Northern Map Turtle
Encyclopedia
The northern map turtle (Graptemys geographica), or formerly common map turtle, is an aquatic turtle
that belongs to the family Emydidae
.
. The light markings resemble contour lines on a map or chart. The lines on the carapace are shades of yellow, tan, or orange and are surrounded by dark borders. The rest of the carapace is olive or greyish brown. The carapace
markings on older individuals tend to fade but are usually still apparent when the shell is wet. The carapace has a hydrodynamic appearance and is broad with a moderately low keel. The rear of the carapace is flared and the rear marginals form serrations. 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 (i.e., the plastron is immaculate). The head, neck and limbs are dark olive, brown, or black with thin yellow or green stripes. There is an oval or triangular spot located behind the eye. Like other map turtles, this species exhibits extreme sexual size dimorphism
. Males are 10–16 cm (3.9–6.3 in) in carapace length and weigh between 150–400 g (5.3–14.1 oz), while females are 18–27 cm (7.1–10.6 in) in carapace length and weigh around 0.5 kilogram. Females have a much wider head than males and this is associated with differences in feeding. Males have a narrower carapace with more distinct keel, narrower head, and a longer, thicker tail. Unlike females, the opening of the cloaca is beyond the rear edge of the carapace. Young map turtles have a pronounced dorsal keel. Hatchlings have a round grayish-brown carapace that is about 2.5 cm (0.984251968503937 in) long.
and into southern Wisconsin and eastern Minnesota, west of the Appalachians, south to Kansas, northwestern Georgia. It also occurs in the Susquehanna River
system located in Pennsylvania and Maryland and also in the Delaware River
.
for basking. These turtles are more often found in rivers than in lakes or ponds. They are found in larger rivers and lakes in the northern portion of their range but are more likely to live in smaller rocky rivers and streams in the south and west.
must be well oxygenated because, unlike some other turtle species such as painted turtle
s, map turtles need to absorb oxygen from the water in order to survive the winter. They are avid baskers and they bask in groups. They are diurnal. They are also a very wary animal; at the slightest hint of danger they slip into the water and hide.
in the spring and fall. Most mating takes place in deep waters. The nesting period lasts from May to July. Unshaded sites with sandy soil is highly preferred. The female usually chooses well-drained areas for depositing the eggs. The nest cavity is dug with the hind feet. The size of the clutch is between 6 to 20. The eggs
are oval and have a flexible shell that is about 3.2 cm. After the eggs are laid the cavity is filled. They hatch between 50 to 70 days of incubation and most emerge in August to September. When a nest hatches late, the northern map turtle has been known to overwinter in the nest. The female usually lays two or more clutches in one breeding season. The sexes of the young are determined by the temperature. At 25 degrees Celsius incubation produces a majority of males whereas 30–35 °C (86–95 F) yields more females.
, and the northern map turtle is no exception. Adult females have wide heads and broad alveolar crushing surfaces in their mouths which they use to feed on molluscs, their primary prey, as well as insects and crayfish
. Adult males are much smaller and have narrower heads and feed on smaller molluscs and insects. Like most other aquatic turtles, feeding always takes place in the water. In places where invasive
molluscs such as Zebra mussels and Asian clams (Corbicula fluminea
) are abundant they may become the most important food of female northern map turtles.
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
that belongs to the family Emydidae
Emydidae
Emydidae, commonly called the pond turtles or marsh turtles, is a family of turtles. Previously, several species of Asian box turtle were classified in the family. However, revised taxonomy has separated them to a different family. Now, Emydidae, with the exception of two species of pond turtle,...
.
Description
The northern map turtle gets both its common and scientific names from the marking on the skin and carapaceCarapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
. The light markings resemble contour lines on a map or chart. The lines on the carapace are shades of yellow, tan, or orange and are surrounded by dark borders. The rest of the carapace is olive or greyish brown. The carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
markings on older individuals tend to fade but are usually still apparent when the shell is wet. The carapace has a hydrodynamic appearance and is broad with a moderately low keel. The rear of the carapace is flared and the rear marginals form serrations. 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 (i.e., the plastron is immaculate). The head, neck and limbs are dark olive, brown, or black with thin yellow or green stripes. There is an oval or triangular spot located behind the eye. Like other map turtles, this species exhibits extreme sexual size dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. Males are 10–16 cm (3.9–6.3 in) in carapace length and weigh between 150–400 g (5.3–14.1 oz), while females are 18–27 cm (7.1–10.6 in) in carapace length and weigh around 0.5 kilogram. Females have a much wider head than males and this is associated with differences in feeding. Males have a narrower carapace with more distinct keel, narrower head, and a longer, thicker tail. Unlike females, the opening of the cloaca is beyond the rear edge of the carapace. Young map turtles have a pronounced dorsal keel. Hatchlings have a round grayish-brown carapace that is about 2.5 cm (0.984251968503937 in) long.
