Give Turtles a Brake

Dead gravid female Cooter on north Florida road.

It’s that time of year, maybe you’ve already noticed. Animals are back and moving about and trying to reproduce. But in this age of hundreds of millions of motor vehicles going everywhere at high speeds, anybody who’s slow is vulnerable. And one of the most vulnerable to death on our highways are turtles. No matter how many times I see them crushed and lifeless on a road, it breaks my heart. It must happen hundreds or thousands of times a day in the USA.

Nesting Females: Roads, Roadsides, and Predators

What makes it even worse is that a disproportionate amount of the turtles being killed are adult females. They are especially at risk because of the long distance forays they make searching for nest sites in spring and summer. Some turtles are terrestrial, such as Box Turtles and tortoises, some are amphibious, such as Wood Turtles, but most are aquatic — and they all lay eggs and nest on land, such as roadsides. Even aquatic species such as Sliders and Cooters, and Map, Musk, Softshell, and Snapping Turtles may nest 200-600 yards from the water. When they leave their wetlands in search of upland nest sites, they usually will have to cross at least one road.

Breeding females are the ones most important to sustaining populations and the ones that populations can least afford to lose. Vehicular mortality can cause population declines and roadkill of females during the nesting season can be the most significant threat to population persistence. The mortality to the adults can occur from not just vehicles, but also from the predators such as Raccoons who are attracted to roadsides. These predators also dig up the nests and eat the eggs and the hatchlings. At one place, the proportion of turtle nests lost to Raccoon predation ranged from 63% to 100%, and this was in a “protected” area.

Box turtle.

Population Viability

Most turtle species possesses life history traits that make populations especially vulnerable and sensitive to increased human-caused loss and mortality: slow growth, late maturity, long lives, low reproductive potential (small clutches), and high natural mortality of eggs and hatchlings (such as from predators). Some species, such as the northeast’s Wood Turtle, can take 15-20 years to reach maturity. And then, after reaching maturity, turtles must survive and reproduce for decades more just to replace themselves.

Field studies and statistical analyses clearly show that even modest rates of take (intentional or incidental) of adult or juvenile turtles can lead to strong declines in populations. The loss of a very small number of turtles above natural attrition can be devastating. They may not reproduce enough or survive long enough to make up for the population losses from collection, predation, habitat degradation/destruction, and being killed on roads or by logging or agricultural operations. There are limits to how much cumulative mortality and stress a population can absorb and still be healthy and viable for the long term.

Wood Turtle roadkill on the George Washington National Forest.

Roads and Roadkill

Each and every day in America there are development and commercial activities on the ground, including more roads being built and more drivers using them. Most areas of the East, where most turtle species reside, are already within ca. 400 yards of a road. Not surprising, considering that on the landscape currently occupied by the USA, in 400 years we’ve gone from ZERO to 5-6 MILLION MILES OF ROADS. The ecological effects of roads and/or mechanized use include erosion, air and water pollution, spread of invasive weeds, avoidance of road or machine-affected areas by wildlife, increased access by poachers and common meso-predators (e.g., Raccoons), habitat loss and fragmentation, and massive amounts of roadkill — some estimate 1 MILLION ANIMALS/DAY – and that of course doesn’t include the incomprehensible numbers of invertebrates.

Much of the problem, of course, is not the roads per se, but the vehicles using the roads. Roadkill is exacerbated due to increases in traffic volume. A probability model estimated that the likelihood of a turtle successfully crossing U.S. Highway 27 in Florida decreased from 32% to only 2% twenty-five years later due to a 162% increase in traffic volume.

Passageways and Fencing

The day-in day-out magnitude of the road kill on our nation’s highways is a national disgrace and tragedy. Retrofitting America’s road system to make it more wildlife friendly needs to be a priority for improving our infrastructure; such as installing wildlife crossings — overpasses and tunnels. A new Civilian Conservation Corp could put enormous numbers of people to work accomplishing this necessity.

Identifying hotspots of mortality and installing passageways and fencing can make a huge improvement. Barrier or drift fences with under-highway culverts to provide passageways and prevent animals’ use of roads during dispersal can dramatically reduce roadkill. Along a 0.7-km section of one north Florida highway near Lake Jackson, turtle mortality before installation of the fence was 11.9 turtles/km/day, while post-fence mortality was 0.09/ km/day, a decrease of more than 99%.

Direct Action

Until we systematically mitigate/ prevent/rectify these systemic sources of population decline and extirpation, and even when we do, direct action is essential.

Stopping your vehicle and getting turtles off of roads can make a big difference (I move snakes off the road as well). You can usually do this without compromising your safety. Be gentle and move the turtle in the same direction it was going, as far off the road as you can place it. It doesn’t take up much of your time. And the turtles need all the help they can get. Please help and give them a brake. And encourage your friends and neighbors to do likewise.

 

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