Wildlife Bridges Over Roads

Sweden’s announcement this week that it is to build a series of animal bridges is the latest in global efforts to help wildlife navigate busy roads.


Every April, Sweden’s main highway comes to a periodic standstill. Hundreds of reindeer overseen by indigenous Sami herders shuffle across the asphalt as they begin their journey west to the mountains after a winter gorging on the lichen near the city of Umeå. As Sweden’s main arterial road has become busier, the crossings have become increasingly fractious, so now Swedish authorities have decided to build up to a dozen “renoducts” (reindeer viaducts) to aid the crossings and allow reindeer herds to reach grazing more easily.


The renoducts are part of a growing number of wildlife bridges and underpasses around the world that aim to connect fractured habitats. On the Yucatán peninsula in Mexico, underpasses have been used to shield jaguars from traffic. Natural canopy bridges in the Peruvian Amazon have helped porcupines, monkeys and kinkajous pass over natural gas pipelines. On Christmas Island, bridges have been built over roads to allow millions of red crabs to pass from the forest to the beaches on their annual migration.


The wildlife bridges help avert some of the billions of animal deaths that happen on the roads every year around the world and counteract unintended consequences of human infrastructure.


In southern California, there have been signs of inbreeding among lions in the Santa Monica Mountains because busy freeways around Los Angeles have isolated populations with low genetic diversity. To help save the mountain lion population from local extinction, an $87m (£63m) wildlife bridge is planned over the 101 highway north of LA, which would be the largest in the world.

One of the most successful uses of wildlife bridges in the world is in Canada's Banff national park (pictured), where authorities installed seven overpasses and 41 underpasses on the section bisected by the Trans-Canada Highway. A 2014 study found that fencing off the road and installing wildlife passes had maintained high genetic diversity in black and grizzly bear populations. Furthermore, there was a big fall in roadkill along the highway, and a significant reduction in human mortality from animal collision, too.


In the UK, wildlife bridges are likely to form part of the government’s nature recovery network which aims to link together biodiverse areas under a 25-year environment plan. A 2015 review by Natural England acknowledged the benefits for nature and cited the example of the Netherlands, which is developing a network of “ecoducts” to help animals move around the country.


Highways England is increasingly building wildlife bridges as part of schemes around the country, with more planned for future infrastructure work.

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