Protecting Wild Animals Has Never Been More Urgent. But There’s a Reason It Can Be Harder Than It Seems.

Science Protecting Wild Animals Has Never Been More Urgent. But There’s a Reason It Can Be Harder Than It Seems. Ineffective “bat bridges” in the U.K. have something to teach us. By Helen Pearson April 28, 20265:45 AM Photo illustration by Slate. Photo by webclipmaker/iStock/Getty Images Plus and CreativeNature_nl/Getty Images Plus. Copy Link Share Share Comment Copy Link Share Share Comment This essay is adapted from Beyond Belief: How Evidence Shows What Really Works, by Helen Pearson. Copyright © 2026 by the author and reprinted with permission of Princeton University Press. Near the border of Norfolk in England, some weird-looking wire bridges span a busy road. They consist of pairs of poles on each side of the road, with a strip of wire mesh strung between and running down to the ground on either side. These are bat bridges, and they are a good example of a well-meaning conservation idea gone wrong. The bridges appeared in 2014, when an extension of the A11 road was being built. The new section cut a path through Thetford Forest, a vast and precious woodland which is home to several bat species. Major roads are bad news for bats: They can disrupt feeding, breeding, and flying routes. Many bat species fly close to the ground or trees and will avoid crossing a road. If they do cross, they’re likely to do so at traffic height and are often killed by vehicles. Bats are protected by law in the U.K.—some species are at risk of extinction—and so developers have to assess the environmental impacts of a new road on bats and take measures to mitigate them. The authorities behind the A11 extension decided to build a series of bridges to help bats cross the road. Bats navigate by emitting high-frequency sounds and detecting their echo, and the theory was that bats speeding toward the new road would detect and follow the line of the wire bridge upward and over the road, just as they follow the line of a hedge. Several mainland European countries had installed similar bridges and a handful already spanned British roads further north. In August 2014, part of the new A11 was closed for five nights so a suite of bat bridges could be installed at an eventual cost of more than half a million dollars. Was there any evidence that bat bridges would conserve bats? The best person to answer this question was John Altringham, an ecologist with a specialty in the creatures. Altringham started examining bat bridges in 2007, and was skeptical about them from the outset. While it was reasonable to think that a bat bridge could work like a substitute hedge, he could see that the bridge’s exposed high wires didn’t look like a hedge, didn’t sound like a hedge to a bat’s echolocation, and didn’t feel like a hedge because it was elevated and failed to offer the shelter of a low-lying hedge. If Altringham, a bat expert, had wanted to design something that might help bats cross the road, then a bat bridge would have none of the necessary properties. In fact, he could never understand where the idea had come from. Advertisement Advertisement Advertisement Advertisement In 2012, before the A11 bat bridges were built, Altringham and fellow ecologist Anna Berthinussen had tried to assess whether bat crossings in northern England were being used. They monitored the behavior of bats at foraging routes around the bridges and compared it with routes without a crossing. The scientists found no evidence that bats were more likely to cross the road using bridges or that they…

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