In perhaps the most literal use of social media ever, a Paris-based air quality monitoring company called Plume Labs (layers upon layers here) has teamed up with Twitter’s UK division to equip a flock of pigeons with tiny backpacks carrying air monitoring equipment. Those birds (or, okay, their internet-connected backpacks) spent last week providing local pollution readings to Londoners who tweeted to them at @pigeonair.

They’re called the Pigeon Air Patrol, and there are ten of them. The idea was cooked up by marketing company DigitasLBi, and was the 1st-place idea in the 2015 Powered by Tweets exhibit and competition at the London Design Festival.

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It’s an interesting example of putting Twitter’s [fortunate-stock symbol=”TWTR”] interactivity and liveness to use, and seems to have sparked a lot of conversation about pollution in London. While the U.K.’s capital might not hold a candle to deadly locales like Beijing or Mumbai, London does have serious air quality problems, thanks to auto emissions, residential emissions, and dust from the Sahara Desert.

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The Pigeon Air Patrol is part of the larger Air Patrol project, which is calling on humans to wear Plume’s personal air pollution trackers as part of a crowd-sourced map of pollution patterns in London.

According to the projects’ organizers, the backpacks are “light as a feather,” and so far, it doesn’t seem PETA is ruffled.