Variation
In early summer in southeast Michigan (according to a study done by R. Irwin) The Northern Map Turtle will display a reddish color in the most front part of their carapace. This was only seen in turtles ranging from 6–10 cm (2.4–3.9 in). The reason for this coloration is still unknown.Distribution
Northern map turtles inhabit an area from south Quebec and Ontario to northern Vermont where it lives in the St. Lawrence River drainage basin. Its range extends west through the Great LakesGreat Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
and into southern Wisconsin and eastern Minnesota, west of the Appalachians, south to Kansas, northwestern Georgia. It also occurs in the Susquehanna River
Susquehanna River
The Susquehanna River is a river located in the northeastern United States. At long, it is the longest river on the American east coast that drains into the Atlantic Ocean, and with its watershed it is the 16th largest river in the United States, and the longest river in the continental United...
system located in Pennsylvania and Maryland and also in the Delaware River
Delaware River
The Delaware River is a major river on the Atlantic coast of the United States.A Dutch expedition led by Henry Hudson in 1609 first mapped the river. The river was christened the South River in the New Netherland colony that followed, in contrast to the North River, as the Hudson River was then...
.
Habitat
The northern map turtle inhabits ponds, rivers and lakes. They prefer large bodies of water and areas with fallen trees and other debrisDebris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
for basking. These turtles are more often found in rivers than in lakes or ponds. They are found in larger rivers and lakes in the northern portion of their range but are more likely to live in smaller rocky rivers and streams in the south and west.
Ecology and behaviour
This turtle is dormant from approximately November through early April depending on local climactic factors. Northern map turtles spend the winter under water 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. HibernaculaHibernaculum (zoology)
Hibernaculum plural form: hibernacula is a word used in zoology to refer to a place of abode in which a creature seeks refuge, such as a bear using a cave to overwinter. Insects may hibernate to survive the winter. The word can be used to describe a variety of shelters used by various kinds of...
must be well oxygenated because, unlike some other turtle species such as painted turtle
Painted Turtle
The painted turtle is the most widespread native turtle of North America. It lives in slow-moving fresh waters, from southern Canada to Louisiana and northern Mexico, and from the Atlantic to the Pacific. The turtle is the only species of the genus Chrysemys, which is part of the pond turtle...
s, map turtles need to absorb oxygen from the water in order to survive the winter. They are avid baskers and they bask in groups. They are diurnal. They are also a very wary animal; at the slightest hint of danger they slip into the water and hide.
Reproduction
Northern map turtles breedBreed
A breed is a group of domestic animals or plants with a homogeneous appearance, behavior, and other characteristics that distinguish it from other animals or plants of the same species. Despite the centrality of the idea of "breeds" to animal husbandry, there is no scientifically accepted...
in the spring and fall. Most mating takes place in deep waters. The nesting period lasts from May to July. Unshaded sites with sandy soil is highly preferred. The female usually chooses well-drained areas for depositing the eggs. The nest cavity is dug with the hind feet. The size of the clutch is between 6 to 20. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are oval and have a flexible shell that is about 3.2 cm. After the eggs are laid the cavity is filled. They hatch between 50 to 70 days of incubation and most emerge in August to September. When a nest hatches late, the northern map turtle has been known to overwinter in the nest. The female usually lays two or more clutches in one breeding season. The sexes of the young are determined by the temperature. At 25 degrees Celsius incubation produces a majority of males whereas 30–35 °C (86–95 F) yields more females.
Diet
Map turtles are more carnivorous than most other members of the family EmydidaeEmydidae
Emydidae, commonly called the pond turtles or marsh turtles, is a family of turtles. Previously, several species of Asian box turtle were classified in the family. However, revised taxonomy has separated them to a different family. Now, Emydidae, with the exception of two species of pond turtle,...
, and the northern map turtle is no exception. Adult females have wide heads and broad alveolar crushing surfaces in their mouths which they use to feed on molluscs, their primary prey, as well as insects and crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
. Adult males are much smaller and have narrower heads and feed on smaller molluscs and insects. Like most other aquatic turtles, feeding always takes place in the water. In places where invasive
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
molluscs such as Zebra mussels and Asian clams (Corbicula fluminea
Corbicula fluminea
Corbicula fluminea is a species of freshwater clam, an aquatic bivalve mollusk in the family Corbiculidae.This species is of originally mainly Asian origin and thus it is often commonly called Asian clam or Asiatic clam. In the aquarium and koi pond trade it is often called Golden Clam or Golden...
) are abundant they may become the most important food of female northern map turtles.