From a tiny railway bridge for dormice in the UK to elk, deer and bears benefitting from a slew of new animal crossings in Colorado, wildlife bridges are having a moment. As the human footprint on the planet continues to expand, a growing number of roads and railways include provisions for wildlife to pass through fragmented landscapes.

In January, we reported on Sweden’s plans to build a series of “renoducts” to help reindeer traverse the country’s main roads. The Swedish Transport Administration has since completed an ecoduct over the E6 in Skåne in southern Sweden, the third in the county. In southern California, work is due to begin on the largest wildlife bridge in the world in 2022, to connect isolated mountain lion populations north of Los Angeles that are becoming dangerously inbred. Joe Biden has earmarked $350m (£260m) of his $1.2tn infrastructure package for wildlife bridges to lessen the multibillion annual cost of collisions.

“Ten years ago, wildlife bridges were experimental. We didn’t know whether they would work or not. Now they’ve shown they get huge reductions in collisions. In some cases, 85% to 99% reductions,” says Rob Ament, a road ecology expert at Montana State University. “You can design them for many species. Even out in the plains, we’re getting moose crossings in North Dakota.”

Wildlife bridges are found on every continent: there is an elephant underpass near Mount Kenya; the Netherlands has a network of ecoducts that may help the country’s first wolf pack in more than 140 years gain a foothold across the densely populated country; suspended water pipes are helping Java’s endangered lorises; and a bison bridge may help the animals cross the Mississippi.

Here are five projects from around the world helping animals make their way:

Alligator Alley, Florida

The 129km (80-mile) stretch of road between Naples and Fort Lauderdale bisects the Everglades, an enormous wetland that is home to thousands of alligators, deer and the endangered Florida panther. It used to be notorious for high-speed collisions with wildlife until the road was upgraded to a four-lane motorway and crossings were installed. Today, dozens of underpasses and fencing help wildlife navigate the road. A camera trapping exercise found panthers, black bears, skunks, deer, bats, birds and even fish use the crossings, and hope is growing the state’s wildlife bridge network could be extended north to connect potential habitats for the Florida panther. “Fencing is critical along Alligator Alley. It is a 10ft-high chain link fence with three-strand barbed wire on top. That’s to keep the wildlife off the roadway and on the crossing,” says Brent Setchell, a design engineer at Florida Department of Transportation, who identifies potential crossing sites by monitoring road collisions with panthers and bears. “The fascinating thing is we just started monitoring the crossings four or five years ago. We found an abundance of wildlife.”

‘The tunnel of love’ on the Great Alpine Road, Australia

Stretching through the Victorian Alps in south-east Australia, the Great Alpine Road posed an existential threat to a colony of critically endangered mountain pygmy possums. Even though there are only about 150 of the marsupials on Mount Little Higginbotham, testing revealed genetic differences between sub-groups separated by the road, which are also threatened by fire, disappearing food sources and invasive species. Conservationists decided to build a “tunnel of love” between the isolated groups to improve mixing and strengthen their chances of survival. Over the last two summers, 30 possums have been identified using the tunnel of love, often in spring when they wake up from hibernation. The tiny marsupials can cross the nearly 15-metre tunnel in just 15 seconds – sometimes too fast for remote sensing cameras to capture them.

India’s tiger corridor

India’s first dedicated wildlife underpasses were a hard-fought victory for environmental campaigners. The nine crossings in the Pench tiger reserve were a court-ordered mitigation measure on the country’s longest road, the 4,112km National Highway 44, which runs down the middle of the country. Collisions with big cats still happen on the multi-lane motorway, but environmentalists say the underpasses have highlighted the need for more wildlife crossings on India’s road network. A 2019 camera trapping exercise found at least 18 species use the crossings, including tigers, wild dogs, sloth bears, civets and leopards. “According to our calculation, some 55,000km of roads pass through India’s forests and protected areas, many of them through wildlife corridors,” Milind Pariwakam, a road ecologist with Wildlife Conservation Trust Mumbai, told the Hindu. More infrastructure projects now have wildlife passes, including the 1,380km Delhi-Mumbai expressway currently under construction, which includes India’s first animal bridges.

Bhutan’s elephant crossing

Nearly 700 Asian elephants roam Bhutan’s forest on the eastern edge of the Himalayas. The small Buddhist country sandwiched between China and India is known for its dramatic landscapes and environmental leadership, as one of the few carbon negative countries in the world. On the 183km east-west motorway, Bhutan’s first elephant underpasses were constructed to help the threatened animals move through the landscape.Monitoring from 2015 to 2017 found that 70 groups of elephants were recorded near the passes, with three-quarters passing through the structures.

Sloth bridges in Costa Rica

Wildlife passes are not always bridges or underpasses. In Costa Rica, canopy bridges are used to help sloths, monkeys and other wildlife cross roads to combat collisions, dog attacks and electrocutions on power lines. The rope bridges, which cost about $200 (£150), are installed by the Sloth Conservation Foundation in areas where rainforest has been interrupted by human development on the country’s Caribbean coast. Crossing roads is often deadly for the slow-moving creatures and the canopy bridges also help combat inbreeding. “People look at them and think that they’re so poorly equipped to survive because you see them crossing roads and trying to move around and they look so awkward and useless,” Rebecca Cliffe, head of the Sloth Conservation Foundation, told Bloomberg earlier this year. “But if you put them in a well-connected rainforest, then they are masters of survival.”

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