DENVER, May 8 (UPI) -- As the population of gray wolves expands across the northern United States, researchers are finding a surprising side-effect: Their presence appears to lead to a reduction in the coyote population.
Wildlife researchers at the University of Washington are using radio transmitter collars and game cameras to determine how the new presence of top-of-the-food-chain predators is influencing scavengers, or "kleptoparasites," particularly coyotes.
"Wolves really seem to have it in for coyotes," said Laura Prugh, associate professor of wildlife and forest sciences at the university.
In a "fatal attraction" scenario, coyotes that sneak up to the carcass of a wolf-killed elk or moose are attacked by their canid cousin in brutal ways, Prugh said.
"We've seen cases where wolves decapitated coyotes and buried their heads, kinda mob-style. It really is dog-eat-dog," she said.
Coyotes have expanded their territory nationwide into both human and wildland areas since the early 20th century, showing up in New York City's Central Park and on the streets of Los Angeles and Chicago.
In urban areas, they sometimes attack small pets and occasionally bite humans. They are hated by federal and state game officials, but trapping, poisoning and blowing them up with cyanide bombs does little to diminish their population.
"Coyotes are one of the most adaptable species on the planet," Prugh said. "They can coexist and persist with wolves and people."
Listed as endangered in 1974, gray wolves have rebounded in the northern Midwest states of Wisconsin, Minnesota and Michigan's Upper Peninsula. The species also has recovered in Montana, Idaho and the northern Pacific Northwest.
As movements grow to reintroduce wolves in western states like Colorado, coyote populations in wildland areas might drop, Prugh said. But she doubts wolves would follow coyotes into urban areas.
"Wolves don't do well with people," Prugh said. "Coyotes will always have a refuge in cities and places where there are lots of people."
Unlike wolves, coyotes hunt in pairs, or with a small pack of family members.
"They are extremely pair-bonded," said Prugh, who has witnessed coyotes snuggling in the wild. "But if their mate is killed, they'll find another mate within a month."
Coyotes can reproduce fast enough to compensate for up to 50 percent of their population being killed, Prugh said.
Coyotes usurped the ecological niche of top-level predators as wolves were killed off across the United States in the 1940s, said Roland Kays, a research associate professor at the Raleigh-based North Carolina State University and the North Carolina Museum of Natural Sciences.
"The wolves weren't there to keep them in their place," said Kays, who is not affiliated with the Washington research.
As mid-sized predators, coyotes don't go after elk, moose and even bison, as wolves can. "They sometimes kill a deer on their own, but they're not very good at it," Kays said.
Coyotes eat rodents, rabbits and even berries and insects, and in urban areas, outdoor pet food and garbage.
With the reintroduction of gray wolves in the northern United States, coyotes are getting an extra food source from wolf-kills in their role as scavengers, the Washington research shows.
"We often think, 'Oh the coyotes like to scavenge, it must be good for them,'" Kays said. "But this research turns an old idea on its head. It turns out that scavenging is an evolutionary trap, with more coyotes ending up dying from it as a result than benefiting from it."
Yellowstone National Park's coyote population dropped by 50 percent for the first five years after gray wolves became established, said Bob Crabtree, chief scientist at the Yellowstone Ecological Research Center.
A pack of wolves kill an elk, and eat as much as they can until they become "meat drunk," and leave the scene. That's when coyotes and other species try to scavenge the carcass, until the wolves come back, killing about 80 percent of the coyotes who got caught on the scene.
"You need to compete to eat -- and not get eaten -- in order to survive and reproduce," Crabtree said.
Coyotes, though less populous now in Yellowstone, got smarter as they became accustomed to wolves, he said.
"The coyote is an incredible survivor," Crabtree said. Coyotes are a native species that date back to the prehistoric Ice Age era, he said.
"In the La Brea Tar Pits, of the six most common species of prehistoric animal found, five are extinct, and coyotes are still here," Crabtree said.
For centuries, coyotes seemed to prefer open plains to forested areas, but research with game cameras shows the species has now expanded to U.S. forests, finding new sources of food, North Carolina's Kays' research shows.
For example, invasive coyotes have eaten their way through the population of Olympic marmots, large wood chucks that live in the high mountain forests of Washington's Olympic National Park, studies show.
"We'll see what happens if wolves make it to that area," Kays said. "Maybe the marmots will have a chance if the wolves kill the coyotes and things will be more in balance."