How pigeons landed in cities, and more breakthroughs

With skyscraper ledges to nest on and humans dropping food, pigeons flocked to New York City, home to more than a million of the birds.

This tiny pigeon is a New York City native—but his ancestors were not. According to the New York Public Library, Europeans brought pigeons to U.S. shores, probably in the 1600s, to raise as food or as a hobby. Some pigeons escaped and made their way to cities, where the ledges of tall buildings were as hospitable for nesting as the cliffs of their wild homes. Unlike bird species with specialized diets, pigeons can thrive on almost anything, including humans’ litter and leftovers. Small wonder that the world pigeon population is estimated at 400 million, with more than a million—and perhaps as many as seven million—of those in New York City. —Patricia Edmonds

(See why these pigeons wear elaborate sweaters.)

Twenty to 30 percent of the world’s urban water supply is lost to leaks each year. “In many cities, we don’t even know where the pipes are,” says You Wu of WatchTower Robotics. As an MIT student, Wu developed a squishy, shuttlecock-shaped robot that, when dropped into a water system, records the location of fractures. The next step? “A robot that can not only detect leaks but also repair them,” says Wu. —Kristin Romey

More from The Cities Issue

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This man spends 8 hours every day commuting. He's not alone.
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