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In Yellowstone, It's a Carnivore Competition

Source:  Copyright 2003, Washington Post
Date:  May 19, 2003
Byline:  Guy Gugliotta, Washington Post Staff Writer
Original URL: Status DEAD


It was not a fair fight. The wolverine may have been as nasty as any predator in the mountains, but it weighed only 27 pounds. The black bear had arisen from a long winter's sleep and was almost certainly very hungry. The slain elk, carrying as much as 550 pounds of meat, was a prize worth fighting for.

"We don't know how it unfolded, except that the wolverine lost," said wolverine expert Kristine Inman, of the Wildlife Conservation Society. There were a few elk hairs on the ground and signs the bear had carried the elk away. The wolverine carcass was "intact," albeit with a crushed head and bear bites all over its body.

This encounter occurred April 22, an unusual example of predator killing predator in the remote reaches of greater Yellowstone Park, a 40,600-square-mile tract of wilderness spreading like an ink blot across the junction of Wyoming, Montana and Idaho.

But while the wolverine may have chosen a mismatch bordering on madness, scientists say that predators killing one another is probably part of the natural order of things, and greater Yellowstone is offering an unprecedented opportunity to test the theory.

With the reintroduction of the gray wolf in 1995, the park and its suburbs now have a full complement of North America's great carnivores: wolves, grizzly bears, black bears, cougars, coyotes and wolverines. Nowhere else on the continent can boast such variety.

And all the species, with the exception of coyotes, are prospering, either protected under the Endangered Species Act or by hunting or trapping restrictions. The Northern Rockies coyote population, which had the run of the park after wolves were exterminated in the 1930s, has been halved to 225 animals since the wolves returned.

"Things are starting to sort themselves out," said coyote specialist Robert Crabtree, of the Yellowstone Ecological Research Center. "When there are wolves and coyotes, there are always going to be kills of coyotes."

And evidence is growing that other species are fighting and dying as well. When meat-eaters have plenty to eat -- and there are about 14,000 elk in greater Yellowstone, the densest population on the continent -- they spend considerable time pushing one another around like bullies on a playground.

"It's a toothy world out there," said the U.S. Geological Survey's Chuck Schwartz, leader of greater Yellowstone's Interagency Grizzly Bear Study Team. "It is probably very normal in a multi-predator, multi-prey system for predators to compete for a carcass. It's all about numbers and size."

The male grizzly, 7 feet tall and weighing close to 1,000 pounds, "is the king of beasts, but they're slow," said Douglas Smith, who leads the National Park Service's Yellowstone Wolf Project. Next in the pecking order, albeit with some disagreement, come the wolves, the only predators who work in a team, followed by black bears, cougars, coyotes and smaller carnivores such as the wolverine.

The bears and the wolves can comfortably bring down an adult male elk. The cougar is a solitary hunter and prefers elk calves, but it can kill adults as well. Coyotes and smaller animals either have to scavenge other animals' elk kills or settle for mouthful-sized voles, squirrels, mice and other rodents.

An elk is a temptation that wolverines, and especially coyotes, can't resist: "If you can survive long enough to cash in on a big food source like an elk, you can eat well, produce pups and pass on your genes," Crabtree said. "But you have to avoid the wolves. If you don't, you die."

In the wolverine's case, the competitor was a black bear. Inman said it was not clear whether the bear or the wolverine killed the elk -- wolverines have been known to pull it off -- or whether the elk had simply thawed out after freezing to death or dying of starvation during the winter. However it happened, the pecking order prevailed.

No matter which carnivore kills the elk, researchers agree that greater Yellowstone is a ruthless place where losers often pay the ultimate price. Last month, 14 wolves caught a female cougar out in the open skulking around one of their kills. The wolves killed the cougar, then found her kittens and killed them. The dead female had wolf hair in her teeth and claws.

"The wolves will wade into a situation and check it out, and if it goes well, they'll keep going," Smith said. Sometimes it works, but sometimes it does not. Smith saw a male grizzly drive a pack of wolves away from an elk carcass, then make a "king of the hill" defense as the wolves darted in and out, trying, but failing, to wear him out.

But wolves do not always win. Males, at 125 pounds, can go after a 110-pound female cougar if they are in a pack, but a lone wolf is a bagatelle for a 160-pound male cougar. Smith has recorded two instances of cougars ambushing and killing single wolves -- one an adult, the other a pup.

"A lion has two sets of lethal weapons -- teeth and claws, whereas wolves' principal weapon is just teeth," said National Park Service cougar specialist Kerry Murphy. Cougars can dominate as long as they stay in the rocks or in the forest, where they can climb a tree. "We're still talking about dogs and cats," he said.

The wolves have had remarkable success since their return to Yellowstone, growing from an initial infusion of 37 animals to 273 today, in 31 separate packs. Still, Smith acknowledges, a female grizzly "is the single most dangerous animal in the mountains."

This is because bears, like some of the other predators, have more to fear from their own kind than they do from neighbors. Male bears will kill and eat a female's newborn cubs, perhaps to accelerate the female's breeding cycle. Male cougars will also kill a female's cubs and will take on another male if it tries to usurp its breeding rights.

Among wolves, killing one another is "part of the natural order of things," Smith said. "Wolves are ferociously territorial," he added, and are constantly fighting turf wars. Since the wolves returned to greater Yellowstone, there have been at least 30 pack conflicts, with 15 wolves killed, he said.

Crabtree suggested that these battles are one reason wolves sometimes let coyotes approach their kills, then chase them down, even though they represent no danger: "Maybe you want to teach your pups tricks of the trade," he said. "Maybe wolves are killing coyotes to practice for conflicts with other wolves later in life."

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