As the human population density increases, the natural beauty and integrity of any area will soon decline. The construction and transportation infrastructure necessary to accommodate a large increase in human density have several inevitable impacts on wildlife. Habitat alterations and road-kill can potentially claim a large number of animals every year in suburban regions or force them to relocate. As an area is fragmented and food, shelter, and mates become scarcer and farther apart, it becomes increasingly difficult for populations of some species to maintain their viability, while others thrive. Common "weedy" species are often favored in suburban areas, as they are typically well adapted to human disturbance, even benefiting from our presence. Many human-tolerant scavengers and opportunistic generalist predators can out-compete less tolerant animals for resources, and often prey on their eggs and young. Thus the ecological integrity of an extensively developed area is eroded as the less common species are replaced by common ones.
One animal that is especially sensitive to increases in human density is the turtle. Turtles are slow moving, require several years to reach sexual maturity, and the eggs and young are extremely vulnerable and highly palatable to predators. The life-history traits associated with longevity also makes turtles ill-adapted to a sudden increase in mortality (2, 6). To complicate matters, demographic studies for many species of turtles are difficult to undertake and require several years to get accurate information. Unlike the common Eastern Painted Turtle, which prefers open ponds and rivers, species such as the Spotted Turtle and the Eastern Box Turtle inhabit less visible places such as heavily vegetated stream corridors, freshwater marshes, and upland forest. These animals are often difficult to find and to track, especially the juveniles. Animals must be trapped, marked, and monitored over several years to determine population parameters and trends for a given area. The time needed to conduct turtle demography studies is often much too long for the effective and rapid results required to provide protection for threatened populations.
CAUSES of DECLINE in TURTLE POPULATIONS
It is believed that turtle populations in general are currently in decline throughout New England (26, 28). More than one third of the turtle species in the United States are in need of conservation action (14), as a result of a clash between the turtles' ecological requirements and a number of direct and indirect human impacts of varying nature and intensity.
Biological and Ecological Factors
Several aspects of their biology and ecology impose limitations on the turtle’s ability to cope with the impacts of human presence. In combination, these factors make small populations especially vulnerable to catastrophic losses.
Slow reproduction. Female turtles can take from 5 to 15 years to reach sexual maturity (8). The Eastern Box Turtle produces an average of only four or five eggs in each clutch, with one or two nesting events per year (27). Low rates of reproduction coupled with increased adult and juvenile mortality make small, isolated populations especially vulnerable to catastrophic losses.
Travel to nesting areas. The nesting habits of most turtle species expose numbers of individuals to high risks. The females often must travel to find a suitable nesting site, which may be a fair distance from their feeding and living quarters. They can travel considerable distances during nesting season, sometimes more than a kilometer from their usual home range (8). The process of getting to a site often necessitates the crossing of roads, parking lots, hayfields and lawns, which often results in human-related mortality.
Limited nesting site availability and high site fidelity. Suitable nesting habitat is thought to be the major limiting factor in the distribution of the diamondback terrapin (19), and this is likely true for other species. Site fidelity was found to be high in many studies (8, 11), thus alterations on important nesting grounds and surrounding areas could have serious implications for local turtle populations.
Low nest success. Like most reptiles turtles need sunlit, open spaces to deposit their eggs. The exposed nest sites often leave hatchlings highly vulnerable to natural predators, household pets, and pet collectors. In rural and suburban areas nesting female turtles frequently utilize hayfields and construction sites (8, 22), which can lead to eggs and young to be crushed by heavy machinery. As ideal nesting areas become more difficult to find or access, the nests tend to be located closer together, further increasing depredation pressures.
Nest depredation was found to be significantly high in several studies (8, 11, 24). Although juvenile mortality in long-lived organisms such as turtles is typically known to be low, Wilbur (29) estimated mortality between hatching and one year of age in a population of Eastern Painted Turtles to be as high as 92%. From a demographic study on a population of snapping turtles in Canada, it was estimated that there were as few as two recruits per year (2). Juvenile mortality is naturally high for some turtles due to heavy depredation in the more vulnerable life stages, further exacerbated by an over-abundance of human-tolerant predators.
