Inside the experimental world of animal infrastructures

But Banff Wildlife Crossings, like most, suffer from a kind of horseless chariot syndrome, their projects circumscribed by existing infrastructure. Tunnels are often poorly adapted culverts, the pipes (usually concrete) that ferry water under the roads. And overpasses have generally been borrowed in bulk from the streets: they’re built as if they would support the weight of an 18-wheeled vehicle and then “maxed out” in foliage, says Lister.


A handful of experiments are starting to rethink this model. One is the Wallis Annenberg Wildlife Crossing, the $ 90 million wildlife bridge under construction north of Los Angeles. Designed by architect Robert Rock, it avoids the humped arch of older bridges in favor of a vast flat expanse that needs a single column to support it between the mountains and across a highway traversed by some 300,000 cars every day. It’s the “cornerstone of innovation,” says Renee Callahan, executive director of ARC Solutions, a group that researches how to build better bridges for wildlife. “It’s literally designed for species, from mountain lions to mule deer to deer mice,” says Callahan. “They are designing it all the way, literally down to the mycorrhizal layer, in terms of soil, to make sure the soil itself has the fungal web that can support native vegetation.”

There are many unknowns at the start of construction, not least how the different species will react to the huge volume of vehicles passing underneath. The National Park Service will monitor activity on the bridge and DNA profiles of animals on both sides of the highway. Many are watching to see what will happen with the area’s mountain lion population. Over time, inbreeding has led to genetic abnormalities, such as a telltale knot in the tail of local cats. The agency predicted that the population would become extinct within decades without a crossbreed.

In the United States, the $ 350 million infrastructure bill is far less than what will be needed to address the fragmentation created by the country’s 4 million miles of public roads. But there are a handful of innovations that could overturn the cost-benefit analysis by allowing crossings to be built at lower cost or in places where it wasn’t previously feasible.

Animal bridges are currently only built where there is protected land on both sides of the road, as the typical expense of building a concrete bridge would be difficult to justify on a site that someone could develop within a few years. . Lighter, cheaper and modular modular systems could be used in places whose future is less secure, explains Huijser: “If the adjacent land becomes unsuitable for wildlife, we take it apart and you can move it.”

A candidate material for such modular systems is precast concrete. There is also enthusiasm for fiber-reinforced polymer (FRP), a less dense material than concrete that is made up of structural fibers fixed in the resin. FRP was used to build pedestrian and cycle bridges in Europe and a quick and easy wildlife bridge in Rhenen, just south of Gooi in the Netherlands. Currently the Federal Highway Administration does not allow its use in traffic infrastructure in the United States, but there are growing demands for change. “These are barriers that mainly concern politics and governance. They are not about science and they are not about technology, “Lister says.

“They know the last thing everyone wants is for a big structure to be built, with a lot of publicity, and then it doesn’t work.”

Darryl Jones

Designers like Lister and innovators like Callahan are strong advocates of building bridges for wildlife across the country. Road ecologists and wildlife scientists, on the other hand, remain more cautious. “They are hypercritical because they know that the last thing everyone wants is for a big structure to be built, with a lot of publicity, and then it doesn’t work. Because everyone will come out of the carpentry and say, ‘Look! Waste of time! A complete shit! ‘”Says Jones.

But today even the prudent types want to see more built. While we may not have conducted enough research to have all the answers, it would be dangerous to take that as a sign that we should stop, says Huijser. He calls this excess of caution a “type II error” – a false negative. In this period of mass extinction, it’s like the house is on fire and our solution so far has been to spray a water gun on it a couple of 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 as you build. We still have to invest in the real work of labeling, trail cam setup, DNA testing, and long-term population monitoring, she points out. But we have to build more crossings first, and the evidence we have so far says we build big and bold. “You have to realize that you almost can’t do too much,” she says. “Do what you think is necessary, study it and then, nine times out of 10, you’ll see, ‘Oh, I should have done more.’ But there is no point in waiting until you understand. “

Matthew Ponsford is a London-based freelance journalist.

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