Description and Identification

Graptemys geographica is a medium to large map turtle. Females will typically reach 8-10”(20.3-25.4cm), max 10.7” (27.3cm), while males stay smaller at 4-5.5” (10.2-14cm), max 6.3” (16cm). The carapace is olive green to brown with a fine, yellow, reticulating pattern which has been known to fade slightly with age. The carapace has a defined, but low keel and its posterior edge is serrated. Small vertebral spines are noticeable in hatchlings and juveniles, but disappear completely in adult females. The plastron is cream to yellow with a seam following pattern that vanishes with age. The skin of the head, neck, legs, and tail is olive to dark olive with yellow markings. The post-orbital mark is round or triangular and does not connect to the head stripes. The chin and throat are marked with a number of longitudinal stripes, the widest being the middle stripe. Female G. geographica have heads that get considerably large as they age. The head of the male stays more proportional to the size of the turtle. The eyes are yellow in color with a transverse bar through the pupil. The beak will also be yellow. Males will have longer and wider tails with the cloacal opening 1/2 to 2/3rds of the way down the tail and a more juvenile appearance. Females will have shorter, narrower tails, a much larger build, and as mentioned before, much broader heads.

Distribution

The Northern Map Turtle has the largest distribution of any turtle in the genus and is the only member of the genus inhabiting watersheds that drain into the Atlantic Ocean. Populations exist from southern Quebec and northwestern Vermont along the St. Lawrence drainage system west through the Great Lakes: Michigan, Wisconsin, and southern Minnesota. The western edge of the range continues south through eastern Iowa, much of Missouri, far eastern Kansas, the corner of Oklahoma, and a large portion of Arkansas, possibly into the northern reaches of Louisiana. The species is widespread through Illinois, Indiana, Ohio, south into Kentucky, Tennessee, northern Alabama and parts of Georgia and Mississippi. Western sections of West Virginia, Virginia and North Carolina are also home to G. geographica. Smaller populations exist in Maryland, Pennsylvania, and New Jersey. The populations of these three states are restricted mainly to portions of the Susquehanna, Juniata, Delaware, and possibly Allegheny rivers. An isolated population has been observed in the Hudson River of Eastern New York State.

Native Habitat

G. geographica most frequently inhabits large bodies of water, such as rivers and lakes, but there are exceptions to this rule. In the northern part of their range, they seem to have a slight preference toward deep, slowly moving areas; in the eastern, southeastern, and far western parts of their distribution, they prefer rapidly flowing habitats with stony or gravelly bottoms. Locations with a profusion of basking locations are ideal.

Wild Diet

Mollusks and gastropods are main sources of food for adults, both male and female, though males seemingly add more insects to their diet than females. Crayfish is another popular prey item for the Northern Map Turtle. Juveniles of both sexes also have a fondness for mussles and snails. The primary vegetation included in their diet is filamentous algae.

Behavior

Graptemys geographica is mainly diurnal, foraging in the morning and late afternoon and basking inbetween. With such a large distribution, length of the active season is based on location. Those in the northern part of the range are typically active from April through late October, while those in the southern part of the range will have a longer active season. Overwintering sites also vary from habitat to habitat; those in Pennsylvania are fond of deep riverine pools, while in Kentucky, they tend to use impoundments. In a Vermont study by Graham and Graham in 1992, the majority of hibernating turtles were congregated together, fully exposed at the bottom of a 6.7m depression in the river. Here in Vermont, this species has been observed moving about on the river bottom with water temperatures as low as 33-43F (0.5-6C) and ice covering the top of the river.

Reproduction

There is little information available on the maturation of this species. A study from the early 1900s reports that the smallest nesting female found was 7.5” (19cm) SCL. Courtship and mating occur in both spring and fall. A common courtship ritual is for the male to position himself in front of the female, making nose-to-nose contact, then bobbing his head up and down with great frequency. This act is followed by the male swimming behind the female and attempting to make cloacal contact. Once this occurs, he will attempt to mount the female by hooking his tail around hers.