Over the past 100 years, coyotes have taken over America:
They are native to the continent, and for most of their existence these rangy, yellow-eyed canids were largely restricted to the Great Plains and western deserts where they evolved. But after wolves and cougars were exterminated from most of the United States by the 1800s, coyotes took their place. Colonizing some areas at a rate of 720 square miles per year, coyotes now occupy — or “saturate,” as one scientist I spoke with described it — nearly the entire continent. (Long Island is a notable exception.) The animals are now the apex predators of the east. And they’re proving so resourceful that even the last stronghold — the urban core — represents an opportunity to flourish.
Coyotes may be the most driven carnivores to penetrate modern cities in recent years, but they’re hardly the only ones. Raccoons, foxes, and skunks have long been prolific urban residents. And now bobcats, cougars, even grizzly bears — predators that symbolize wilderness, who typically require a lot of space and a stable prey base, and defend their territories — are not just visiting but occupying areas that scientists used to consider impossible for their survival. Dozens of grizzlies now summer within the city limits of Anchorage. The most urban cougar ever, a male named P22, has been canvassing Los Angeles’ Griffith Park for more than two and a half years. Bobcats prowl the Hollywood Hills and saunter near skyscrapers in Dallas. And in New York City, a predator is returning that hasn’t been seen since Henry Hudson’s day — the fisher, a dachshund-sized member of the weasel family with a long, thick tail. This spring, a police officer named Lenart snapped the first NYC photo of one, skulking on a Bronx sidewalk at dawn.
Why are these large weasels flourishing in the east?
“We found support that eastern fishers are experiencing what’s known as mesopredator release,” says Kays. “That means they overlap with fewer predatory species than they used to. There are no cougars; there are no wolves.” Without many big competitors to fear, middle-sized predators, or mesopredators, are free to change their habits: they can hunt in a wider range of places or times. They can also pursue larger prey (for fishers, that means hefty snowshoe hares, porcupines, or deer roadkill) without getting beaten to it or bullied. Scientists suspect that mesopredator release is fueling coyotes’ incredible expansion as well.
Most intriguingly, LaPoint and Kays discovered that the bodies of eastern fishers are actually getting bigger over time. These carnivores seem to be evolving to better catch larger-bodied prey by becoming larger themselves. A big, well nourished fisher is more likely to survive in new, challenging environments. “They’re getting bigger where their populations are expanding,” says LaPoint, which the team documented by comparing hundreds of museum specimens collected from the 19th century to the present. That’s brisk, evolutionarily speaking. “Within a century, more or less,” he says. “It’s pretty crazy.”
The rub is that this “wilderness” species seems to be quickly adapting to our presence. In persecuting North America’s biggest carnivores, we may be encouraging medium-sized ones to spread directly into the areas we now live, and in some cases, actually evolve into bigger, more resourceful predators.
(Hat tip to T. Greer.)