Turtles in winter!

By Steve Blight

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As the seasons continue their inevitable progression into winter, animals that don’t migrate prepare to survive the cold season in a host of different ways. Some cut wood and dig out their dormant snowblowers. Others, like turtles, make serious lifestyle changes.

Turtles are fascinating reptiles that in some respects haven’t changed for a very long time. It is believed that the basic form of a shell first evolved some 225 million years ago and hasn’t changed very much since – perhaps supporting the old adage “if it ain’t broke, don’t fix it”.

How do turtles spend the long northern winter? Like most schoolchildren I was taught that turtles bury themselves in the mud at the bottom of lakes and ponds. I have long wondered if the story is as simple as I was taught, and if it is, how do air-breathing creatures spend 6 months in waterlogged mud and live to tell the story?

It turns out that the first part is mostly true – many turtles found in our area do indeed head to the bottom of ponds and lakes to pass the winter. Here is a brief run-down of the wintering habits of seven turtles that are found in Eastern Ontario.

• Snapping Turtles hibernate from mid-October to early April in shallow water in the bottom mud, under submerged debris, or sitting quietly on the bottom.

• Painted Turtles spend from late October to early April in quiet permanent water bodies where they burrow into mud on the bottom.

• Blanding’s Turtles hibernate under water or under debris near water from late October - early November to early April.

• Map Turtles spend from early November to early April in large water bodies, wedged under submerged logs, partially buried in bottom mud, or in muskrat burrows.

• Common Musk Turtles are dormant from mid-October to early April, burrowing into bottom mud or beneath logs, overhanging banks or muskrat houses.

• Spotted turtles hibernate in shallow water from mid-October to late March.

• Wood Turtles spend the period from mid-October to mid-April unburied on the bottom of streams or wedged under a submerged rock or log.

Curiously, many turtles occasionally move around in winter and can be observed moving slowly under ice. Some turtles that live south of here don’t hibernate under water. For example Box Turtles, which live in the southern half of the United States, dig a deep burrow in dry soil where they spend the winter.

Now for the second question – as air-breathing animals equipped with lungs, how do they get oxygen underwater? The answer turns out to be a fascinating adaptation to our northern climate. Their cold bodies slow down markedly in winter. They stop breathing through their lungs. They don't eat and their hearts slow down to the point where they beat only once every few minutes.

Because their bodies are running at such a slow speed, they don't need much oxygen, but they do need some. Fortunately there is almost always a small amount of oxygen dissolved in water (which is how fish survive), and cold water holds more oxygen than the warmer water of summer. They get the small amount they need in winter from specialized tissues found in two places on their bodies – the throat and just inside the tail opening. These tissues have lots of minute blood vessels that permit oxygen to be extracted from the water into the turtles’ blood streams.

When the seasons turn to the warmer months, the turtles will warm up and become active. Once again, they will look for nice places to sit and enjoy the sun – just like us on a warm spring day.

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Please feel free to report any observations to Lorraine Julien at naturewatching@gmail.com  or Steve Blight at natureobservations@rogers.com