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Understanding Road Mortality Impacts to Salamanders

spotted salamanger

Researchers from the USGS Amphibian Research and Monitoring Initiative have begun a project in collaboration with the National Park Service and the Mississippi Natural Heritage Program to better understand the impact of road mortality to a population of salamanders living along the Natchez Trace Parkway near Jackson, Mississippi. Several species of salamander occur in the area and hundreds of individuals cross the road during annual breeding migrations in the fall and winter. These road crossings make the salamanders vulnerable to mortality from vehicles using that portion of the Parkway. The team will monitor salamander movements to determine the effect of road mortality on the long-term survival of the population.

The Natchez Trace Parkway is a 444 mile two-lane road operated and maintained by the National Park Service. The Parkway crosses three States as it meanders from Natchez, Mississippi towards Nashville, Tennessee. With the completion of a final segment in 2005, traffic increased along a two-mile segment west of Jackson, Mississippi between mileposts 85 and 87. Along with the additional vehicular traffic, NPS personnel noticed that spotted salamander casualties increased.

salamander crossing a road salamander eggs

The salamanders migrate during their annual breeding season between November and April. They leave the terrestrial habitat where they live for the majority of the year, and attempt to cross the Parkway to reach their breeding pools on the opposite side. There, the amphibians lay their eggs and look for food before beginning the return trip home. Because these tiny wildlife are difficult for motorists to see, especially during rainy nights, the Park Service activates flashing signs and reduces the speed limit during this time to encourage motorists to slow down for salamanders. Though mortality has been documented yearly since 2006, this is the first study that directly investigates the impact of road mortality on the health and viability of the spotted salamander population in this area.

drift fencesalamander pitfallSalamanders are captured for monitoring using a method called a drift fence. The drift fence is made of 2 ft. tall woven nylon silt fencing. Plastic buckets are buried at the ground level along the fence every 30 to 45 feet to make pitfalls that capture salamanders. One drift fence is placed along the road where salamanders are known to cross, while another is placed around the pond. Salamanders encounter the fence as they are migrating to or from the pond, but they cannot climb over it. As they walk along the fence, they fall into the pitfalls. The pitfalls are checked several times a day so that the time the salamanders are disturbed is minimalized.

weighingAll salamanders captured at the fences are measured for length and weighed on a digital scale. Each salamander is photographed and the sex is determined. The salamanders are then marked using a fluorescent visual implant elastomer designed for marking animals. The colors and the locations of the elastomer injection make a combination that allows scientists to know which fences the salamander has previously crossed.

This study will allow scientists to estimate the number of salamanders crossing the road and the proportion successfully making the return trip to the upland habitat. This information is necessary to assess the impact of potential road mortality on the salamander population. These data will allow the Park Service to determine the need for mitigation as part of their mission to preserve unimpaired the natural resources of the park system.

injecting markermarker

Additional Resources

Glorioso, B.M., Waddle, J.H., and Hefner, J., 2012, Ambystoma maculatum (spotted salamander): Herpetological Review, v. 43, no. 4 (December), p. 627-628.

Muths, E., Adams, M.J., Grant, E.H.C., Miller, D., Corn, P.S., and Ball, L.C., 2012, The state of amphibians in the United States: U.S. Geological Survey Fact Sheet 2012–3092, 4 p.

Waddle, H., 2011, Amphibian monitoring in the Atchafalaya Basin: U.S. Geological Survey Fact Sheet 2011-3056, 4 p.


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