Thursday, April 22, 2010

Brutish clam-cracker

On a recent foray into the depths of southernmost Ohio's Adams County, Randy Lakes took me to see a wooded hillside carpeted with a fantastic array of spring flora. While I was busily photographing trillium, cohosh, and other botanical gems, Randy called out "turtle!" And lo and behold, basking on a limestone slab far below the country lane that we were strolling along, was an armor-plated whopper.

We had stumbled across a Map Turtle, Graptemys geographica, lolling about in the sunshine on a rock along Ohio Brush Creek. Even though Randy and I were a good 100+ feet away and high above the river, the turtle was fully aware of us and watching warily. Knowing something about these turtles and their behavior, I advised a slow, stealthy advance in order to procure photos, the wildflowers now forgotten.

Map Turtles love to sun themselves, but usually do so right at the edge of a rock; thus they can quickly drop into the water and vanish should a threat appear. Believe it or not, I once had a job that required investigating riparian (streamside) corridors by canoe, or foot if necessary. Because of that position, I've either floated or walked a huge number of miles of Ohio's streams, and in the course of doing so caught scads of turtles of every expected species. Maps and the soft-shelled turtles are the wariest, and for the most part you won't get anywhere near them.

Map Turtle prepares to slip into the drink. These are the only photos I managed, and they were taken at full 12x zoom, and then cropped. Even so, the bold yellow blotch behind the eye is evident; a good long-distance field mark. We can also see the characteristic shape of the carapace, or upper shell, which is rather low and flat with an obvious keel down the center.

Both the common name, map, and the scientific epithet, geographica, refer to the beautifully ornamented carapace. On younger specimens or especially bright turtles, the shell is decorated with ornate lines and squiggles, resembling the elevational lines on a topographic map.

Map Turtles inhabit larger streams and rivers with a permanent flow, and sometimes lakes. They are amongst our largest turtles - a big female might exceed 10 inches in length and weigh several pounds. Although I never found them to be particularily aggressive when caught, you do want to mind the mandibles. Their jaws are VERY powerful, and the turtles are fond of snacking on clams and crayfish, which are cracked open much as you would crack a walnut.

Turtles are a fascinating part of stream life, but rather hard to observe. A tip for turtlers: employ birding tactics. Use your binoculars to scan open muddy banks, logs, and rocks way down the stream. By spotting turtles before you invade their comfort zone, a much closer approach can sometimes be made.

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