By David Hawke -- Have you been catching a few rays? Soaking up the sunlight? If so, it could be said that you are turning turtle. Basking in the sunlight is a pastime enjoyed by many of us, but for turtles it can be the balance between life or death.
Ontario is home to eight species of turtles, some fairly common and a couple quite rare. Each is considered a Species at Risk (SAR), ranked from species of concern all the way up to endangered. Despite having a wide range of habitat requirements between them, they all share one trait… they love to bask in the sunlight.
The reason turtles will line up on a log or pile up on an exposed rock is that they are “cold-blooded,” better defined in science as being ectothermic (ecto means outside and therm means heat). Compare that to us humans, who are endothermic (endo means inside and therm still means heat).
So, while our endothermic metabolism keeps our body at a somewhat constant warm temperature, ectothermic critters like turtles have to rely on their surrounding or outside environment (water or air) to warm them up or cool them down. (Ten bonus marks if you can recite this paragraph by memory to a family member!)
So, here is how a turtle’s day unfolds: it has spent the night in the water of a nice and deep beaver pond. Got a little chilly last night as the thermometer went down to the low double digits. When the water is cold, turtles find it difficult to move around with any agility. So, they have to warm up the ol’ bod to get ready for the day, and this is done by hauling themselves up and out of the water, and onto a floating log or rock. (This is you, in the car, lined up at the coffee shop… awake, but not really.)
They are now trying to capture some of the warmer air temperature so that they can crawl and swim like the aquatic beasts they are. Some species bask more readily than others: painted turtles, Blanding’s turtles and map turtles are renowned for their basking, with many individuals lining up along the log. Others, like snapping turtles and musk turtles, may just float at the surface to get their morning dose of warm sunshine.
Depending on the temperature variation between water and air, basking may take place for just a couple hours or as long as eight hours. Turtles actually need to dry off, thus killing some of the fungal growth on their shells, as well as encouraging attached leeches to drop off and get back into the water.
The Ultra Violet B (UVB) radiation actually assists with the production of Vitamin D3, which in turns helps with calcium retention, which makes for solid shells and good bones. It does a turtle no good to skulk in the shadows all day.
If you should be able to get close enough to a gang of basking turtles you may see that many will have stretched their legs and feet out to the side to catch as much solar radiation as possible. By constricting their blood flow just beneath the skin, the pooling blood gets a few extra moments of heating. When the muscles are relaxed a flush of the warmed blood flows into the body while cooler blood is now forced into the legs where it will, in turn, be constricted and warmed up.
Once optimum internal temperature is reached, the turtle slides off the log and into the water, ready to forage for plant roots and crunchy critters. If the water has cooled significantly the turtle may re-emerge for another round of basking so as to warm up again.
When the shortened days of autumn arrive and there are fewer opportunities to warm up, turtles take that as a sign that hibernation draws nigh. But I’m getting ahead of myself… let’s all enjoy summer while it’s here… if only for a couple more weeks.
Dave’s Notebook: Looks like a few more hot and humid summer days are coming our way. Time to make like a turtle and balance your days between some serious basking and a cool swim.
© 2020 David J. Hawke