Tortuga Gazette 28(2): 1-3, February 1992

The Bog Turtle, Clemmys muhlenbergii

by Dorothy DeLisle

With an average adult size of 3 to 3.5 inches (7.6 to 8.9 cm) and a record length of 4.5 inches (11.4 cm), the bog turtle or Muhlenberg's turtle (Clemmys muhlenbergii) is generally considered to be the smallest turtle native to the United States, although the flattened musk turtle (Sternotherus depressa) runs a close second. Bog turtles hatch with a carapace length of about 1 inch (2.5 cm), making them enormous hatchlings relative to their adult size.

The carapace of Muhlenberg's turtle is light brown to mahogany to black with a lighter center or, often, a yellowish or reddish sunburst pattern on each scute. A low dorsal keel is present. Carapacial growth annuli may or may not be present, but are never as raised as those of its close relative the wood turtle (Clemmys insculpta). Bog turtles are flat at hatching, and become more domed with age. The plastron is brown to black with small areas of a lighter hue.

The bog turtle's trademark is a large patch of orange, red or yellow on the temporal region of the head often extending onto the neck, as shown in the photograph. Occasionally, the patch is split into two parts. The dark limbs are usually suffused with red, orange, or yellow mottlings.

Male bog turtles have a larger head, a longer, thicker tail with a more posterior vent, longer front claws, and a wider and less high shell than females. Additionally, males have a concave plastron, whereas females have a flat plastron with a wide notch at its posterior margin. Sexual maturity is thought to be at 7.0 to 7.5 cm (about 3 inches), which in the wild occurs at 5 to 8 years.

Mating occurs from April to June. The male grasps the female's shell with all four of his feet and bangs his shell against hers in typical Clemmys fashion. Nesting occurs from late May to July. From one to six (typically two to four) eggs are laid at the base of tussocks or on top of sphagnum in a 2 inch deep cavity which is covered with vegetation. Occasionally, females may lay multiple clutches. The eggs hatch in 49-60 days. The young emerge in August to September or may over-winter in the nest and emerge in the spring.

The bog turtle has a very spotty distribution and is broken down into two "mega" populations: northern and southern. The many northern populations are unevenly scattered through New York, Massachusetts, Connecticut, Pennsylvania, New Jersey, Delaware, Maryland and, possibly, Rhode Island. The northern populations occur at low elevation (0 to 1000 feet) and relatively close to either the ocean or the Great Lakes. The few southern populations are found in select areas of Virginia, North and South Carolina, Georgia, and Tennessee. They are found at higher elevations (2000 to 4000 feet) and are far removed from the influence of any large body of water.

Muhlenberg's turtles are habitat specialists being found in bogs, swamps, and wet meadows. They require full sunlight, an abundance of grassy or mossy cover, and spring seepage. They prefer mucky-bottomed waters into which they can dive and quickly bury themselves.

Bogs, swamps and wet meadows are successional habitats, that is, habitats which by nature have short lifetimes. It is only a matter of time before most bogs will become overgrown with trees and shrubs or fill in and dry up. In the past, natural phenomena such as wild-fires and animals such as beavers helped to maintain or create new bogs. With man's interference in these processes (not to mention his direct draining and destruction of bogs), bogs are disappearing at a rate greatly exceeding the rate at which they are being formed. Additionally, roads and other obstacles, combined with the destruction of surrounding areas, isolate bogs and make it difficult for bog turtle populations to relocate naturally.

Because bog turtles are extremely secretive, they are difficult to find. Indeed, they were not confirmed to occur in several of the above states until the 1980's. On one level, they are more secretive than rare. On the other level, many entire populations are disappearing or have disappeared. In a recent survey by the state of New York on its 76 historically known bog turtle populations, 47% of the sites were now unsuitable habitat with 26% having been physically destroyed by man and 21% having been lost to the natural process of habitat succession. Only 14% of the remaining sites were judged to be of excellent quality, and the remaining 39% were in fair to good condition depending on the degree of succession.

Although habitat destruction is the major threat to bog turtle populations, pesticides, fertilizer run-off, water pollution and collection also have significant impacts. Invasion of exotic plants, such as purple loosestrife (Lythrum salicaria) and giant reed (Phagmites australis), into bog turtle habitats in some areas has impacted on the turtles by the non-native plants forming dense patches of vegetation which impede movement and produce shade.

Many populations of bog turtles now have less than 20 individuals, and some have under 10. It is easy to see how precarious these populations are, and how collection or loss of just one individual can have an impact on the survival of the population. Current management strategies include prevention of the filling or draining of bogs, prohibition of collection, and controlled burns and tree removal to prevent loss of bog habitat by succession.

Bog turtles are omnivorous and will eat in or out of the water. In captivity, they will take prepared foods as well as more natural fare. They should be kept in a simulated bog setup, details of which can be found in the references listed below. Bog plants for your enclosure can be collected from areas where it is legal to do so, or can be purchased from mail order specialty nurseries. Specialty nurseries selling suitable plants can be found in the advertising section of almost any gardening magazine.

References

Collins, D. (1991) Western New York bog turtles (Clemmys muhlenbergii): Perspectives on captive propagation. In R. L. Gowen (ed.), Captive Propagation and Husbandry of Reptiles and Amphibians, 1989. Northern California Herpetological Society Special Publication #5, pp. 17-23.
DeGraaf, R. M. & D. D. Rudis (1983) Amphibians and Reptiles of New England - Habits and Natural History. Univ. Mass. Press, Amherst.
Ernst, C. H. & R. W. Barbour (1972) Turtles of the United States. University of Kentucky Press, Lexington, pp. 76-79.
Herman, D. W. (1989) Captive management of eastern Clemmys at Zoo Atlanta with emphasis on Clemmys muhlenbergii. In M. Rosenberg (ed.), 12th International Herpetological Symposium on Captive Propagation and Husbandry, New York/New Jersey Metropolitan Area, June 15-18, 1988, pp. 39-45.
Herman D. W. (1991) Captive husbandry of the eastern Clemmys group at Zoo Atlanta. In K. Beaman, F. Caporaso, S. McKeown & M. Graff (eds.), Proceedings First International Symposium on Turtles & Tortoises: Conservation and Captive Husbandry, Orange, CA, August 9-12, 1990, pp. 54-62.
Herman, D. W. & G. A. George (1986) Research, husbandry and propagation of the bog turtle Clemmys muhlenbergi at the Atlanta Zoo. In F. Caporaso & S. McKeown (eds.), 9th Int. Herpetological Symposium on Captive Propagation and Husbandry, San Diego, CA, June 26-30, 1985, pp. 125-136.
Tyron, B. W. & D. W. Herman (1991) Status, conservation and management of the bog turtle, Clemmys muhlenbergii, in the Southeastern United States. In K. Beaman, F. Caporaso, S. McKeown & M. Graff (eds.), Proceedings First International Symposium on Turtles & Tortoises: Conservation and Captive Husbandry, Orange, CA, August 9-12, 1990, pp. 36-53.