Bog Turtle

Clemmys muhlenbergii

Description

The bog turtle is the smallest member of the genus Clemmys, with the carapace (upper shell) of adults measuring 3-4.5 in (7-11 cm) in length. The domed carapace is weakly keeled and ranges in color from light brown to ebony. The scutes of the shell often have lighter-colored centers resembling a starburst pattern. The plastron (lower shell) is brownish-black with contrasting yellow or cream areas, often along the midline. This species is readily distinguished from other turtles by the large, conspicuous bright orange, yellow, or red blotch found on each side of the head. The species is sexually dimorphic. Males have concave plastrons and long, thick tails, and the vent of the male is located beyond the posterior carapace margin. Females have proportionately higher carapaces, flat plastrons, and relatively short tails, and the vent of the female is located beneath the carapace edge.

Behavior

Bog turtles are semi-aquatic and are only active during part of the year. In the northern part of their range, they are active from April to mid-October. Reported periods of inactivity in July and August may be an artifact of collecting bias and the difficulty of locating turtles at that time of year. Bog turtles hibernate from October to April, often just below the upper surface of frozen mud or ice. Their varied diet consists of beetles, lepidopteran larvae, caddisfly larvae, snails, nematodes, millipedes, fleshy pondweed seeds, sedge seeds, and carrion.

Female bog turtles reach sexual maturity between five and eight years of age. Mating occurs in May and June, and females deposit from two to six white eggs in sphagnum moss or sedge tussocks in May, June, or July. Unlike most other semi-aquatic turtles, bog turtles do not leave their wetland habitat and travel to dry, upland areas to lay eggs. Instead, they select slightly elevated sites, generally on Carex stricta tussocks, for nesting within their marshy habitat. Nesting areas typically have limited canopy closure, support an array of moisture tolerant, low vegetation, and provide ample solar exposure. The eggs hatch after an incubation period of 42-56 days, and the young emerge in August or early September. Infertile eggs are common, and not all females produce clutches annually. Also, there is no evidence to suggest that multiple clutches are deposited in a single season.

Habitat

Bog turtles inhabit shallow, spring-fed fens, sphagnum bogs, swamps, marshy meadows, and pastures which have soft, muddy bottoms; clear, cool, slow-flowing water, often forming a network of rivulets; and open canopies. In Maryland, bog turtles were found in circular basins with spring-fed pockets of shallow water, a substrate of soft mud and rock, dominant vegetation of low grasses and sedges, and interspersed wet and dry pockets. In these types of habitats, bog turtles often utilize the runways of muskrats and meadow voles. Bog turtles have been found at elevations ranging from near sea level in the north to 4,500 ft (1,371 m) in the south. Bog turtles usually occur in small, discrete populations occupying suitable wetland habitat dispersed along a watershed. These wetlands are a mosaic of micro-habitats which include dry pockets, saturated areas, and areas that are periodically flooded. They depend upon this diverse hydrological mosaic, utilizing shallow water in spring, and returning to deeper water in winter. Unless disrupted by fire, beaver activity, grazing, or periodic wet years, open-canopy wetlands are slowly invaded by woody vegetation. They undergo a transition into closed-canopy, wooded swamplands that are unsuitable for habitation by bog turtles.

Historically, bog turtles probably moved from one open-canopy wetland patch to another, as succession closed wetland canopies in some areas, and natural processes opened canopies in other areas.

Several plant species commonly associated with bog turtle habitats include alders, willows, sedges, sphagnum moss, jewelweed, rice cut-grass, tearthumb, arrow arum, red maple, skunk cabbage, and bulrushes. Pedestal vegetation, such as tussock sedge and sphagnum moss, are utilized for nesting and basking.

Currently, many wetlands occupied by bog turtles in agricultural areas are subject to livestock grazing. Light to moderate grazing may function to impede succession by preventing or minimizing the encroachment of invasive native and exotic plant species, thereby maintaining an intermediate stage of succession. It has been suggested that in pre-colonial times the grazing activities of large herbivores, such as bison and elk, may have been important in maintaining bog turtle habitat. The occurrence of bog turtles in wetlands grazed by livestock is probably an instance where grazing by livestock has either replaced grazing by native herbivores or replaced one of the other historical factors that would have acted to maintain the wetlands in an early successional stage.

Distribution

Due to the bog turtle's rarity, small size, predator-evasive behavior (i.e., tendency to burrow rapidly into the mud), and habitat preferences (e.g., dense herbaceous vegetation), it is difficult to obtain reliable bog turtle population demographics. This lack of data has led to a misconception as to the number of healthy populations found throughout the species' range. For example, some documented bog turtle sites support populations consisting primarily of old individuals. These populations are slowly disappearing due to negligible recruitment of juveniles over a sustained period of time.

