They too shall pass: Wildlife crossings now go the extra mile - Hindustan Times
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They too shall pass: Wildlife crossings now go the extra mile

ByAnesha George
Feb 23, 2024 05:19 PM IST

Canopy bridges for monkeys, ropeways for squirrels, ladders for fish. Wildlife crossings are finding new ways to ferry animals across highways and tunnels.

There’s an unusual problem plaguing the hilly English town of Warminster.

The Ecoduct De Borkeld in the Netherlands. (Adobe Stock) PREMIUM
The Ecoduct De Borkeld in the Netherlands. (Adobe Stock)

A road runs along the edge of a nature reserve here. And every year, in peak frog-breeding season (February-March), residents run over hundreds of frogs, toads and newts just trying to make it from the woods on one side to the ponds and marshes that are their breeding grounds in the reserve.

Toad Patrollers, teams of local volunteers, rescued over 1,200 of these creatures even between the non-peak breeding seasons of April and Octoberlast year, by popping them into buckets and carrying them across the road in batches. There are plans to now build fences, set bucket traps, and empty those out periodically. But residents fear the frogs could freeze to death in their buckets, if temperatures suddenly drop.

A final decision on whether to close the roads completely, during these months, will be taken on March 25. As local resident Harriet James, who manages the Toad Patrollers, pointed out to the BBC: “We can’t be there all night. We find there are certain nights where there are hundreds of them marching down to the pond.”

How to get animals safely from one side of a disruptive invasion to another — roads, flyovers, bridges, canals, tunnels, underpasses… the list is long — is an increasingly pressing issue as built infrastructure extends further into once-remote or once-protected zones.

Wildlife crossings are, as a result, becoming more innovative.

Fish ladders, squirrel ropeways, reindeer viaducts and a range of other overpasses and culverts are being deployed around the world.

In July, the Amazon in Brazil got its first aerial canopy bridge for woolly monkeys and black-headed spider monkeys. (Michael Dantas / WCS)
In July, the Amazon in Brazil got its first aerial canopy bridge for woolly monkeys and black-headed spider monkeys. (Michael Dantas / WCS)

In July, for instance, the Brazilian Amazon got its first aerial canopy bridge for arboreal animals, a project that was completed before the federal highway below it opened. It is essentially a ropeway at treetop level that allows large primates such as the at-risk woolly monkey and the endangered black-headed spider monkey, as well as opossums, squirrels, anteaters, kinkajous, snakes and lizards, to remain in their habitats as they make their way across what is now a bustling roadway at ground level.

In Sweden, authorities have announced plans to build several renoducts or reindeer viaducts across a major highway. These bridges will be covered in local vegetation, and will allow the reindeer to forage for lichen across a wider habitat, particularly when unseasonal rains (increasingly common amid the climate crisis) cover their usual pastures in icy sheets.

In the US, work has begun on the country’s largest urban wildlife crossing, the Wallis Annenberg project. This massive bridge — 200 ft long and 165 ft wide — will span the 10-lane 101 Freeway in southern California. Due to open in 2025, it will link critical mountain-lion habitats in the Santa Monica Mountains, Santa Susana Mountains, Simi Hills and Los Padres National Forest.

Mountain lions and cougars have been killed on the freeway, and have been spotted wandering along it, unable to cross. This, in fact, is what prompted the public-private project funded partly by donations.

“Today, wilderness is routinely interrupted by cement and tar roads as we race to connect the remotest areas,” says Anish Andheria, president of the NGO Wildlife Conservation Trust. “Conservation is about making room for growth, but keeping the ecological cost of it down as well.”

Andheria is a part of a committee consulting with the Maharashtra government on mitigation efforts around the new 701-km Samruddhi Expressway between Mumbai and Nagpur.

While several overpasses, underpasses and tunnels for leopards, nilgai, chinkaras and wild pigs have been built, an often-forgotten category in such cases, he says, is insects. Thousands of beetles, bees and butterflies fly into windshields, drawn by the light and heat of passing vehicles. Simple design changes can prevent this loss; plant non-flowering plants in dividers, for instance, and insects will have one less reason to fly into traffic.

