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
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
Everything’s up-to-date in Kansas City
The streetcar system in Kansas City, Missouri, was once one of the most robust in the country. In 2016, 59 years after it ceased service, a new incarnation got on track, with smart technology playing a key role. The sleek new streetcars have notched more than five million free rides in their first two and a half years, and an extension to the 2.2-mile starter line is already in the works.
Digital kiosks along the line display local attractions, take visitors’ pictures, and measure air quality. Responsive traffic lights have reduced vehicle transit time along the route by an average of 36 seconds, which cuts down on greenhouse gas emissions by lowering the time cars idle at red lights. The city has also used data collected by sensors on streetlights to predict where potholes will form. Kansas City Chief Innovation Officer Bob Bennett says a successful smart city exists without most people noticing: “Things just work like they ought to work.” —Lisa Rodriguez
New way to keep city water clean
Some sea anemones extend their tentacles to catch a meal. At other times, they retract them. Researchers looking to simplify water treatment took this ability to change shape as inspiration for a new type of nanocoagulant. When added to water, the nanocoagulant exposes its core, which interacts with unwanted chemicals such as nitrate and other aquatic contaminants. Its shell causes particles to clump together and settle to the bottom. —Douglas Main
Copenhagen’s mountain of energy
With its flat landscape, Copenhagen is an unlikely ski destination. But a novel project called Copenhill aims to pair recreation with renewable energy. Copenhill is a massive facility on the city’s industrial waterfront that converts trash to electricity, providing power for 30,000 homes and heat for more than twice that number. Its sloping, 1,247-foot-long roof looks like it was made for skiing—because it is. The new structure will eventually include an urban ski park, a climbing wall, and a café with sweeping city views.
The plant is 25 percent more efficient than the previous waste-incineration facility and will capture its carbon dioxide emissions, in line with Denmark’s ambitious goal to become carbon-neutral by 2050. The idea of burning garbage has its critics, who say waste-to-energy plants merely reinforce wasteful consumerism. But in 2018 Copenhill processed almost 500,000 tons of garbage. That’s better than filling up landfills, which are potent sources of methane—a greenhouse gas that can ruin the prospect of anyone’s powder day. —Christina Nunez
Drones for urban tasks
The number of commercial drones may quadruple in U.S. skies by 2022. In cities, the uncrewed aircraft may be used to manage urban habitat, lug freight, and inspect buildings—but data they collect could be vulnerable to hacking.
Researchers at Russia’s Samara State Technical University have created cups out of pureed fruits and vegetables. Shaped using a plasticizer, the all-natural dishware is durable enough to contain boiling water—and you can eat it (it tastes like the original produce). While the project was initially aimed at reducing food-packaging waste for astronauts, it would be a useful addition to city kitchens—or any place seeking to reduce landfills. —Becky Davis