Species and Sprawl: Wood Turtles
F15 has no tail, only three legs, and a transmitter with a 30 cm long antenna epoxied to her back. Considering F15 is a turtle—and one who must regularly cross a well-trafficked country road to find food and lay her eggs—missing a foot sounds like a cruel twist of fate.
But F15’s battle scars are par for the course. After all, at possibly 50 or 60 years old (in both people and turtle years), she’s been through her share of raccoon sneak attacks and near-misses with plough blades in her habitat—the streams, hayfields, woodlands, and backyards of the rapidly suburbanizing, formerly agricultural Connecticut River valley.
Mike Jones, a biology graduate student at the University of Massachusetts at Amherst, has been following F15 and 52 of her shelled compatriots in the most comprehensive study yet of the habitat use and range of Clemmys insculpta, or wood turtle. The species is of conservation concern in Massachusetts and most of the 16 U.S. states and 4 Canadian provinces it calls home. For the last nine months, Mike has been tracking F15’s whereabouts twice a week via radio transmitter. And he can tell you, unequivocally, that she has not been flattened by an SUV. Yet.
“The new homes, businesses, and malls that we associate with urban sprawl are connected via roads,” says Paul Sievert, a U.S. Geological Survey ecologist and lead researcher on the wood turtle study. “This fragments the habitat into smaller pieces and increases the traffic rate on the roads currently in existence. There’s not enough time for a turtle to cross the road.”
The research is intended to provide a clearer picture of how much and what kind of space wood turtles need to survive, and to determine whether existing populations can surmount pressures from sprawl and persist in perpetuity. Jones’s and Sievert’s work will eventually guide a Division of Fisheries and Wildlife conservation plan to protect wood turtle habitat in Massachusetts, a state with some of the tightest environmental laws in the country.
Keep on Truckin’
In less than a hundred years, wood turtles have dwindled from common to fairly scarce in their historic range, which spans the Great Lakes region, New England, and southern Canada. “In New England in the 1800’s, people recorded that they went out with their horse and buggy, and in an afternoon picked up a hundred wood turtles,” says Sievert. “Fast-forward to today. If you find a wood turtle at all, it’s usually a road-killed wood turtle.”
Wood turtles spend most of their days swimming in, basking in, and exploring one cold, brisk stream for their entire lives. The study area in this case is the headwaters of one of the Connecticut River’s 38 main tributaries. Still, the reptiles leave the river regularly to forage for amphibian eggs at vernal, or temporary, pools in adjacent woodlands or to lay eggs in warm, sandy upland sites.
To trail the exact moves of each turtle, Jones uses dental acrylic to affix a transmitter and coiled antenna onto the shell. He programs a handheld receiver to pick up each turtle’s personal signal. Suited in fisherman’s waders and paddling a canoe, Jones relocates each turtle about twice a week during the spring, summer, and fall, noting its GPS location, surrounding habitat, and behavior. “Eventually we’ll be able to measure each turtle's habitat selection on a very large scale,” he says.
It's Not Easy Being Green. Er, Brown and Orange.
During their meanderings, turtles are almost sure to encounter a road, or two, or three. That’s because humans like to build roads parallel to river edges, as construction is much easier along flat riverbeds. Turtles often travel perpendicular to rivers, which usually entails dodging tires.
While roads affect many species, this geometry can be especially devastating for some reptiles, which bank on the high survival rate of adults, rather than juveniles, to maintain their populations. Unlike the super-fecund hare, female wood turtles lay just a single clutch of about 10 eggs a year. Only a small percentage of the eggs hatch, and only a fraction of the hatchlings endure the dangers of raccoons and tractors and tarmac to reach adulthood at age 17. These survival odds, plus the fact that turtles have an impressive number of potential breeding years (some can live over a century) mean that adult turtle loss can seriously affect a species. “One study predicted that if two turtles were lost from a population annually,” says Jones, “the whole population would be lost in less than a hundred years.”
To compound the problem, Jones has learned that females ramble much greater distances from the river than do male turtles—sometimes 500 m to either side. Females, then, are more likely to encounter a road, which suggests that they are dying at a much faster rate than males. “Which is terrible,” says Jones. “You could keep a population around with fewer males for much longer than you could with fewer females.”
Unfortunately, human pressures—and fancies—take their toll on turtles in ways other than vehicular, namely via the pet trade. Wood turtles are particularly noted for their personality (In 1952, landmark herpetologist Archie Carr wrote in hisHandbook of Turtles: “For all who have kept them are agreed that the wood turtle makes a better pet than any other [turtle] species.”). Today, however, capturing wild turtles as pets is illegal throughout the country.
Still, “poaching of turtles for the pet trade and collection of animals by recreationists continues to remove wood turtles from the wild,” says Sievert. “This can decimate local populations.” The effect on the population is exactly the same as if the turtle were killed on a highway.
What’s Around the Bend?
“Many people are convinced that the ideal situation is to have their home out in the woods,” says Sievert. “But if wildlife had a vote, they’d choose for humans to stay concentrated in urban centers rather than spreading ourselves out in a sprawling suburban environment.”
Sievert suggests that one long-term solution for the reduction of sprawl and its impact on wildlife would be for human population growth to reach zero. In the meantime, wise planning that incorporates the needs of wildlife—such as state-driven land purchasing, conservation easements, mitigation measures like road underpasses for turtle travel, or limiting development—could go a long way in reducing animal mortality and increasing population viability for threatened species in the United States.
Jones adds that the fate of wood turtles is representative of the fate of many creatures in wetland habitats, which are under particular attack by sprawl. “This species was clearly meant to be present throughout New England,” he says. “That was the case for probably the last six or eight thousand years. They have the right to go on existing here.”
US Geological Survey
The Wood Turtle: A Natural History
Reptile and Amphibian Underpasses
World Wildlife Fund: Reptile Trade
More About This Resource...
Our innovative Science Bulletins are an online and exhibition program that offers the public a window into the excitement of scientific discovery. This essay was published in February 2005 as part of the Species and Sprawl: A Road Runs Through It Bio Feature.
- It opens with the story of F15, one of the battle-scarred wood turtles being studied in the most comprehensive study yet of the habitat use and range of Clemmys insculpta.
- It then details what scientists are learning about how much and what kind of space wood turtles need to survive, and whether they can surmount pressures from sprawl.
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Working individually or in small groups, have them visit the Federal Highway Administration's Critter Crossings: Linking Habitats and Reducing Roadkill website and report on some of the methods being used to protect wildlife along highways.