Unseen Passage: Roadkill

Around 194 millions birds and 29 million mammals are thought to be killed each year on European roads, according to a new study that has ranked the most vulnerable species. The research has found that the species killed most often were not necessarily the endangered species. This means action to preserve wildlife when new roads are built risks being targeted at the wrong species based on current methods. Road densities in Europe are among the world’s highest, with 50% of the continent within 1.5 km of a paved road or railway. Roads are therefore a significant threat to wildlife, and evidence shows deaths on them could even cause some species to disappear completely.

Despite this, the long-term protection of species is not currently considered when assessing the impact of new roads on wildlife, meaning we risk giving support to only the endangered species, doing nothing to help those most at risk. A better understanding of which species are most vulnerable to roads is therefore important if we are to take a more effective action of protection.

A research team based in Lisbon calculated road-kill rates for 423 bird species and 212 mammal species. They found that small animals with high population densities and which mature at an early age were most likely to be killed on roads. Nocturnal mammals and birds with a diet of plants and seeds were also shown to have higher death rates.

The study also used the road-kill surveys to rank the bird and mammal species whose long-term survival was most threatened by road-kill. The hazel grouse and ground squirrel were found to be the most at risk of local extinction. Both are common in Europe but are classified as species of Least Concern Red list of Threatened Species.

The most vulnerable animals classified as threatened by IUCN were the red-knobbed coot, Balcan mole and Podolian mole. The study revealed that road-kill hotspots were not the areas with the highest population of endangered species. For example, house sparrows had a high road-kill rate (2.7 per km/year) but were ranked 420th of 423 bird species for vulnerability. Conversely, the hazel grouse had a low predicted road kill-rate (0.2 per km/year) but was most vulnerable of all birds studied.

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