David T. Kirkpatrick, Ph.D
One of the most distinguished of turtles occurs almost entirely within the borders of the continental United States. Turtles of the genus Graptemys, more commonly known as Map turtles, range through a wide variety of habitats from Florida to Texas, and north to the Dakotas and Quebec. Although they superficially resemble sliders and painted turtles, Map turtles have a number of unique features that set them apart from other semi-aquatic turtles found in the same area. They are a diverse group of turtles, with many beautifully marked species, each type possessing distinctive habits, diets and environmental preferences.
Map turtles follow the general body plan of the more common sliders and painted turtles. However, unlike those turtles, most Map turtles have a well-defined keel running down the middle of the carapace. In a number of species this keel also has rather large knobs or spines jutting upward or backward. This feature is responsible for the Map turtles' other common name: Sawback turtles. The marginal scutes at the rear of the carapace also project backwards in most Map turtles, giving the back of the turtle a decidedly serrated appearance. Some species have a very large head and jaws, designed to allow the turtle to crush mollusks and snails. And finally, of course, the most noticeable difference is the reason that Map turtles are so named - the distinctive thin lines covering the skin and scutes of the turtle, making it appear as if it were a contour or road map. These fine reticulations lend an air of beauty and elegance to the Map turtle that is hard to equal.
Different species of Map turtle are distinguished by the unique patterns of lines on the head and on the scutes. Another distinction is the size and shape of the spines or knobs on the carapacial keel. For example, Graptemys nigrinoda has very characteristic large black knobs projecting straight up from the keel. Graptemys oculifera has a large orange or yellow ring on each scute on its carapace, while Graptemys flavimaculata has a solid yellow or orange blotch on its scutes.
In Graptemys, males and females are relatively easy to tell apart. As with most turtle species the male has a longer and thicker tail than the female, with the vent posterior to the margin of the carapace. Male turtles of some species (G. flavimaculata, G. nigrinoda, G. oculifera, G. ouachitensis, and G. pseudogeographica) possess elongated claws on their forefeet. Final adult size also can be a distinguishing characteristic. For many adults, the smallest female will be as large as or larger than the largest male. Finally, females of some species, most notably G. barbouri, G. pulchra and G. geographica, develop very large, broad heads with heavy jaws.
Currently there are approximately a dozen species of Map turtle recognized, but this number varies depending on the authority being consulted. For example, Lovich and McCoy recently reviewed the Alabama map turtle, G. pulchra, and determined that it was actually composed of three distinct species rather than one, based on patterning in the marginal scutes and seams and on the head. They named the two newly-proposed species Graptemys ernsti and Graptemys gibbonsi in honor of Carl Ernst and J. Whitfield Gibbons. Only time will tell if these new species are accepted or not. Another case in point revolves around three Map turtles: the False Map turtle, the Mississippi Map turtle, and the Ouachita Map turtle. Each turtle has been separated into its own species or combined with one of the others at some time in its history. Most of the difficulty in assigning relationships is due to the variability in head patterning of the three types. However, Richard Vogt recently published a study that demonstrates that alteration in temperatures during incubation of the eggs can produce patterns that resemble those of other species. This pattern alteration does not breed true, however, and so Vogt distinguishes the False Map turtle and the Ouachita Map turtle as separate species, with the Mississippi Map turtle as a subspecies of the False Map turtle. As with the division of the Alabama Map turtle, the reception this work receives by the scientific community will eventually determine if it is accepted or not. It seems quite possible that there are other, still unrecognized, species of Map turtle inhabiting some remote sections of rivers in the central part of the country.
Habitat for Map turtles varies depending on the species. Many seem to prefer rivers to ponds and lakes; in fact some species are restricted to a single river drainage system. Species such as G. geographica, G. ouachitensis and G. pseudogeographica inhabit ponds and river-bottom swamps in addition to slow-moving rivers. In these species, abundant aquatic vegetation seems to be preferred. Other species (G. versa, G. nigrinoda, G. flavimaculata, and G. oculifera) populate moderate to rapidly flowing streams with sandy or clay bottoms, although limestone, mud and gravel bottomed bodies of water also contain Map turtles. No matter what type of habitat, abundant basking areas are essential.
In their natural habitat, most species of Graptemys are omnivorous eaters. However, the percentage of various types of food making up the turtle's diet varies from species to species, and even in some cases from males to females within a species. The species that develop broad jaws feed on mollusks and snails to a large extent, and in females (whose head and jaws are even larger) this dietary preference can be even more pronounced. Other food items taken include insects, crawfish, worms, aquatic vegetation, and sometimes fish and carrion. In captivity they have been known to eat fish, shellfish, chicken, liver, some types of lettuce, and insects, among other things.
