A family of black bears cross a highway in Canada.
Credit: Liam Brennan
Canadian researchers measured wildlife overpasses around the world and found 71% in North America are narrower than recommended.
These bridges let bears and other creatures cross over busy highways, allowing animals to live and breed across their normal habitats—an important factor for biodiversity. Previous research has recommended a minimum width of 50 meters and a width-to-length ratio of 0.8 to ensure larger animals feel comfortable crossing.
Wider is better
Researchers used Google Earth to measure wildlife overpasses. They counted 120, with the majority narrower than local width guidelines. In North America, 20 out of 28 were narrower than 50 meters. Then they analyzed camera data from 12 North American overpasses and found wider overpasses had more animals of more species crossing per day than narrower ones.
"Overpasses are a win-win: they promote biodiversity and, with other measures like fencing, save animal and human lives," says Liam Brennan, a UBC undergraduate student. What's needed now, he says, is localized guidelines for overpass dimensions, and monitoring to ensure they're working for the animals they're designed for.
The research is published in the journal PeerJ.
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