Common Map Turtle (Graptemys geographica)

Photos by J.D. Willson unless otherwise noted

Description: Northern map turtles, also called common map turtles, are the most abundant and widespread of all map turtle species. The carapace length of females can be as great as 27 cm (10.5 in). Males, on the other hand, are usually less than 16 cm (6.2 in) long. While females have an enlarged jaw and grow to a greater size, this difference is not as extreme as it is in other map turtle species. The carapace is olive green and has an intricate system of faint yellow lines that resemble a topographical map. Any patterning may be obscured by dark pigmentation in females or by algae. Northern map turtle skin is olive to dark brown and contains yellow or greenish markings. The carapace has a shallow but definite midline keel, though the keel lacks distinctive spines or knobs. These turtles consistently have a small postorbital blotch that resembles a triangle with rounded points. They also maintain a j-shaped yellow line on the lower side of the neck that arches upward as it nears the head.

Distribution and Habitat: The northern map turtle is a widespread species and occurs as far north as Quebec and as far south as Alabama and Arkansas. They inhabit northeastern drainages that empty into the Atlantic Ocean. Also found in several southeastern drainages that empty into the Gulf of Mexico, they are not present in much of the Mississippi River or adjacent waterways. Individuals of this species prefer large bodies of water, mainly rivers, large streams, and lakes rather than creeks and ponds. They require abundant basking sites, although they are wary baskers. Northern map turtles are most likely to be found in clear, flowing aquatic habitats with gravel substrates.

Reproduction and Development: Breeding occurs in both the spring and fall, and most nesting probably takes place from late May to mid-July. The eggs hatch in late summer, but hatchlings will often delay emergence until the end of winter. Nests are typically built on open, sandy beaches or sandbars rather than wooded areas. They are never far from the water. The process of laying eggs may take many hours, often beginning at nightfall and lasting until early in the morning. Clutch size averages 10-12 eggs with females producing 2 or 3 clutches a year. Incubation, which takes about 75 days, determines sex as with many turtle species. Warmer temperatures produce females while cooler temperatures produce males. Males probably reach sexual maturity after 4-6 years, while females may take more than 10 years to mature.

Habits: Hatchlings quickly move downstream in order to scout out a summer home range. Adults are mostly active during the day, feeding on snails and other mollusks, crayfish, freshwater mussels, and aquatic insects in the morning and late afternoon. Their diet does not include a large amount of vegetation; what they do consume is ingested incidentally. When not feeding, they can be found basking. Northern map turtles exhibit annual movement patterns in both the late spring and summer. These patterns are mostly seen in males who move to various locations away from their overwintering grounds. During the winter, map turtles tend to hibernate in deep, slow, riverine pools and impoundments. They remain exposed rather than burying themselves in mud. Common predators of nests include raccoons, skunks, foxes, and river otters, while gulls, crows, grackles, and red-winged blackbirds will eat hatchlings. Raccoons will also predate upon adults, as will opossums, skunks, and coyotes.

Conservation: Northern map turtles are listed by the IUCN as a species of least concern. Their population size has likely declined where water quality, and thus freshwater mollusk populations, has decreased. However, the introduction of invasive zebra mussels has probably aided the species, and, at present, it seems stable.

Pertinent References:
Buhlmann, Kurt, Tracey Tuberville, and Whit Gibbons. Turtles of the Southeast. Athens: University of Georgia, 2008.

Conant, Roger, and Joseph T. Collins. A Field Guide to Reptiles & Amphibians: Eastern and Central North America. 3rd ed. Boston: Houghton Mifflin, 1998.

Jensen, John B., Carlos D. Camp, Whit Gibbons, and Matt J. Elliott. Amphibians and Reptiles of Georgia. Athens: University of Georgia, 2008.

Account Author: Lindsay Partymiller