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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
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