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Wisconsin Native Turtles

Freshwater Turtle

Turtles are among the most recognizable and iconic of animals. Any animal with a shell and a backbone is a turtle whether they are called turtles, tortoises, or terrapins. In fact, terrapin is an Algonquian name for turtle.

Turtles are amongst the most ancient of all the animal species on planet Earth. Turtles are believed to have originated as far back as 279 million years ago, making them a species older than even the oldest dinosaurs. The effects these venerable animals have on their ecosystems are immense, and, over millions of years of evolution they have adapted to suit many different habitats and systems.

Worldwide there are 356 turtle species on all continents except for Antarctica. The US has more species than any other country with about 62 currently recognized. Unfortunately, turtles are now the most imperiled major group of vertebrates with about 60% of modern turtles already extinct or threatened.

Turtles Face Many Threats

Comparison of Turtle Size (MAX)
Eastern Spiny Softshelled Turtle
Snapping Turtle
Smooth Softshelled Turtle
Blandings Turtle
Eastern Spiny Softshelled Turtle
Common Map Turtle
Painted Turtle
Wood Turtle
False Map Turtle
Ouachita Map Turtle
Common Musk Turtle
Ornate Box Turtle

The fact that freshwater turtles need both terrestrial and aquatic habitats to survive makes their conservation relatively complex, since many types of habitats need to be protected for a single species. The need for several types of habitats throughout the year also increases the amount of threats affecting them, since different elements can threaten them in each habitat.

Turtles are endangered or threatened due to exploitation and trade. They are also threatened by increased development and habitat loss. Turtles are traded primarily for the pet trade, food consumption or traditional medicines.

Ecological Importance of Turtles

Turtles play important ecological roles in their environments that are diminished as their populations decline. They play an enormous role in the function of the ecosystem, not least in seed dispersal. The turtles eat the plants and deposit the seeds in their excrement, the seeds then flower. Also, the eggs of turtles are major food sources for animals, such as rats, snakes and lizards.

Basic Turtle Anatomy

Skeleton

Graphic of turtle anatomy

The anatomy of the sea turtle is unique in that it is one of the few creatures to have both an internal and external skeleton. The main purpose of the external skeleton is to provide protection and support for internal organs. It is comprised of a bony shell which is, itself, divided into two halves: the lower plastron and the upper carapace. The carapace is actually the broadened, fused ribs of the turtle and is covered by a series of firm but pliant structures called scutes.

The internal skeleton provides an anchor for the turtles’ muscles. The spine is fused to the carapace. The long digits in the limbs of the turtle are fused together to form the flipper.

Flippers

The flippers themselves are large and sensitive to touch. The front flippers propel the turtles through the water as they’re moved in a figure-eight pattern. The rear flippers act as rudders, providing both direction and stability to the turtles’ motion. They are also used by females to dig the egg cavity during nesting.

Mouths

The mouths of sea turtles contain no teeth. Instead, they are sharp and beak-like and are well-suited for crushing or tearing their food.

Vision

Turtle Eye

The eyes of sea turtles provide them with good underwater vision, but are less useful above the water’s surface where they give the turtle a near-sighted view of the world. There is a gland near the eye that releases excess salt and fluids in order to keep the eyes moist when females are on land. These glands are responsible for the tears a turtle sheds while laying its nest.

Tail

In most respects, the males and females of the various turtle species have few physical differences on the outside. One obvious distinction is the size of their tails. Female’s tails are short and do not extend beyond the hind flippers. However, the tails of the males are considerably larger and usually extend well past the hind limbs. Additionally, only the female has an ovipositor, the structure used to deposit her burden of eggs.

Reproduction

Breeding begins at sexual maturity. In most species, this process starts as soon as spring arrives, and the courtship between males and females can happen at any time until the fall. Mating occurs underwater, and the eggs contained within the females are then fertilized. In some species, females can store sperm from a given male to fertilize later clutches, sometimes years after the fact! Females of several freshwater turtle species have also been known to be able to produce clutches fathered by several different males at the same time.

Snapping Turtle, Chelydra serpentina, Mating

When they are ready to lay their eggs, females dig their nests in the sand or the earth near their aquatic habitats. The number of eggs produced varies enormously by turtle species. Eggs are then laid, and are often covered by the female using her hind legs. The temperature in the nest during the incubation which determines whether a hatchling will be male or female. Higher temperatures will cause for more females to be born, and lower incubation temperatures, more males.

The female leaves the nest after having laid the eggs and the hatchlings are born with no parental care. Following their birth, the hatchlings from most species will instinctively go to the water, where they can more easily hide from predators. Painted Turtle and the Map Turtle hatchlings may be born in the fall, which means that these hatchlings remain in the nest until the following spring. They can survive throughout the winter at temperatures as low as -10°C with the help of antifreeze chemicals which they produce in order for their cells to remain unfrozen and undamaged. They can only do so during their first winter, following which they must head to the water.

Habitat and Behavior

Baby Eastern Spiny Softshell Turtle, Apalone spinifera

Turtles become active in the spring when water and air temperatures go above 60 to68° F. During its activity period, a typical freshwater turtle’s day is divided between resting, basking and foraging. Basking is the behaviour that turtles, and other reptiles, exhibit when they are resting in the sun, either out of the water or just at the surface. This helps regulate their bodies’ temperature (as they are ectothermic), is beneficial to their skin and shells, and speeds up their metabolism.

While most turtles are diurnal (active during the day), the Common Snapping Turtle and the Eastern Musk Turtle, or Stinkpot, may be looking for food during the night.

Even if turtles are recognized as aquatic animals, all freshwater turtles rely on land for their survival. Indeed, they all need to come out of water for greater or lesser periods of time, depending on the species. Some only come on land to lay their eggs and remain in water for the rest of the year. This is the case for the Eastern Musk Turtle and the Common Snapping Turtle. The Spiny Softshell, which is also well adapted to aquatic life, can even absorb oxygen dissolved in the water through its skin! Others, like the Painted Turtle and the Map Turtle will come out on logs or rocks daily in the summertime to bask. But some species, even if they do still need access to water for periods of their life cycle, can spend a larger period of their time on land.

Box Turtle Laying Eggs

This is the case of the Wood Turtle, which inhabits woodlands, farmlands and grasslands not too far from water for much of its activity period. This species is considered the most terrestrial of our turtles, but the Blanding’s Turtle and the Spotted Turtle may also be observed wandering out of the water, close to the shoreline, especially in the spring. The Blanding’s turtle may even travel long distances on land to go from a wetland to another, or to reach their nesting site.

During the winter, when temperatures get too cold to sustain their metabolisms, all freshwater turtles head underwater to hibernate. They typically bury themselves in the substrate, or the sand, mud or pebbles found at the bottom of their aquatic habitat, under the ice, as they cannot survive being completely frozen. They remain dormant, slowing their metabolism down in order to conserve energy and use as little oxygen as possible.

The Common Snapping Turtle can survive the winter months completely covered in mud with very little available oxygen in the water.

Further Reading:

 Beavers — Nature's Hydrologist, Part 2
 Garter Snakes — The Gardener's Friend
 Wisconsin Native Salamanders
 Goundhog or Woochuck: All The Facts
 Voles, Both The Good and The Bad

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