Homing tendency. Many turtles display a natural homing capacity. Captured wild box turtles that were released after a short period of time have been known to attempt return to their origin (8, 17). This would make it difficult to relocate turtle populations from areas undergoing development as an attempt to mitigate the impacts on wildlife.
Direct human impacts
Loss of habitat. Presently more than 16,000 acres of forest and farmland are converted to lawns, buildings, parking lots, and roads every year in Massachusetts (25). In a review of threats to imperiled species in the U.S., habitat loss was the leading cause of endangerment (30). Several forest-interior bird species have shown significant declines over the last few decades (23), and this trend is particularly evident in the northeast (13). The most stringent protection measure for wetland buffer zones in the U.S. (100 feet in Massachusetts) was found to encompass less than 50 percent of the turtle nesting sites associated with a wetland in a study done in the southeastern U.S. (3).
Automobiles and heavy machinery. Automobile traffic on back roads presents an obvious and continual threat to terrestrial turtles that are moving about looking for mates and food resources. Nesting habits of aquatic species usually involve overland travel, often resulting in high mortality for gravid females in areas with heavy automobile traffic (10). Also, aestivating and hibernating turtles are often difficult to see in their natural environment, and are easily overlooked by operators of bulldozers and other heavy equipment.
Recreational activities. Fishing and boating. Turtle mortality is likely much higher in areas where fishing, and especially motorboats, are allowed. Turtles often take baited hooks from fishing lines (8, 22), and the bony structure of the mouth makes it difficult to remove barbed hooks. Survey work done in 100-Acre Cove in Rhode Island (11) and Lake Conway, Mississippi (1) showed that injuries from boat propellers were a significant cause of mortality for resident turtles.
Off-road vehicles. During nesting season, female turtles are often found in open sandy places that are also attractive to operators of recreational off-road vehicles. The recent reopening of trails to motorbikes in Myles Standish State Park in Plymouth is a particularly good example of the clash between humans and turtles. Even mountain bikes are a significant threat to turtles as the heavily used trails can act as death traps, tempting nesting females to lay their eggs in the eroded soils in high-traffic areas.
Indirect impacts
Excessive depredation. Wild animals that thrive near human habitations, such as coyotes, raccoons, skunks, gulls, and crows, consume a significant proportion of turtle nests and young (8, 24). It is likely that domestic and feral cats and dogs are also a significant cause of mortality in suburban areas.
Chemical pollutants. Pesticides can potentially reduce food resources for turtles, which eat mainly invertebrates. Also, production of the neural enzyme Cholinesterase is inhibited in many vertebrates by exposure to some commercial pesticides (20).
SPECIES REVIEW
Species of Special Concern
Eastern Box Turtle Terrapene carolina carolina
Box turtles are most threatened by human encroachment. They are mainly terrestrial, and require relatively low-disturbance areas for foraging, finding mates, aestivating, and hibernating. Forests, old fields, and meadows are vital to box turtles as they provide an abundance of food resources such as mushrooms, insects, and berries (8), as well as nesting sites.
There is a small population existing in Norwell in the town-owned conservation area known as Stetson Meadows (16, 22). The parcel was originally purchased for the construction of a golf course in 1972, which was defeated twice by town vote. It is likely that there are other relatively undiscovered populations of box turtles in the surrounding areas, which would be of considerable importance for conservation of genetic variability.
Spotted Turtle Clemmys guttata
These shy turtles inhabit wetlands, cranberry bogs, and swamps. They emerge from hibernation relatively early compared to most other local species, and aestivate through much of the summer. A study conducted in cranberry bogs in Manomet revealed that turtles in the first few year classes were rarely encountered, which may indicate that either breeding has been reduced or the young turtles are simply going elsewhere until they mature (20).
A small pond in Wompatuck State Park was known to have spotted turtles frequenting it year after year, but none have been found been there since 1975 by the same observers (22) despite more than two decades of looking. However, a newly emerged hatchling was found in October 1997 on a mountainbike trail nearby, indicating the presence of at least one breeding pair in the area. Spotted turtles were also found on the property formerly known as the Weymouth Naval Air Station, bringing redevelopment issues to the forefront of the local news.
There are records of more than 300 adult Spotted Turtles in Massachusetts south of Boston (18), possibly qualifying it to be removed from the state list of threatened species. However, this finding does not reflect an accurate estimate of previous population levels, and may lead to underestimation of any actual decline in the population over the next few years.
