Road kill: A Risk to Wildlife Populations

Blue-spotted salamanders are at risk of local extirpation from road mortality when they travel to breeding ponds in the spring.

Collisions between wildlife and vehicles are one of the environmental consequences of roads. While it is only one aspect of road ecology, road kill is certainly one of the most visible. We all have observed dead deer, raccoons, skunks, or armadillos on the road. While it is certainly unfortunate for these individual animals, their population or species is generally not at risk. Our concerns are usually limited to public safety and damages to vehicles. However, we hardly notice the countless small birds, small mammals, reptiles, and amphibians we hit or run over frequently. Here’s what we know about the conservation significance of road kill for wildlife:

Songbirds are being killed by cars at high rates. This is in addition to the hundreds of millions of birds killed every single year by communication towers, wind towers, house cats, and windows. This accumulation of stresses on bird populations may be enough to threaten some species over the long run.

Some amphibians that breed in ponds and wetlands, such as spotted salamanders and wood frogs, migrate in large numbers during a couple of wet spring nights. On their way to their breeding ponds, they may cross roads in large numbers. When these crossings occur over busy roads, it can lead to massive mortality events. Eventually, some species can be locally extinct mainly because of these massive road mortality events.

Because of how slow they are, turtles are vulnerable to cars. They often need to cross roads to move between wetlands, or to access nesting areas. In addition, the soft roadside dirt often attracts turtles looking for a sunny nesting spot. However, one of the biggest problems for turtle populations is the vulnerability associated with their population structure. Turtles are slow growing animals that start reproducing late in life, and produce few offspring every year. To balance this low productivity, they evolved a solid shell to ensure they can live a long time (some over 100 years) and have many chances at reproducing. That shell is no match to a car’s wheels, though, and adults that should enjoy a high survival are killed in their prime, leading to widespread population declines.

Road mortality may be a concern even for insects these numbers are particularly troublesome in light of the recent steep decline in monarch populations range-wide.

Mammals that have small population are sometimes directly threatened by extinction from road mortality. The Florida panther, with less than 200 individuals remaining, has been losing up to a dozen individuals a year because of road kill. Such a small population cannot sustain that level of pressure.

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