It’s a bird! It’s a plane! It’s … a pigeon wearing a backpack? As part of an experiment that ran March 14 to 17, French startup Plume Labs outfitted 10 of the so-called rats of the sky with tiny sensors designed to offer a real-time snapshot of London’s ozone and nitrogen dioxide levels. But the ultimate goal, says Romain Lacombe, who worked on the project, is to get humans to wear similar devices that Imperial College London could mine for shareable insights–like which route people should walk if they want to breathe the best air. “It’s harder to get that from fixed monitoring stations, which is how we measure pollution right now,” he says.
–Olivia B. Waxman
This appears in the April 04, 2016 issue of TIME.