Roads As Migratory Barriers

A few days ago, the New York Times covered some of the issues surrounding roads and animal migration.

There are some four million miles of roads affecting 20 percent of the country, and in the last 10 years the new field of road ecology has emerged to study the many impacts of roads, and how to mitigate the damage....

One of the first projects in this country to ameliorate the effect of roads was on Florida’s Alligator Alley on I-75. A series of 24 underpasses restored water flow to the Everglades and allowed wildlife to safely migrate. The changes reduced the mortality of Florida panthers — of which there were only around 50 — from 4 per year to 1.5.

Now, the number of ecologically sensitive road designs built or under way in the country is in the hundreds. In Amherst, Mass., salamanders emerge from hibernation in the mud on the first rainy night of April. “They come up and go screaming across the street to their breeding pond and have an orgy,” Dr. Forman said.

So many were being killed that locals stopped traffic on the night they emerged to let them cross safely. In 1987 engineers placed a tunnel under the road, with two fences to funnel the amphibians to the crossing.

The gold standard for wildlife-friendly roads is in Banff National Park in the mountains of western Canada. The country’s major highway, Trans-Canada 1, passes through the park, and with 25,000 vehicles per day, wildlife vehicle collisions were very frequent.

There are 24 crossings (all but two underpasses) and they have reduced collisions with ungulates by 96 percent and all large mammals by 80 percent.

The U.S. government is trying to integrate migration mitigation into road design, but there are so many miles of roads that it will take a long time to solve all of the issues. Apparently one problem is that once populations of a species are separated by a barrier like a road, they are less likely to intermix if the barrier is removed. For endangered or threatened species, that leads to potential long term problems with genetic diversity. For more common species, the problems are more mundane, as with this sora.