by Carl Strang
There are many sorts of comparisons that can be made between our region at the southern end of Lake Michigan and other parts of the world. Today’s focus is on a puzzling absence. I loved turtles as a child, and enjoyed encountering eastern box turtles and ornate box turtles in the woodlands of north central Indiana where I grew up.
When I lived in south central Pennsylvania I got the opportunity to conduct an ecological study of eastern box turtles and wood turtles, whose ecological differences I summarized in an earlier post.
When I moved to northeast Illinois, I was disappointed and somewhat puzzled to learn that none of these three semi-terrestrial species lives here. After pondering this absence off and on for some years, I feel ready to pose a hypothesis. In the case of the box turtles, I think it has to do with our soil. Box turtles bury themselves in upland places to hibernate for the winter.
Our northeast Illinois soil is derived from a clay parent material, ground up New Albany shale which the Lake Michigan lobe of the last continental glacier left behind as part of its legacy. Bricks are made of clay. It’s a difficult material to dig in, whether for gardening or for hibernating, and I suspect this is what is blockading the eastern box turtles, which live east and south of us, and the ornate box turtles, which live west and south of us.
As for the lack of wood turtles, that is perhaps a simpler puzzle to solve. Wood turtles live in forests, and our region historically was prairie punctuated by more open, drier woodlands. Here the wood turtles appear to be replaced by Blanding’s turtles, which live in prairies and their adjacent wetlands in much the same way that wood turtles made their living in the lowland eastern forests, spending some of their time (and hibernating) in the marshes, ponds and streams, but emerging frequently to forage on drier prairie land. Perhaps I am influenced by my childhood experience here as well. Most of our local landscape in Indiana historically was a mix of prairie and dry to mesic woodlands on sandy soil. We had eastern box turtles, ornate box turtles, and Blanding’s turtles, but no wood turtles.