The bog turtle is sparsely distributed over a discontinuous geographic range extending from New England south to northern Georgia. A 250-mi (402-km) gap within the range separates the species into distinct northern and southern populations. The northern population extends from southern New York and western Massachusetts southward through western Connecticut, New Jersey and eastern Pennsylvania, to northern Delaware and Maryland. Disjunct populations previously occurred in western Pennsylvania and in the Lake George and Finger Lakes regions of New York. The western Pennsylvania and Lake George populations have been extirpated, and only a remnant population exists at one remaining site in the Finger Lakes region. The southern population occurs in the Appalachian Mountains from southwestern Virginia southward through western North Carolina, eastern Tennessee, northwestern South Carolina, and northern Georgia. The southern population also occurs in the upper piedmont of North Carolina. Researchers question the taxonomic status of the northern and southern populations. Initial data from recent preliminary genetic studies, based on examination of variability at the 16S ribosomal gene, suggest that there may not be significant genetic differences between the northern and southern populations. However, due to the conservative nature of this gene in other species, any definitive conclusions concerning genetic differences between the northern and southern populations is premature.

Threats

Based on documented losses of bog turtles and their habitat, the northern population has declined by at least 50%, with most of the decline occurring over the last 20 years. Habitat destruction and illegal collecting for the pet trade are the primary threats to the species. Widespread alteration of bog turtle habitat has resulted from the draining, ditching, dredging, filling, and flooding of wetlands for residential, urban, and commercial development; road construction; agricultural activities; and pond and reservoir construction. The proximity of many remaining bog turtle populations to rapidly developing areas also poses a significant threat to the species.

Although historically, bog turtles probably moved from less suitable wetlands (e.g., those undergoing succession) to more suitable wetlands (e.g., those recently formed, or where succession was set back by natural processes), it is much less likely that such movements would be successful today. Bog turtle habitats are now highly fragmented, making successful immigration difficult due to loss of wetland travel corridors, and the prevalence of roads, subdivisions, and agricultural land near or encircling many sites. In addition, more habitat is becoming unsuitable, and fewer potentially suitable wetland sites are becoming available because those natural processes that served to maintain and create bog turtle habitat have been suppressed or are no longer operative.

Habitat loss is a major factor for the past and present decline of bog turtles throughout much of their range. Wetland habitats have been drained and filled for development, agriculture, road construction, and impoundments. These activities have also severely fragmented the remaining habitat and have created physical barriers to movement, thus isolating existing bog turtle populations from other such sites.

Even when located in upland areas, development and agriculture can also cause indirect hydrological alterations of adjacent wetland habitats. If these alterations present a barrier to surface water or groundwater flow, the wetland can become wetter or drier, either of which may render the habitat less suitable or unsuitable for bog turtles. If surface water flow is intercepted, groundwater recharge may be reduced, potentially reducing water levels in adjacent wetlands.

The concentration of storm water runoff, such as discharges from storm water detention basins associated with developments, poses a threat to adjacent bog turtle habitat, as illustrated by a documented case of habitat destruction. A New Jersey bog turtle site was destroyed over the course of four years as water from an upland storm water detention basin was released into an adjacent wetland. The storm water discharge carved a channel through the wetland; modified the site hydrology by removing the surface inundation and many of the spring-fed seeps; and increased the invasion of woody and annual plant species which replaced the sedges and rushes typical of bog turtle habitat. Bog turtles no longer occur at this site.

Development in the vicinity of wetlands also poses a threat when the water table is lowered due to the sinking of wells, or when roads act as barriers to the normal flow of surface water. Urban, commercial, and residential development contribute to increased traffic (leading to increased bog turtle road-kills), surface water pollution, and accelerated succession by invasive native and toxic plant species (due to changes in wetland hydrology, and suppression of natural factors that impede succession).

Untimely mowing or burning and the use of herbicides and pesticides in adjacent agricultural fields also degrade bog turtle habitat. Many wetlands occupied by bog turtles are located in agricultural areas that are subject to frequent livestock grazing. Light to moderate grazing impedes plant succession by minimizing the encroachment of invasive native and exotic plant species. However, heavy grazing destroys bog turtle habitat by cropping and trampling vegetation that is necessary for turtle nesting, basking, foraging, and cover.

The bog turtle is a target for pet collectors due to its rarity in the wild, distinctive coloration, and small size. Take (primarily illegal) both for the national and international commercial pet trade industry has occurred for many years. Collecting is a significant factor in the species decline and is an ongoing threat to its continued existence in the wild. During the last five to ten years, an increasing number of bog turtles have been advertised for sale, and prices have increased substantially. The increase in price most likely reflects the increase in demand for the turtles; the increase in demand increases the threats to the wild populations.

