Effects of Roads on Roadkill

An estimated 1 million vertebrates a day are killed on roads in the United States (Lalo 1987). However, these documented roadkill rates are significant in reducing populations of only a few rare species in North America, and these kills generally are on high-speed highways (Forman and others 1997).

Studies show that the number of collisions between animals and vehicles is directly related to the position of the nearest resting and feeding sites (Carbaugh and others 1975). Because most forest roads are not designed for high-speed travel, relatively few large mammals are killed by vehicles on forest roads (Lyon and Marzluff 1985). Exceptions are forest carnivores, which are especially vulnerable to road mortality because they have large home ranges that often include road crossings (Baker and Knight 2000).

Forest roads pose a greater hazard to small, slowly moving, migratory animals, such as amphibians, which are highly vulnerable as they cross even narrow forest roads (Langton 1989). Nearly all species of reptiles use roads for cooling and heating, so many of them are killed by vehicles. Highways and other roads that support moderate- to high-speed traffic are population sinks for many species of reptiles, and result in reduced and increasingly isolated populations (Wisdom and others 2000). Predators and scavengers are killed while they feed on road-killed wildlife, as are other species attracted to roads because of salts or vegetation, or because roads facilitate winter travel (Baker and Knight 2000).

Despite the large body of data documenting annual roadkill, little research has focused on how to mitigate the effects on wildlife populations.

See also: Habitat Fragmentation and Predation