Kiley BriggsViews:
My Introduction to Map Turtles
Growing up in the Southern Lake Champlain Valley, I spent my youth roaming freely through the woods and wetlands, igniting my passion for wildlife. I was particularly fond of reptiles and amphibians, perhaps because they were the largest animals I could catch and hold with my bare hands.
By age 10, I thought I knew every frog, salamander, snake, and turtle near my home. Common Snapping Turtles frequented the shallows where I fished, easily recognized by their large size, drab coloration, and rugged appearance. Painted Turtles were much smaller, had smooth black shells, yellow lines on their head, and red lines on their neck and legs. They often basked on rocks or logs near shore and sometimes swam under the culvert where I fished. As far as I knew, those were the only turtles around, until one summer day when I encountered a turtle that truly puzzled me.
After parking my bike under a culvert where I had set a minnow trap, I spotted a small turtle in a shallow pool. Its tan shell, unlike the usual black or gray, stood out. As I approached, I noticed the posterior of its shell was serrated, kind of like a snapper, and it had yellow stripes all over its neck and legs. I thought perhaps it was a hybrid, half Painted Turtle and half snapper. I had to show my mom, so I placed it in my bucket and got back home as fast as I could. While my mom wasn’t much help at identifying the turtle, my Peterson field guide set me straight – it was a Northern Map Turtle (Graptemys geographica).
The intricate pattern of circular lines on the shell of a Northern Map Turtle are the inspiration for the species’ name, but the pattern can be difficult to see on older specimens due to the shell darkening with age.
How to Identify Northern Map Turtles
In addition to their tan or grayish shells and the yellow markings on their skin, Northern Map Turtles have a few other field marks useful for identification. The intricate markings on the top of their shell resemble contour lines on a topographic map, giving the species its name. Those lines can fade with age as the shell darkens, and they are much easier to see when the turtles are wet.
Northern Map Turtles also have a slight keel running down their back, especially younger specimens. Males are quite a bit smaller than females, topping off around 6 inches. Females, however, can have shells over 10 inches long, which is a remarkable difference compared to most other turtles. Across North America, there are 13 other species of map turtle, and other field marks are required to tell them apart. That isn’t an issue in New England or New York, though, as we only have the one species.
Status and Distribution
After my first encounter with a Northern Map Turtle, I soon learned they are quite common across much of Lake Champlain. Many years later, while conducting surveys for Spiny Softshells in a shallow bay, map turtles outnumbered all other turtles by a wide margin. For every softshell or Painted Turtle I spotted I could expect at least 20-30 maps, sometimes many more.
In Vermont, we only know of Northern Map Turtles from Lake Champlain and a couple smaller nearby water bodies. Elsewhere, Northern Map Turtles can be found across much of the Great Lakes and Mississippi River drainages. While they’re primarily found in larger rivers and lakes in the north, they also inhabit smaller rocky streams in southern areas.
What do Northern Map Turtles Eat?
Like most other freshwater turtles, the Northern Map Turtle has a highly varied diet, but they lean more toward the carnivorous end of the spectrum. The wide heads of females, paired with strong, crushing jaws, allow them to feed on snails and small muscles that many other turtles find challenging to eat. Small fish, crustaceans, other invertebrates, aquatic vegetation, and carrion are also readily consumed by Northern Map Turtles.
Threats
Although Common across much of their range, Northern Map Turtles have declined significantly in some areas. Shoreline development greatly limits the availability of nesting habitat, which can hurt their populations in a couple different ways. For example, nesting females might travel farther from shore, putting them at risk of being killed by predators or cars. The resulting hatchlings then have lower chances of surviving their journeys to water. Also, remaining shoreline nesting habitat can attract larger numbers of turtles, which in turn attracts predators that eat eggs and hatchlings.
Water pollution can hurt the species by threatening mussel populations, which map turtles depend on for food. Invasive species threaten map turtles as well. Zebra mussels, introduced from Europe, can crowd out the Northern Map Turtle’s preferred native foods. And, while evidence for this is scant, competition with introduced populations of Pond Sliders could become a problem for map turtles in the future.
Due to shoreline developments, remaining nesting habitat for Northern Map Turtles can attract many turtles, and predators. To protect hatchlings, conservation groups in several places protect nests and rear hatchlings in captivity through the winter, releasing them in the spring at a larger size and giving them a big head start compared to other hatchlings.
What Should You do if You See a Map Turtle?
As with any turtle, if you find a Northern Map Turtle crossing a road, usually the best thing to do is help it across to whichever side it was headed toward. Odds are it is a female searching for a place to lay eggs. If your state has an active reptile and amphibian atlas, you can also take a photo and submit a report. In Vermont, the recent revelation that we may have breeding populations of Northern Map Turtles outside of Lake Champlain came as a surprise. Were it not for a report to the Vermont Herp Atlas, we might still not know about those turtles.
Much to my regret, a couple years have passed since my last encounter with a Northern Map Turtle. I simply don’t have many opportunities to spend time on Lake Champlain these days, or elsewhere within the species’ range. When I do see map turtles, however, they always brighten my day. But then again, what turtle doesn’t?