Atlanta Zoo personnel reported that from 1989 to early 1991, over 1,000 bog turtles were exported to Japan. These figures differ significantly from Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) data and represent a significant amount of unreported illegal trade. The World Wildlife Fund has listed bog turtles as among the world's top 10 "most wanted" endangered species. According to Alan Salzburg, President of the American Turtle and Tortoise Society, the bog turtle is considered the most prized turtle in the United States, and when bog turtle locations become publicly known, they are exploited by collectors within one year. Due to the threats facing bog turtle populations, the Society for the Study of Amphibians and Reptiles adopted a resolution calling for the prohibition of collection from wild populations. Due to the small size of existing populations, and the low reproductive and recruitment potential of this species, the removal of even a few breeding adults can do irrevocable damage to a population.

Illegal trade is difficult to detect due to the questionable origin of turtles being offered for sale. Bog turtles are often "laundered" through states which either do not have native populations (e.g., West Virginia, Florida, California), or through states which have inadequate protection of their own bog turtle populations. Hatchling and juvenile turtles marketed as captive-born are usually offspring from gravid adult females illegally brought into captivity and held until they deposit eggs. The eggs are then hatched in captivity, and the captive-born (but not captive-bred) offspring are then marketed or retained.

Bog turtles (particularly the eggs and young) are preyed upon by raccoons, opossums, skunks, foxes, snapping turtles, water snakes, and large birds. Predation by raccoons appears to increase in areas with high human density, since raccoons favor fragmented areas consisting of farmland, forests, and residential development. Predation of eggs and/or hatchlings may play a significant role in reducing the size of the population and skewing its age structure.

Of additional concern is the recent (1997) discovery of Mycoplasma (the bacterium that adversely affects the desert tortoise) at a bog turtle site in New York. This disease has the potential to cause significant declines in bog turtle populations. The site where Mycoplasma has been discovered has been identified as one of the best remaining New York sites and lies in a valley with additional, extant sites leading to the possibility of spread of the disease through a significant portion of the remaining bog turtle range in New York State.

Development and agriculture adjacent to bog turtle habitat can result in soil disturbance and increases in the nutrient and sediment load, thus allowing for the invasion of exotic species such as multiflora rose, purple loosestrife, giant reed, and reed canary grass, as well as native species such as red maple and alder.

Beavers pose a threat to those bog turtle populations that are isolated and/or occur within the only remaining suitable habitat within a watershed. Flooding caused by beavers now poses a threat to three bog turtle populations in Maryland.

Thick deposits of iron bacteria, suggesting possible contamination from pollutants, have been found at three bog turtle sites in Maryland. Reptile and amphibian populations at these sites are much smaller in size than one would expect based on the habitat characteristics. Wetland habitats are also vulnerable to pollutants (oil and grease) carried by storm water runoff. One New Jersey wetland occupied by bog turtles was degraded by trash and motor oil that was carried through a storm drain.

The bog turtle is also vulnerable to local extirpation and range-wide reduction due to: (1) the small size of many populations; (2) the isolation of existing populations; (3) the delay in reaching sexual maturity; (4) low juvenile recruitment rates; and (5) relatively low mobility and small home ranges. Isolation of populations prevents gene flow which can result in an inbred population with low fecundity. Further, isolation and habitat fragmentation prevent recolonization of existing habitat or expansion and colonization into newly created habitats.

Vehicles and livestock pose a direct threat to bog turtles because they can kill and injure individuals. Roads near occupied bog turtle sites contribute significantly to mortality as is evidenced by the number of dead turtles found along roadsides. Roads that are adjacent to or within wetlands pose the greatest threat to bog turtles. Because livestock can trample bog turtles, a large number of livestock within a wetland can pose a threat to the turtle population.

Conservation and Recovery

Bog turtles receive some degree of protection through state listings as endangered or threatened species, and take from the wild within all range states requires a valid permit.

In 1975, the bog turtle was added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, and in 1992 it was transferred to Appendix I. Both import and export permits are required from the importing and exporting countries before an Appendix I species can be transported, and an Appendix I species can not be exported for primarily commercial purposes. These CITES permits are not issued if the export will be detrimental to the survival of the species or if the specimens were not legally acquired.

The Tortoise and Freshwater Turtle Specialist Group of the IUCN recently evaluated the status of the bog turtle. Based on the species' precipitous decline and threats to its continued existence, the bog turtle was included as an endangered species on their 1996 IUCN Red List.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308
http://www.northeast.fws.gov/

U. S. Fish and Wildlife Service
315 South Allen Street, Suite 322
State College, Pennsylvania 16801-4851
Telephone: (814) 234-4090
Fax: (814) 234-0748

Reference

U. S. Fish and Wildlife Service. November 4, 1997. "Final Rule to List the Northern Population of the Bog Turtle as Threatened and the Southern Population as Threatened Due to Similarity of Appearance." Federal Register 62 (213): 59605-59623.