Article and photos by Linda Hagan, Maryland Master Naturalist Intern
The Northern Map Turtle is an aquatic, fresh water turtle that inhabits large rivers, streams and lakes. They spend much of their time underwater although they do require abundant basking sites, but they are shy and will dive for safety at any disturbance. Map turtles usually forage for food in the morning and late afternoon and prefer to bask at midday.
Northern Map turtles get their name from their appearance. The carapace (top shell) has a shallow but definite midline keel. It is olive colored and has designs that resemble a map, some say the lines look like waterways or topographic lines on a map. The lines are yellow to orange in color with darker colors in between them in greens and browns. Any pattern may be obscured by dark pigmentation in females or algae growth on the carapace. The skin is olive to brown black with thicker yellow to greenish yellow stripes on the skin of their face and limbs. The skin design can be more noticeable due to the fact the shell can fade with age. The plastron (bottom shell) is pale yellow in adults but juveniles have a black pigment along the scute (plate) line. The Northern Map Turtles also have a large jaw surface which give the appearance of light colored lips.
Map turtles assemble in groups to hibernate and spend their winters in deep, riverine pools where the water is cold and has a high level of oxygen. There they will lie motionless on the bottom fully exposed. They are able to breathe underwater because they take up oxygen through permeable skin that is well supplied with blood.
Male Map Turtles have narrower heads, oval-shaped carapace and longer, thicker tails than the females do. The females are larger than the males with a carapace measuring up to 10.5” compared to the males with a 6.2” carapace.
Breeding takes place in both spring and fall. Nests are usually built on open, sandy beaches or sand bars rather than wooded areas. The egg laying process can take many hours, beginning at nightfall and lasting until early morning. The female will lay 10-13 eggs per clutch and usually lays two clutches a year. Map turtles have temperature dependent sex determination. Warmer temperatures produce females and cooler temperatures males. Males reach sexual maturity at around 4-6 yrs of age but females can take more than 10 yrs to mature. The predators of their nest sites are raccoons, skunks, foxes, and river otters. Gulls, crows, grackles and red-winged blackbirds will eat hatchlings. Adult turtles can also be prey to skunks, raccoons, coyotes and opossum.
Map Turtles feed on a variety of food sources. Algae, vascular plants, dead fish, snails, clams, crayfish and a wide variety of insects.
Where many turtles such as the Eastern Box Turtle can live 75 yrs or more, the Map Turtle usually lives from 20-25 years of age. There are 13 species of Map Turtles. The Map Turtle we have living at FountainRock is a Mississippi Map Turtle named “Kohni” who came to live with us in 2014 on a rainy spring day. When counting Kohni’s scutes at the time of her arrival it was estimated she was around 15 years of age. Come visit beautiful Kohni and see why she is called a Map Turtle.
The Northern Map Turtle has been listed as endangered in Maryland because of its restricted range. Threats such as water pollution, waterfront development, vehicle traffic, boat propellers, habitat destruction, siltation, dams, and collection for the pet trade are all causes of the endangered status the Northern Map Turtle faces. It is up to humans in the private and public sectors to join together to protect and restore habitat if we want to see these beautiful turtles continue to be part of our diverse ecosystems.