Road Mortality: What we can do about it

Dead Glass Lizard (Ophisaurus sp.) hit by a car

Driving around the Naples area, it’s hard to go 5 minutes without seeing a dead animal on the highway. Reptiles, amphibians, birds, rabbits, and even the rare Florida Panther (Puma concolor coryi) are the unlucky victims of a fragmented habitat that in the best case inhibits natural movement and gene flow and at worst kills an animal trying to travel between suitable habitats. Numerous studies have looked at the effects of road mortality on various species in Florida, with a variety of concerning findings.

One study conducted over a 2-year period (1987-1989) reported encountering 1,018 snakes on an 11.3km road segment, 70% of which were found dead or injured by cars (Bernardino & Dalrymple, 1992). Another study, by Steen et al. 2006, reported that female turtles are more likely to cross roadways than males and therefore experience higher road mortality, potentially skewing sex ratios near roadways and leading to population declines. From 1979-1991, 32 Florida Panther deaths were recorded, with the most common cause (15, 46.9%) being road mortality (Maehr, Land & Roelke, 1991). This is just a small sample of the literature regarding road mortality, but it is apparent that regardless of the species or location, the intersection of wildlife and vehicles never bodes well for the wildlife.

Eastern Corn Snake (Pantherophis guttatus) basking in the road

So what can be done to reduce the threat of road mortality on wildlife populations? Various mitigation approaches are used, including motorist behavioral modification (speed limits, signs, lights) and animal behavioral modification (wildlife crossing structures, habitat alterations). Wildlife crossing structures include underpasses, overpasses, drift fences, exclusion fences, and culverts, to name a few. Each mitigation approach has its pros and cons, and determining the most effective strategy requires extensive research and monitoring of wildlife populations and causes of unnatural mortality. Location, structure dimensions, habitat cover, noise levels, the use of fencing, and many other factors can determine the success or failure of a crossing structure. To learn more, check out the papers referenced below (Foster & Humphrey, 1995; Dodd, Barichivich & Smith, 2004; Glista, DeVault & DeWoody, 2009).   

References

Bernardino Jr F, Dalrymple G. 1992.Seasonal activity and road mortality of the snakes of the Pa-hay-okee wetlands of Everglades National Park, USA - ScienceDirect. Available at https://www.sciencedirect.com/science/article/abs/pii/000632079290928G (accessed December 9, 2018).

Foster M, Humphrey S. 1995. Use of Highway Underpasses by Florida Panthers and Other Wildlife on JSTOR. Wildlife Society Bulletin 23:95–100.

Glista DJ, DeVault TL, DeWoody JA. 2009. A review of mitigation measures for reducing wildlife mortality on roadways. Landscape and Urban Planning 91:1–7. DOI: 10.1016/j.landurbplan.2008.11.001.

Dodd C, Barichivich WJ, Smith LL. 2004. Effectiveness of a barrier wall and culverts in reducing wildlife mortality on a heavily traveled highway in Florida. Biological Conservation 118:619–631. DOI: 10.1016/j.biocon.2003.10.011.

Maehr D, Land E, Roelke M. 1991. Mortality patterns of panthers in southwest Florida. Proceedings of Annual Conference of Southeastern Fish and Wildlife Agencies 45:201–207.

Steen DA, Aresco MJ, Beilke SG, Compton BW, Condon EP, Dodd CK, Forrester H, Gibbons JW, Greene JL, Johnson G, Langen TA, Oldham MJ, Oxier DN, Saumure RA, Schueler FW, Sleeman JM, Smith LL, Tucker JK, Gibbs JP. 2006. Relative vulnerability of female turtles to road mortality. Animal Conservation 9:269–273. DOI: 10.1111/j.1469-1795.2006.00032.x.

- Randi Bowman, Research Intern