.
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