Plymouth Red-Bellied Slider Pseudemys rubriventris
The slider's total range is limited to an area surrounding Chesapeake Bay, and Plymouth County MA (5). In Massachusetts this species is found chiefly in Coastal Plain ponds, which is a globally unique habitat restricted to a few places in eastern U.S. and Canada (12). There is a high concentration of Coastal Plain ponds in Plymouth, and they are presently under threat from increasing residential development. Excessive water draw-down for municipal purposes can be potentially destructive to the flora and fauna of these fragile systems, which are adapted to the natural cycles of flooding and receding water levels.
The Slider has received much attention over the last few years, and a recovery plan is now in place in Plymouth by the Massachusetts Division of Fisheries and Wildlife that includes egg incubation and headstarts for juveniles. However, headstart programs are viewed by some biologists as an ineffective method of conservation (6). More measures need to be taken to preserve the adults and their habitat as well.
Diamondback Terrapin Malaclemys terrapin
This species inhabits coastal marshes and stream corridors, and in Massachusetts its range is more or less restricted to Cape Cod (5, 21). Heavy residential development pressures on the Cape over the last three decades have threatened the small remnant populations of these turtles (21). In Rhode Island, this species was placed on the state Endangered Species list recently, as they are disappearing from their usual habitat (24). A recent study in New Jersey found that a large number of female Diamondback Terrapins were being decimated on a highway that intersected the route from their living habitat to a nearby nesting area (32).
Common Species
Only three turtle species found in eastern Massachusetts are not on the list of threatened species. The first two are commonly seen in the open, but the Stinkpot, or Musk Turtle, is less common and rarely seen. A few of the latter are known to occur in the upper Indian Head River, and have been captured in the past from ponds in Plymouth County (22).
Eastern Painted Turtle Chrysemys picta picta
Although quite common and tolerant of much human activity, painted turtles are not immune to the destructive actions of humans. Roads that separate ponds and wetlands from upland nesting areas are often littered with turtle remains during the nesting season (8, 22).
Snapping Turtle Chelydra serpentina
Adult snapping turtles are often thought to be dangerous, and pose a minor threat to small children and pets if approached. They are occasionally found in swimming pools and backyards during the nesting season in June and July. Individuals can live up to 40 years or more (9), and females have been known to use the same nesting area year after year despite landscape alterations by humans (22). Less tolerant landowners are likely to have the turtles removed or killed.
Stinkpot (Common Musk Turtle) Sternotherus odoratus
The stinkpot is a fairly common but elusive turtle, preferring slow-moving rivers and shallow ponds. It feeds largely on benthic invertebrates, especially molluscs (8), thus making it exceptionally susceptible to the bioaccumulation of toxins where present.
CURRENT CONCERNS
Transportation "improvements"
Route 3 in Rockland: The decommissioned Weymouth Naval Air Station is slated for the construction of a large shopping mall and commercial complex. A new highway access road will bisect a significant area of forested habitat, and a stream corridor. Both Clemmys guttata and Terrapene carolina carolina are known to inhabit the area (Parsons, M.), and a survey should be done before any construction begins.
Route 44 in Plymouth. Proposed growth in the town of Plymouth will necessitate an improvement of roads for ease of access to and from the expressway. Route 44 is slated for rerouting and widening, as this is a major connecting route to Rt 495 and Rt 3. The new road will span about three miles of what is presently unimpacted wetland area. Several species of turtle including Clemmys guttata and Pseudemys rubriventris inhabit the area.
New Bedford-Fall River Rail Extension. The MBTA is planning an extension of the existing railroad through the towns of Attleboro, Easton, and Taunton. Construction of the rail and additional filling of wetlands may have adverse impacts on the turtle populations in the area. The proposed extension carves through several miles of low-density residential area. This will likely be followed by additional pressures from increased development due to improved access to and from nearby urban regions.
Land-use conversion
Stetson Meadows, Norwell. In 1997, the recreation department proposed the installation of playing fields on approximately 20 acres of the upland portion of the property, where the turtles have been sighted on several occasions (22). In 2000 a town cemetery was proposed for the same site. It was recently discovered that the turtles are nesting in the small grassy field that is used as a parking lot for visitors’ automobiles. Users of such areas, and local residents in general, need to be made aware of the habits of these animals in order to prevent permanent losses. One suggestion is to construct a kiosk at the entrance to the lot with photos and information on box turtles, explaining the situation to new visitors.
