When the U.S. tried to rid its cities and rural towns of coyotes starting around the 19th century, the effort backfired. While coyote control programs — involving chemical poisons, steel traps and paid bounties — did in fact kill tens of millions of the species, the population only spread further out. 

“They responded by taking over the entire continent,” says Peter Alagona, an environmental historian at the University of California at Santa Barbara. Coyotes can now be found in every state except Alaska, as well as in parts of Canada and Central America, and they’ve moved from the fringes of cities to urban backyards. 

“You have to admire their grit and adaptability for being able to live in Arctic tundra, in tropical rainforest, in deserts and in places like, you know, the Bronx,” he says. 

The resiliency of coyotes is recounted in Alagona’s new book, The Accidental Ecosystem, which retraces the land use decisions that have, intentionally or not, allowed some wildlife species to proliferate across the the U.S. even after they’d been deliberately targeted to make way for cities. It’s not just coyotes and commonly sighted critters like squirrels black bears, foxes and even pumas have been spotted wandering the streets of crowded metro areas. 

Bloomberg CityLab spoke with Alagona about the ways in which animals have adapted to cities and even thrived there, while urbanites struggled to coexist with them. The interview has been lightly edited for length and clarity.

Can you help us set up the series of events that led to the so-called “accidental ecosystem” in American cities?

There’s this early phase in which cities get established disproportionately in areas that were really rich and productive biologically, and where prosperous indigenous communities sprouted up. Wildlife gets cleared off the landscape and replaced in many of these growing urban centers with huge numbers of domesticated animals — livestock and animals we often think of today as pets — that were kind of filling the niches that wild animals would have filled. 

These domesticated animals then get cleared out by the late 19th and early 20th centuries, leading to this period from about 1920 to 1950 where there are fewer wild animals living in urban areas, particularly in North America, than really at any time before or since. This is a period in which some of the greatest thinkers about urban life were doing their writing, and almost everybody assumed that cities weren’t going to have animals in them.

But that gap in time is fascinating because cities, by planting trees, establishing new parks and cleaning up polluted areas — decisions that people made consciously for reasons that had to do with human health, human well-being, the urban environment, real estate values, those sorts of things — were setting the stage for wildlife to come back. The increasing leafiness meant that some creatures that depended on a tree canopy, like Eastern gray squirrels or the many birds that passed through, could return.