Turtles in High Park – Part B

Its Shell is a Body Part, Not a House

The turtle’s shell is part of its skeleton, not an accessory it carries around. It cannot leave it behind or live without it. All turtles have a top shell and a bottom shell that continue to grow with the turtle. The shell is made of bony plates covered in layers of large thick scales, and yet a turtle can actually feel when its shell is touched. The shell contains nerve endings and bleeds if damaged. Aquatic turtles, like the turtles in High Park, annually shed the outer layer of their shells to lighten their load.

To protect themselves on land, the red-eared sliders and the Midland painted turtles can pull their heads and legs completely inside their shells. Not so, the snapping turtle whose bottom shell is too small to accommodate its retracted limbs and head. Thus, it cannot find protection in the usual way of turtles. This defencelessness on land helps explain the cantankerous disposition of the snapping turtle out of water.

Winter Takes Their Breath Away

Throughout the ice-free months of the year, the turtles come to the water’s surface for air. They exchange oxygen and carbon dioxide just as we do through nostrils and lungs. But in the winter when trapped beneath the ice, they cannot come up for air for months at a time. How is it possible to survive so long without breathing? Two super powers are behind this feat.

First, turtles can survive on very little oxygen when it’s cold. A turtle cannot produce its own heat like mammals do. Its temperature always matches the temperature of its surroundings. When the water beneath the ice is barely above freezing, the turtle’s temperature is likewise barely above freezing. Although most turtles cannot survive temperatures below freezing, they can live in pond water at temperatures just above freezing. To survive the winter, the turtles in High Park stay under water below the ice, drastically dropping their rate of metabolism so almost no oxygen is needed.

Second, what minimal oxygen turtles do require they can absorb through certain areas of skin especially rich with blood vessels. On Midland painted turtles and red-eared sliders, this special skin is located under their tails, earning them the nickname “butt-breathers.” Snapping turtles get oxygen through skin in their mouths and throats by periodically extending their heads from the mud or silt where they like to bury themselves in winter.

High Park’s two native turtles (snapping turtles and Midland painted turtles) can endure this state of oxygen deprivation for over 100 days if need be. But such long periods with low oxygen take a toll: acid accumulated in the body’s tissues makes its muscles severely cramped when the turtle is finally able to come up from under the ice.

Coming Up to Speed

It’s easy to spot red-eared sliders and Midland painted turtles when the weather warms up. They crawl out of the cold water onto a sunny spot where they will bask for five or six hours to warm up their chilled and sluggish muscles. If they run out of room on a log, they climb on top of each other to get in the sun. When the stack gets too much for the bottom turtle, it raises its back legs and rocks the top turtle off the pile.

Snapping turtles are not routine baskers so we see them less often. To raise their body temperatures, they stay motionless in shallow water or float on the surface.

Good Sense

Turtles rely most on sight, smell and hearing to interpret their surroundings. Good colour vision and a keen sense of smell help them locate food. Not only is a turtle able to smell and taste its food, but a Jacobson’s organ in the roof of its mouth enables it to taste and smell the air too. This helps male and female turtles find each other for mating. They can even smell underwater! Turtles have round eardrums just beneath the skin on the sides of their heads. These enable the turtle to feel vibrations and hear low sounds.

S L O W Describes the Turtle to a T

The turtle’s reputation for being slow is legendary and not just limited to its pace of movement either. After their first year, they grow very slowly, averaging little more than a few centimetres annually. And it takes a long time for a turtle to reach breeding age, up to a third of its full lifespan.

The growth of turtle populations is also incredibly slow. Only 1% of hatchlings survive to breeding age. It may take an egg-laying female her whole life just to replace herself. Turtles that do survive can live a very long time. Midland painted turtles live up to 60 years and snapping turtles up to 70 years or more. One snapping turtle found in Algonquin Park was over 100 years old! Red-eared sliders live 20 to 30 years when kept as pets, but their lifespan outdoors in Ontario is not known.

Valuable Wetland Janitors

Turtles are aquatic scavengers and play a key role in keeping our wetlands clean. About 90% of their diet is made up of dead animals and plant matter. Turtles are toothless omnivorous and opportunistic feeders. When they are young, their diets are richer in animal protein and calcium to maintain shell growth.

Not only can aquatic turtles go a long time without breathing, they can also go a long time without eating. They might be slow, but boy can they fast! They stop eating once the water temperature falls below 15C and can fast for months until it warms up again.

Testing Turtle Nesting

Turtles mate from April to November. A single mating event enables the female to store sperm and lay eggs for several seasons. In May or June, when ready to lay her eggs, she looks for well-drained sandy soil in a sunny spot with little or no vegetation, often returning to the same nesting site year after year. The female usually lays her eggs within a few hundred metres of water. However, to find the right nesting site, she may travel quite a distance, sometimes even a few kilometres. Traveling to the nest site is the first survival risk for both the mother and her eggs. A slow moving turtle on a busy road is in great peril of elimination.

When she finds the site, the turtle sometimes urinates on the soil to make excavating easier. Using her back legs, she digs a hole and guides the eggs into it as she pushes each one out. It can take many hours to dig and deposit the eggs into the hole before she backfills to cover them. She might urinate again to create mud for closing the opening.

Don’t Even Count Your Eggs Until They…Become Adults

The survival rate of adult turtles can be pretty good, but reaching that age is filled with so many hazards that it is difficult for turtles to live long enough to reproduce. The first 24 hours in the nest pose the greatest survival risk. Many animals can smell the freshly laid eggs and waste no time raiding the nest. Dense human settlement around High Park has led to unnaturally high populations of raccoons, skunks, foxes, gulls and crows, all turtle egg connoisseurs.

If the eggs escape all predators, they hatch between late August and late October. The cooler the temperature, the longer they incubate. The nest temperature also determines whether turtles will hatch as males or females: between 23C to 28C eggs hatch as males, and above and below that range, as females. Fluctuating temperatures produce a nest of both sexes.

It can take up to three exhausting days for the loonie-sized turtle hatchlings to break through their shells using their sharp temporary egg tooth. The journey to water (in fall for snappers and spring for Midlands) may include roads, insurmountable curbs and a host of predators. In addition to the original nest predators, the hatchlings may then also be threatened by coyotes, herons, egrets, hawks, owls, bullfrogs and large fish.