Hundreds of housing developments are presently being planned throughout Plymouth County, and the number of new proposals increases each year. New roads will provide access to presently undeveloped areas, opening up more opportunities for local human population growth and suburban sprawl. Two recently proposed land transactions in southern Plymouth County will soon convert more than 12,000 acres of forest and fields into housing and recreational facilities, roads, and commercial centers.
A FUTURE for TURTLES?
Conservation
Several measures can be taken to help reduce turtle mortality in developing areas, including the establishment of "turtle highways" and "wildlife underpasses". Such technology has been implemented in heavily impacted areas of western Europe with some success. We need to consider our options in civil planning and resource conservation if we are to preserve our natural heritage for future generations.
Movement corridors. Establishing connectivity between living and nesting areas, and between other nearby turtle habitats is essential for the survival of turtles. Culverts passing under roads that separate ponds from their inlet and outlet streams, and from known nesting areas, should be designed to accommodate passage for turtles and other animals. Small bridges that allow animals to pass under the road rather than over it could be built in new developments, and eventually replace old culverts.
Protection of nesting areas. Nesting sites that attract large numbers of turtles should be well marked and protected from development and high impact uses. Since many turtles have been known to reuse the same areas year after year, these could be designated as turtle conservation areas.
Limitations on use of chemicals. The springtime activity of females and fall hatching brings turtles into fields, lawns, and gardens where they are exposed to many kinds of toxins. During nesting season, pesticides and fertilizers should not be used near ponds, wetlands, or streams.
Exclusion of motorized vehicles. Motor boats should not be allowed in upper reaches of rivers where turtle populations are large. For example, in the lower Indian Head River where the water is fresh, many turtles can be found in the channel (22). To prevent accidental turtle deaths, motor boats should be excluded in sensitive upriver areas.
Demographic studies. There is a tremendous need to assess turtle populations and establish demographic models in order to understand and control the damages imposed by man (7, 14). Movements, population sizes and natural fluctuations, and habitat requirements need to be thoroughly examined on a local and regional basis.
If it does happen in the near future that large-scale changes of the Earth’s environment, such as global warming, do cause significant climate shifting, it may be necessary to accommodate new species in some areas as their ranges move northward. Thus it would be wise to consider conservation measures that accommodate a number of species that may not presently be in the immediate area.
Research efforts and organizations
There are several organizations throughout Massachusetts actively researching turtles and their habitats, population trends, and conservation measures. To learn more about turtles in your area, report sightings, or help to protect them now and in the future, contact the following organizations:
Massachusetts Natural Heritage and Endangered Species Program. Division of Fisheries & Wildlife, Route 135, Westborough, MA 01581. The program can be reached by telephone at (508) 792-7270 x200, or by fax at (508) 792-7275. http://www.heritage.tnc.org/nhp/us/ma/
A database has been established for a large assortment of species by the NHESP. There are forms available for many species, which can be filled out and returned with information on sightings in Massachusetts.
Massachusetts Audubon Society. 208 Great South Road, Lincoln MA, 01773
Telephone (781) 259-9500.
Herpetologist Tom Tyning is tracking reptiles throughout Massachusetts, including small rattlesnake populations which are threatened with extirpation.
University of Massachusetts in Amherst, Department of Forestry and Wildlife Management. GIS studies of turtle populations throughout New England are being conducted.
The Nature Conservancy.
TNC has published a book entitled "Our Endangered Heritage" that covers many of the threatened and endangered species in the northeast, and features the Eastern Box Turtle.
Manomet Center for Conservation Sciences. P.O.Box 1770, Manomet MA, 02345.
Researchers at the Manomet Center are conducting studies of the effects of cranberry agriculture on Spotted Turtles. Cholinesterase levels are tested by taking blood samples from captured wild turtles that inhabit cranberry bogs, giving researchers some insight into the effects of pesticide use in wetland areas.
New England Wildlife Center.
Located in Hingham, MA this non-profit organization helps injured and displaced wild animals, and also runs educational seminars and volunteer programs.
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