Effect of a motorway on mortality and isolation of wildlife populations

Although motorways could affect wildlife species, only few studies have bee n documented on their effects on mortality and isolation. With 2266 road-ki lled animals representing 97 species, the results of a study on a motorway section emphasized that traffic considerably affected vertebrate population s (14.5 animals day(-1) 100 km(-1)). Road-killed animals were mainly mammal s (43.2%), with predators also suffering critical impacts (21.7% vertebrate s). Rare or endangered species such as the Midwife toad, the Blue throat, t he little Horseshoe bat, or the European otter were among the victims. Anim al mortality exponentially increased with traffic volume. Mortality reached almost 100% of migrants when no passage existed, and this barrier effect w as only reduced when underground passages crossed the road restraining the mortality to 31% of migrants in Field mice and 23% in Common toads, while m ortality always exceeded 74% in a road section with fauna ducts. It is reas onable to conclude that traffic severely influenced both wildlife species d emography and population exchanges resulting in effective population isolat ion.