Cities are often viewed as environmental wastelands, where only the hardiest of species can eke out an existence. But as scientists in the fledgling field of urban ecology have found, more and more native animals are now adjusting to life on the streets.

Take America's biggest metropolis. As recently as a few decades ago, New York City lacked white-tailed deer, coyotes and wild turkeys, all of which have now established footholds. Harbor seals, herons, peregrine falcons and ospreys have likewise returned in force, and red-tailed hawks have become much more common. Meanwhile the first beaver in more than two centuries turned up in 2007; river otters last year ended a similar exile.

What's happening in New York is by no means an anomaly. Experts say that the adaptation of wildlife to urban areas is ramping up worldwide, in part because cities are turning greener, thanks to pollution controls and an increased emphasis on open space.

In North America, the phenomenon is perhaps best exemplified by the coyote, which colonized cities roughly 15 to 20 years ago. A recent study of the Chicago area found that urban pups had survival rates five times higher than their rural counterparts. “Coyotes can absolutely exist in even the most heavily urbanized part of the city, without a problem,” says Stan Gehrt, a wildlife ecologist at Ohio State University. “They learn the traffic patterns, and they learn how stoplights work.”

Other studies have found animals from hawks to opossums reaping benefits from urban life. “We need to be careful about thinking of cities as places that don't really have interesting biodiversity,” says Seth Magle, director of the Urban Wildlife Institute at the Lincoln Park Zoo in Chicago. “Our urban areas are ecosystems, with just as many complex interactions as the Serengeti or the outback of Australia.”