Common map turtle
The northern map turtle (Graptemys geographica ), also known as the common map turtle, is an aquatic turtle in the family Emydidae. It is endemic to North America.
The Northern map turtle is an aquatic turtle native to North America. It gets both its common and scientific names from the markings on its carapace, which resemble contour lines on a map or chart. These lines are usually shades of yellow, tan, or orange, and are surrounded by dark borders, with the rest of the carapace being olive or greyish brown. However, the carapace markings tend to fade as the animal matures, and in older individuals are usually only visible when the shell is wet. The plastron is yellowish and is marked by a central dark blotch (plastral figure) that follows the sutures of the plastral scutes and fades with age so that many adults lack a pattern all together. The head, neck, limbs, and tail are dark green with thin yellow stripes, and an oval or triangular spot is located behind each eye. Females have a much wider head than males and this is associated with differences in feeding. Males have a narrower carapace with a more distinct keel, narrower head, and a longer, thicker tail.
Northern map turtles occur from southern Quebec and Ontario to northern Vermont where they live in the St. Lawrence River drainage basin. Their range extends west through the Great Lakes and into southern Wisconsin and eastern Minnesota, west of the Appalachians, south to Kansas and northwestern Georgia. They also occur in the Susquehanna River system in Pennsylvania and Maryland and the Delaware River. These turtles inhabit ponds, rivers, and lakes. They prefer large bodies of water and areas with fallen trees and other debris for basking.
Northern map turtles are social in their lifestyle. They typically bask in groups and are diurnal, meaning they are active exclusively in daylight hours. These turtles are also quite shy and difficult to approach; they usually slip into the water and hide at the first hint of danger. Like most other aquatic turtles, they always feed in the water. Northern map turtles are dormant (hibernation-like state) around November through early April depending on local climatic factors. They spend the winter underwater and do not surface to breathe, especially when ice cover makes this impossible. Adults rest on the bottom or wedged underneath rocks or logs and often hibernate communally with other Northern map turtles where they may remain somewhat active. Hibernacula must be well oxygenated because map turtles need to absorb oxygen from the water to survive the winter.
Norhtern map turtles are carnivores. Adult females have wide heads, strong jaws and broad alveolar crushing surfaces in their mouths which they use to feed on mollusks, their primary prey, as well as insects and crayfish. Adult males are much smaller and have narrower heads and feed on smaller mollusks and insects.
Northern map turtles breed in the spring and fall. The nesting period lasts from May to July. The female usually chooses unshaded well-drained areas for depositing the eggs. The nest cavity is dug with the hind feet. The size of the clutch is between 6 and 20 eggs which are oval, about 3.2 cm (1.3 in) long, and have a flexible shell. After the eggs are laid, the cavity is filled. The incubation period lasts 50 to 70 days, and most hatchlings emerge from August to September. When a nest hatches late, the hatchlings may overwinter in the nest. The female usually lays 2 or more clutches in one breeding season. The gender of the young is determined by the temperature. At 25 °C (77 °F), incubation produces a majority of males, whereas 30 to 35 °C (86 to 95 °F) yields more females. Male Northern map turtles become reproductively mature at the age of 4 years while females mature when they are 10-12 years old.
The main threats to Northern map turtles include degradation and destruction of their habitat, pollution, collisions with vehicles especially during the nesting period, bycatch, and collection for food and for the pet trade. Climate change may pose a future threat to this species.
According to IUCN, the Northern map turtle is locally common throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List, and its numbers today are stable.
