Herps

When considering roads, reptiles and amphibians suffer similar effects from the construction, existence, and expansion of roads. Roads and highways have taken an enormous and largely unnoticed toll on these species, but we are finally learning how to minimize and mitigate the impacts.

Herps are ectotherms, meaning their body temperature and metabolism are regulated by ambient temperature. As such, herps are particularly attracted to warm surfaces where they can raise their body temperature -- including roads and highways. Anyone who has ever stepped on a blacktop road in the middle of summer has experienced the "heat island" effect, where a noticeable change in temperature is retained in a small area. Even unpaved roads are warmer than the surrounding area if trees have been cleared from the right-of-way, allowing direct sunlight to the road surface. Reptiles such as snakes are especially likely be killed while basking on road surfaces.

Also, amphibians such as frogs and salamanders are attracted to pools of water that collect adjacent to roads from storm events. In undisturbed habitats, many amphibians depend on seasonal pools for reproductive purposes. Along roads, these pools can essentially act as traps. During storm events, roadside drainage ditches contribute sedimentation and high velocity surface flow washing off of roads, contaminating and speeding up the flow of waters used for reproduction. Furthermore, roadside waters tend to evaporate relatively quickly which can result in the dessication of eggs laid by amphibians before they hatch and the trapping of developing young

Even for the most mobile herps, roads are a difficult barrier to navigate. Even at speeds as low as 25 miles per hour, most herps are unnoticeable to drivers. Snakes, turtles, and frogs are the herps most commonly killed by vehicles. For other, less mobile herps, roads can act as unpassable barriers. Some species of salamanders will not even attempt to cross a dry road because their skin must remain moist. Those who do may dry out or be hit by cars before ever reaching the other side. A two-lane highway can separate a population of salamanders into two, essentially isolated populations.

Structures such as tunnels, underpasses, and drift fences can be used to retrofit existing roads for herp traffic.

  • In Massachusetts, two tunnels were built to help salamanders move from their vernal pools to the spring where they mate and lay their eggs. Previously, locals used a bucket brigade method of helping the salamanders cross.
  • Along U.S. 441 in Florida, a 3 ½ foot wall was built with culverts underneath for the benefit of herps. The wall was built with a lip in order to deter animals from going over. Beneath the wall, they are directed to the culvert for safe passage underneath the highway.
  • Storm drain culverts were placed along State Highway 58 in San Bernardino County, California for the benefit of desert tortoises. In 1995 and 1996 five turtles where recorded using the passages on 75 occasions.

Written by John Housein

Recommendations

  • Avoid unnecessary road building through natural areas.
  • Reduce speed limits and display road signs to alert motorists through areas of high potential herp crossing.
  • Install underpasses and herp walls under roads that cross high herp traffic areas, such as between wetlands.