Map turtles are perhaps the shyest of our native aquatic turtles. Although they are avid baskers by nature, they are also extremely aware of their surroundings and will quickly enter the water at the slightest hint of danger. This wariness makes them much harder to observe than painted turtles or sliders. They prefer to use as basking platforms fallen trees and logjams, especially those that are surrounded by water. Because of their wary nature, many details of Map turtle behavior in their natural environment have not yet been fully explored.
For those Map turtles in which courtship and breeding behavior have been described, some common behaviors have been noted. Those species in which the males possess elongated claws apparently use them in approximately the same way as male sliders do. First the male swims past the female and turns to face her. He then vibrates his forelimbs and elongated claws against her cheeks. After performing this courtship maneuver for a variable amount of time the male will mount the female. In species in which the males lack long foreclaws, other behaviors have replaced this sequence. For example, it has been reported that in the Alabama Map turtle the male will vibrate his head against the female's nose, alternating sides rapidly.
Female Map turtles routinely lay multiple clutches during the course of a single breeding season. A moderate number of eggs are laid per clutch, ranging from 5 to 16 eggs, depending on the species. These hatch in 60 to 75 days. Females usually choose well-drained areas for egg deposition, such as sandy beaches or open clearings. The temperature at which the eggs incubate can affect the final sex of the turtle in some species of Map turtle. Incubation at 25 degrees C. gives a high percentage of male turtles, while eggs kept at 30 to 35 degrees C. yield females, at least in G. pseudogeographica, G. geographica, and G. ouachitensis.
Map turtles are not as common in captivity as the sliders and painted turtles and when they are kept, it often seems that only a single individual, usually a male, is present (probably due to the smaller size of males). Map turtles can do well in captivity, but care must be taken to provide the proper type of arrangements. In most ways their care is similar to that required for maintaining sliders and painted turtles.
Map turtles seem to be less tolerant of poor water conditions than other aquatic turtles. Water cleanliness and quality must be maintained for the health of the turtles. As Map turtles are more nervous than other turtles, the location of their enclosure should also be chosen with care. Turtles in a "high-traffic" area may become stressed by the constant attention. This can also lead to shell injuries; turtles that are continually diving off their basking area in a panic are more likely to sustain compression injuries to the edges of their shells, leading to infections and possibly death. Map turtles' nervous dispositions should be taken into account, therefore, when initially setting up an enclosure, whether it be inside or outside.
The size and number of animals kept generally determines the nature of the set-up. For large females, or if multiple animals are being kept, perhaps the best type of container is large tubs or pools, as these can be found in many shapes and sizes. Map turtles can be maintained outside in most of the country, provided that adequate precautions are taken to prevent escape and provisions are made for over-wintering animals. If kept outdoors, the large fiberglass troughs or wading pools can be set into the ground with a surrounding fence or wall to prevent turtles from wandering and to protect them from marauders. Outdoor enclosures allow for the closest to "natural" set-ups, and this may help if captive breeding is desired. Indoor set-ups can also be used, but due to the large size of the adults the enclosures must be big enough to provide adequate room.
Captive breeding of Map turtles should be encouraged. With their beauty and limited numbers in the wild, it seems surprising that only a small number of individuals are working with these turtles extensively. As a group, Map turtles pose problems due to their size and nervous disposition, but these challenges should not be sufficient to deter an ardent herpetoculturist. More captive-born animals would hopefully lessen the drain on wild populations that really should not have to suffer even minor losses.
Given their limited range, Map turtle species are in constant danger. Many different factors, both natural and man-made, can affect their chances of long-term survival. Natural disasters can wipe out localized populations much more readily than dispersed groups. Habitat degradation can also have a major effect on these small populations. Agricultural run-off, waste from upriver industrial sites or cities, and large-scale development along the river's edge all have an impact on local Map turtles. Collection of wild animals, especially of some of the more rare species, has also contributed to declines in populations. Unfortunately, it is not enough to simply protect an area where Map turtles occur. Because they inhabit rivers and not ponds or lakes they can be drastically affected by events happening upstream, beyond the boundary of the protected areas. This is not a problem unique to Map turtles however, but it is one that will need to be dealt with successfully if future generations are going to be able to enjoy observing these shy and uniquely beautiful turtles in their natural environment.
This article copyright 1993 by David T. Kirkpatrick.
Originally published in Reptile & Amphibian
Magazine, November/December 1993, pages 6 - 17.
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