Inside the experimental world of animal infrastructure

But Banff’s wilderness crossings, like most, suffer from something like endless carriage syndrome, and their design is limited by existing infrastructure. Tunnels are often poorly adapted gutters, (usually concrete) pipes that carry water under roads. And the overpasses are usually taken in bulk from the roads – they are built as if they would carry the weight of an 18-wheeled car and then “dressed” in greenery, says Lister.


Scattered experiments are beginning to rethink this model. One is the Wallis Annenberg Wildlife Crossing, a $ 90 million wildlife bridge under construction north of Los Angeles. Designed by architect Robert Rock, it avoids the crooked arch of older bridges in favor of a vast flat expanse that needs only one column to support it between the mountains and across a highway crossed by about 300,000 cars every day. This is the “child on the innovation poster,” said Rene Callahan, CEO of ARC Solutions, a group that is researching how to build better bridges for wildlife. “It’s literally designed for species from mountain lions to mule deer to deer mice,” Callahan said. “They project it all the way down – literally next to the mycorrhizal layer, in relation to the soil, to make sure that the soil itself has a fungal network that can support local vegetation.”

There are many unknowns at the beginning of construction, not least how different types will react to the huge number of vehicles passing underneath. The National Park Service will monitor the activity on the bridge, as well as the DNA profiles of animals on both sides of the highway. Many are watching what will happen to the mountain lion population in the area. Over time, inbreeding has led to genetic abnormalities, such as treacherous curves in the tails of local cats. The agency predicts that the population will disappear within decades without crossing.

In the United States, $ 350 million in the infrastructure bill is far from what will be needed to tackle the fragmentation created by the country’s 4 million miles of public roads. But there are a few innovations that could guide cost-benefit analysis, allowing intersections to be built at a lower cost or in places where this was not possible before.

Currently, animal bridges are only built where there is sheltered land on both sides of the road, as the typical cost of building a concrete bridge would be difficult to justify in a place that one could develop in a few years. Lighter, cheaper, modular systems can be used in places whose future is less secure, Huyser explains: “If neighboring lands become unsuitable for wildlife, we dismantle them and you can move them.

One candidate material for such modular systems is precast concrete. There is also excitement for fiber-reinforced polymer (FRP), a material less dense than concrete, which is made of structural fibers placed in resin. FRP was used to build pedestrian and bicycle bridges in Europe and a quick and easy bridge for wildlife in Rennes, south of Gooi in the Netherlands. Currently, the Federal Road Administration does not allow its use in road infrastructure in the United States, but there are growing demands for change. “These are barriers that relate mainly to politics and governance. “They’re not for science and they’re not for technology,” Lister said.

“They know that the last thing someone wants is to build a big structure with a lot of publicity – and then it doesn’t work.”

Daryl Jones

Designers like Lister and innovators like Callahan are vocal supporters of building bridges to wildlife across the country. Road environmentalists and wildlife scientists, on the other hand, remain more cautious. “They are hypercritical because they know that the last thing someone wants is to build a big structure with a lot of publicity – and then it doesn’t work. Because everyone will come out of the windows and say: “Look! Waste of time! Complete nonsense! ”Says Jones.

But today, even cautious guys want to see more built. Although we may not have done enough research to have all the answers, it would be dangerous to take this as a signal that we need to stop, says Husser. He called such over-caution a “type II mistake” – a false denial. At this time of mass extinction, it was as if the house was on fire, and our decision so far has been to spray a water pistol on it several times. To conclude that water is not the answer would be a mistake.


Despite the challenges in Ede and elsewhere, says van der Grift, the answer is to learn while building. We still need to invest in the actual work of marking, installing surveillance cameras and performing DNA tests and long-term surveillance of the population, he stressed. But first we need to build more intersections – and the evidence we have so far says we need to build big and bold ones. “You have to realize that you can hardly do too much,” he says. “You do what you think is necessary, you study it, and then, nine out of 10 times, you’ll see, ‘Oh, I had to do more.’ But there’s no point in waiting until you know that.”

Matthew Ponsford is a freelance reporter based in London.

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