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, Vehicles, 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
longer 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. Even aquatic species such as Sliders and Cooters, and Map, Musk, Softshell, and Snapping Turtles may nest 200-550 yards from the water [2,3]. When they leave their wetlands in search of upland nest sites, they usually will have to cross at least one road.
In addition, roadsides generally fabricate the environmental conditions sought by female turtles for their nests – open canopy, short or sparse ground vegetation, and friable soil . They are attracted to roadsides for foraging and basking also. But though the physical conditions may be favorable, such sites also incur increased mortality.
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 [5,6]. 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 .
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) [8,9]. 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 [10,11,12].
For turtles there is no apparent “density dependent” response operant ; i.e., at low population densities there is no compensatory increase in birth rate or hatchling survival. In fact, just the opposite can reasonably be expected to occur in low populations — decreases in birth rates, due to such factors as difficulty in finding mates , resulting in further reductions in population size.
Field studies and statistical analyses clearly show that even modest rates of death or removal (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. Turtles 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 absorb and still be healthy and viable for the long term.
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 for 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% in 1977 to only 2% in 2001 due to a 162% increase in traffic volume .
Passageways and Fencing
The staggering magnitude of the day-in day-out road kill on America’s highways is a national disgrace and tragedy. Retrofitting the nation’s road system to make it more wildlife friendly needs to be a priority for improving our infrastructure; such as installing fencing and 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 reduction of more than 99% .
Until we systematically mitigate/ prevent/rectify these systemic sources of population decline, extirpation, and extinction – 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 family, friends and neighbors to do likewise.
1. Steen, D.A., J.P. Gibbs, K.A. Buhlmann, J.L. Carr, B.W. Compton, J.D. Congdon, J.S. Doody, J.C. Godwin, K.L. Holcomb, D.R. Jackson, F.J. Janzen, G. Johnson, M.T. Jones, J.T. Lamer, T.A. Langen, M.V. Plummer, J.W. Rowe, R.A. Saumure, J.K. Tucker, and D.S. Wilson. 2012. Terrestrial habitat requirements of nesting freshwater turtles. Biological Conservation 150: 121-128.
2. Sterrett, S.C., L.L. Smith, S.W. Golladay, S.H. Schweitzer, and J.C. Maerz. 2011. The conservation implications of riparian land use on river turtles. Animal Conservation 1: 38-46.
3. Refsnider, J.M. and M.H. Linck. 2012. Habitat use and movement patterns of Blanding’s Turtles (Emydoidea blandingii) in Minnesota, USA: A landscape approach to species conservation. Herpetological Conservation and Biology 7: 185- 195.
4. Kolbe, J.J., and F.J. Janzen. 2002. Impact of nest-site selection on nest success and nest temperature in natural and disturbed habitats. Ecology 83: 269-281.
5. Crawford, B.A., J.C. Maerz, N.P. Nibbelink, K.A. Buhlmann, and T.M. Norton. 2014. Estimating the consequences of multiple threats and management strategies for semi- aquatic turtles. Journal of Applied Ecology 51: 359–366.
6. Steen, D.A., M.J. Aresco, S.G. Bielke, B.W. Compton, E.P. Congdon, C.K. Dodd Jr., H. Forrester, J.W. Gibbons, J.L. Greene, G. Johnson, T.A. Langen, M.J. Oldham, D.N. Oxier, R.A. Saumure, F.W. Shueler, J.M. Sleeman, L.L. Smith, J.K. Tucker, and J.P. Gibbs. 2006. Relative vulnerability of female turtles to road mortality. Animal Conservation 9: 269-273.
7. Browne, C.L. and S.J. Hecnar. 2007. Species loss and shifting population structure of freshwater turtles despite habitat protection. Biological Conservation 138: 421–429.
8. Gibbs, J.P. and G.D. Amato. 2000. “Genetics and Demography in Turtle Conservation”, pp. 207-217 in M.W. Klemens (ed.), Turtle Conservation. Smithsonian Institution Press, Washington D.C. 334 pp.
9. Heppell, S.S., H. Caswell, and L.B. Crowder. 2000. Life histories and elasticity patterns: Perturbation analysis for species with minimal demographic data. Ecology 81: 654-665.
10. See “feasible demography” in Seigel, R.A. 2005. “The importance of population demography in the conservation of Box Turtles: What do we know and what do we need to learn?”, pp. 6-7 in C. Swarth and S. Hagood (eds.), Summary of the Eastern Box Turtle Regional Conservation Workshop. Humane Society of the United States, Washington, D.C.
11. Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1993. Delayed sexual maturity and demographics of Blanding’s Turtles (Emydoidea blandingii): Implications for conservation and management of long-lived organisms. Conservation Biology 7(4): 826-833.
12. Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1994. Demographics of common Snapping Turtles (Chelydra serpentina): Implications for conservation and management of long-lived organisms. American Zoologist 34: 397-408.
13. Belzer, W. and S. Seibert. 2009. How do male box turtles find mates? Turtle and Tortoise Newsletter 13: 11–21.
14. Reed, R.N. and J.W. Gibbons. 2003. Conservation status of live U.S. non-marine turtles in domestic and international trade. Report to US Department of the Interior and US Fish and Wildlife Service. 92 pp. Accessed at www.tiherp.org/docs/Library/ Turtle_trade_report.pdf
15. Riitters, K. and J. Wickham. 2003. How far to the nearest road? Front. Ecol. Environ. 1: 125–129.
16. Aresco, M.J. 2005. Mitigation measures to reduce highway mortality of turtles and other herpetofauna at a north Florida lake. Journal of Wildlife Management 69: 549–560.