The wildlife bridge along NH44 in India is used by about 18 species, including tigers. (Wildlife Institute of India)
The wildlife bridge along NH44 in India is used by about 18 species, including tigers. (Wildlife Institute of India)

India got its first major wildlife bridge in 2019: nine concrete pillared walkways, built beneath the NH 44, along the Kanha-Pench wildlife corridor. They are in use by 18 different species, according to a 2021 report by the Wildlife Institute of India. The Indian hare and jungle cat are the most frequent users, camera trap data showed, followed by spotted deer, gaur, nilgai, sambar, wild pigs, tigers, leopards, wild dogs, sloth bears, jackals and the rare rusty-spotted cat.

In all, 89 tiger crossings were observed across all nine walkways between March and December 2019, the report stated. “The landscape has some prime tiger habitats and the most genetically diverse tiger population in India. It is also one of the most fragmented due to human activities,” Akanksha Saxena, a researcher on the project, told HT when the report was released in 2020.

But it took public interest litigation to make this underpass happen, which is an adversarial approach rather than a proactive one, points out Uma Ramakrishnan, a molecular ecologist, professor and researcher at the National Centre for Biological Sciences (NCBS), Bengaluru. Wildlife connectivity should be a consideration before such infrastructure is approved and long before it is built, she adds.

Additionally, researchers have suggested that more shrubs be planted in the tunnel, and that the concrete pillars be painted in camouflage colours. A viaduct must look and feel like a natural progression or it will not find as many users. Elements such as native fruit trees can help draw certain species, such as elephants.

The world’s longest wildlife bridge is a good example of welcoming design. Opened in the Netherlands in 2006, the Sand Quarry Nature Bridge is 2,600 ft long and 160 ft wide; spans an arterial road, a railway line, and a sports park with golf course. To draw its users — which include deer, foxes, rabbits, pine martens, badgers and frogs — it also houses pools at intervals.

Swimming up the ladder

A fish ladder at Bonneville Dam, USA, ferries salmon. (Adobe Stock)
A fish ladder at Bonneville Dam, USA, ferries salmon. (Adobe Stock)

One would think that wildlife crossings for the aquatic world would be the trickiest. And yet “fish ladders” frequently help migrating marine species pass over or around an obstacle such as a small dam. Even more intriguing is that fact that these devices have been around since 1837.

The first known fishway was built and patented in Bathurst, Canada, by lumber mill owner Richard McFarlane. It was a series of small, stepped ponds with water flowing through them, that helped fish swim out of the river, over his mill dam, and back into the river again.

The most recent evolution is a “fish elevator” in Maine that helps migratory species such as the American shad and river herring get to the top of the Milford Dam, in the Penobscot river. Built in 2017, the simple mechanism consists of large tanks at the base of the dam that essentially gather up the migrating fish, then rise to the top of the obstruction like lifts, where they empty their contents — fish, water and all — into the reservoir, so that the fish can continue their journey upstream.

Data suggests that millions of herring and hundreds of shad have used these elevators.

Right of passage

Meanwhile, in the UK, data on how few bats were using seven exorbitant bat bridges built in 2017 have turned that effort into a punchline.

The problem began when trees and hedges were removed to make way for the 19.5-km Broadland Northway in Norwich. With nothing to ping their echolocation signals off, the fear was that the area’s numerous bats would begin to fly into traffic. So the seven pylon-and-netting bridges were built, as guides, at a cost of 1 million GBP.

A report released by the Norfolk County Council in 2018 registered a very low number of bats using the structure per survey. Light and sound pollution from the traffic, and the disrupted tree-canopy line, were cited as possible reasons.

“I’ve no idea who came up with this strange idea, nobody seems to admit to it now,” John Altringham, an ecologist at Leeds University, told The Independent about similar bridges built in 2015. “It seemed to me even before we did the science that no self-respecting bat was going to look at these strange things.”

Monitoring wildlife infrastructure after it is built is key, says Abhinav Tyagi, a researcher with NCBS who has been studying the effects of habitat fragmentation on animal genetic and population dynamics. “Installing trail cams, sustained DNA testing and population monitoring can help us learn how to build this infrastructure better.”

It is also important to remember that wildlife crossings are far from ideal; the dangers of invading intact habitats cannot be erased, conservationists point out. “Once we accept that, we can search for the right technology — to reduce disruptions from on-site construction, for instance,” Andheria says. “We need to be committed to looking in the right direction.”

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