September 29, 2009
How Did the Box Turtle Cross the Road? With a Wildlife Crossing
The HSUS helps box turtles (and other wildlife) on a Maryland road
"Having once performed the spectacular feat of getting its girdles inside its ribs, [the turtle] lapsed into a state of complacent conservatism" and watched as "Eohippus begat Man o' War and a mob of irresponsible and shifty-eyed little shrews swarmed down out of the trees to chip at stones, and fidget around fires, and build atom bombs." —Archie Carr, Handbook of Turtles (1952)
In this seminal book on turtles, Dr. Archie Carr noted that, for 200 million years, turtles have made as few structural compromises as possible, "for by now their architecture and their philosophy had been proved by the eons." Tragically, that architecture and philosophy now threaten many turtle species, including the once common box turtle.
The hard shell that protects plodding, complacent box turtles so effectively from predators offers no defense against SUVs and bulldozers, and as a result, every long-term study conducted on box turtle populations has found that they are declining. According to C. Kenneth Dodd, Jr., author of North American Box Turtles: A Natural History, road mortality is the greatest direct threat to box turtles.
For this reason, The HSUS was particularly interested when we received a call from an employee of Greenbrier State Park in western Maryland. The caller was asking whether The HSUS could do anything to help reduce the number of box turtles killed each summer on a stretch of road near her home. Her request presented a challenge because, while impressive strides are being made in a number of states to alter roads to provide wild animals with a safe passage, these efforts rely on the relatively predictable habitat-based movements of the species in question. The trouble with protecting box turtles is that their movements are so unpredictable.
The trouble with box turtles
Box turtles inhabit woodlands throughout the eastern half of the United States; females venture into open areas to lay their eggs, and males move within their home ranges in search of females. Wherever wooded habitat (and adjacent open fields) and roads intersect, box turtles in the area may attempt a crossing. But where do they cross? Couldn't they cross at any one of thousands of spots along a road? And even if we knew where turtles cross, how do we know what kind of fencing structure to build to protect them? Would the turtles even be willing or able to use it? Thanks to our caller, we thought we could answer the first question—where do turtles cross on the road?—since she had observed an unusually high number of box turtle adults (six) crushed in one section last summer.
At first glance, six turtles may not seem like a significant figure, but the number grows in importance when you take into account that every adult box turtle is vital to the future of its population. Box turtle populations in the fragmented habitats typical of the eastern United States are so sensitive to the loss of adults that, according to modeling studies conducted by Dr. Richard Seigel of Towson University, the loss of just three from a population of 50 males and 50 females could doom that population to a slow, but irreversible, decline to extinction.
Most box turtles never survive the eight or so years that it takes to reach breeding age: Foxes, skunks, raccoons, opossums, crows, turkeys, domestic dogs and cats, and other animals won't hesitate to eat turtle eggs and young turtles whose shells are not yet hard enough to provide much protection. Those turtles who do survive must contend not only with roads, but also with an increasing loss of their habitats to development, which in turn brings more roads, more dogs and cats, and more people who tend to take turtles from the wild, thinking that they will make good pets. Every one of the 50 or so years that a wild female box turtle might live is crucial in ensuring that, of the five or six eggs she may lay a year, at least one of her young survives to adulthood to replace her in the population.
So why not just add turtles from areas where they might be relatively abundant to areas where they are declining? Though that may seem like a solution, box turtles are nature's homebodies. They often spend their entire lives in an area no bigger than a couple of acres, where they know every nook and cranny—where the best spots are for finding food or for water on hot summer days or for safe digs to wait out the long winter months. If taken from their homes and released somewhere else, they use their amazing ability to orient by the sun and the earth's magnetic field to head home, facing all the hazards that such a journey holds. What's more, the genetic and disease implications of moving box turtles around are completely unknown.
That's why the only workable solution to ensure that these reptiles remain a part of our fields and woodlands is to protect their habitats and to eliminate, as much as possible, their death under our tires.
Starting the project
Even before starting our turtle crossing project, we had in our possession one important piece of information: Six turtles died while trying to cross over a relatively short road segment. This indicates a crossing "hot spot" for box turtles, which is unusual. Many turtle species, during breeding season, migrate from water bodies to upland areas to lay their eggs, which makes predicting the general location in which they might cross any roads in their path relatively easy. It is far more difficult to predict where box turtles will want to cross the road because, as terrestrial turtles (those who don't rely on lakes, ponds, or the ocean), they do not home in on bodies of water.
Discovering this crossing hot spot provided us with an excellent opportunity to test our idea. We decided to construct a fence that could funnel turtles into two existing small corrugated metal culverts under the road, which could help the reptiles get to the other side without losing their lives. This was, to our knowledge, the first such attempt to secure safe passage for box turtles.
In early April, as snow flakes filled the air, a crew of volunteers from The HSUS and local herpetological and conservation groups began pounding in the first of many hundreds of stakes to anchor the silt fencing—the black plastic fencing used to control erosion at construction sites. Having obtained permission from the state park, the few private landowners whose property fronted the road section, and the county roads department, we hoped that we could complete the job in a couple of long days.
Since the site is in the foothills of the Appalachian Mountains, the ground is extremely rocky; digging a trench to bury the bottom of the silt fence—to prevent turtles from crawling or digging under it—proved close to impossible. Instead, we used thousands of sod staples to affix the bottom of the fence to the ground, and then pushed soils and leaves on top to deter turtles determined to find a way under. It soon became clear that our goal of finishing in two days was a pipe dream. Four weekends after we started, we were still at it (and still accompanied by snow flakes in this unusually cold spring). Eventually, we erected 1.7 miles of silt fencing to guide turtles to the culverts.
The current thinking on wildlife crossings dictates that structures designed to funnel wild animals under roads should be "high, wide, and handsome," so that animals do not feel confined and are able to easily see what's on the other side. The culverts on our site might best be described as low, dark, and ugly, but at least they seldom carry water, which would deter box turtles from using them. We decided that if box turtles would use these pitiful structures, they would certainly use almost any structure under roads if guided to it by fencing.
We anxiously awaited the development of the first rolls of film from the cameras and detectors we installed in the culverts to monitor their use by turtles. At first—though we got some great photos of rocks, leaves, and the occasional puddle—we were disappointed by the absence of wildlife. But by about the third roll of film, we had corrected some technical problems and began to get wonderful photos of chipmunks, toads, raccoons, and others using the culvert to safely navigate the road. We were pleased, but we asked ourselves, "Where are the turtles?" We began to wonder if the long, dark culverts discouraged use by box turtles, who use the sun to navigate. Just as we’d concluded that the absence of turtle use was nonetheless providing useful information about better ways of helping them navigate roadways, the first photos of turtles in the culverts appeared. Three turtles made use of the culverts the first summer, and several more each year that followed.
This project serves to illustrate how useful existing culverts, bridges, and other structures can be when properly fenced to funnel wildlife to and through them. While not designed for wildlife passage, these structures provide millions of potential safe passageways for small animals.
Update: On the basis of the success of this project, a proposal for federal funding to install permanent fencing and improved culverts was approved by a committee of natural resource and transportation professionals in 2008. Work will begin in 2010, ensuring that box turtles and other wildlife will have an alternative to a dangerous road crossing.
Susan Hagood is a Wildlife Issues specialist for The HSUS. She worked on this box turtle crossing project.