As biologist Jennifer Sheldon knelt over the coyote's body, it took only a moment for her figure out what had happened.
The signs were clear: The animal had been killed by a pack of gray wolves - another example that here in Yellowstone National Park it has literally become a dog-eat-dog world.
Ever since 14 Canadian wolves were transplanted into this venerated American nature preserve two winters ago, a ruthless turf war has ensued between the newcomers and their smaller but prolific coyote cousins.
It is a battle among predators being played out in the park's Northern Range, a landscape considered as biologically fecund as East Africa's Serengeti Plain. No one knows how it will end. But the rapid ascendance of wolves here on Yellowstone's snowscape - home to the greatest concentration of large mammals on the continent - is giving scientists pause. It's also providing fresh insights into the complexities of reintroducing large carnivores into a dynamic ecosystem.
"We knew there would be conflict between wolves and coyotes, but the degree of violence we've witnessed has been startling," says Robert Crabtree, a coyote expert documenting the phenomenon with Ms. Sheldon, who is also his wife. "I guess you could say this is nature's version of mano a mano."
Yellowstone's lead wolf biologist, Doug Smith, says the interspecies battle for superiority, in addition to the broader impact that wolves are having on the ecosystem as a whole, is helping scientists better understand the reintroduction of native species, a controversial but growing practice in the United States.
Ironically, coyotes are being purged from the niche they inherited 70 years ago when bounty hunters exterminated wolves from the park. However, it appears the coyote's loss may produce big dividends for other animals.
In the wolf's absence, coyote numbers swelled to unnatural levels, resulting in depressed numbers of pronghorn, beaver, and ground squirrels, says Mr. Crabtree, who is now halfway through an unprecedented 15-year study of 500 coyotes. The drop has meant less available prey for other predators and the loss of beaver-created wetlands, which are important to moose and songbirds.
Yet, like a rock falling on the calm surface of a pond, wolves have caused biological ripples in all directions.
"What's impressive to me is how this reveals the complexity of these systems and how one species, be it a coyote or a wolf, can trigger off a whole stack of dominoes," says Hank Fischer, the northern Rockies field representative for Defenders of Wildlife. "We're just beginning to get a glimmer of what's in store."
The biological diversity in the park's Northern Range - packed with bison, elk, bighorn sheep, mountain lions, grizzlies, and now wolves - makes this an exceptional laboratory. "Where else do you have the full original complement of predators that existed prior to the arrival of Columbus?" Crabtree asks. "What makes Yellowstone so much like the Serengeti is that for a researcher it is open and accessible. You can see the interactions play out right before your eyes."
Wolf packs have attacked coyotes, killed their young, invaded their dens, and made the shaggy wild dogs, which were commonly sighted by tourists only five years ago, a rarity.
"Wolves have really reshaped the presence of coyotes in Yellowstone, not just in reducing their numbers but forcing them to the perimeters of their home ranges," adds John Varley, director of the Yellowstone Center for Research. "They way they've done it hasn't been pretty."
Yellowstone officials attribute an increasing number of attacks on coyotes to the fact that wolf packs are colonizing wider areas of the park and solidifying the perimeters of their territories. And Sheldon, whose field work is being supported by a grant from Defenders of Wildlife, notes that the number of coyotes in the Lamar Valley has dropped 50 percent. That includes a 30 percent reduction in the number of coyote packs and a 33 percent reduction in average pack size.
"Often nature's changes are so gradual as to be undetectable in a human lifetime," Sheldon says. "What has been so compelling about wolf restoration is to see the immediate and profound responses which have occurred in just 2-1/2 years."
Prior to 1995, few North American researchers could boast of having observed the deadly interaction between coyotes and wolves firsthand. But during the past 18 months, Sheldon, Crabtree, and a team of assistants have documented 30 instances where wolves have swarmed coyotes, and a third of those encounters have resulted in coyote deaths. They know it represents only a fraction of the toll.
The drama in Yellowstone has attracted national attention because it hints at what may lie ahead for other ecosystems. Every other region where wolf reintroduction is currently proposed - the Adirondacks of New York, the Olympic Peninsula of Washington, southern Colorado, and New Mexico - also has healthy coyote and big-game populations.
And while wolves are yielding obvious benefits for Yellowstone, ranchers still grumble about what will happen when more wolves move outside Yellowstone. Over the past three years, Defenders of Wildlife has compensated nine ranchers about $12,700 for 86 sheep and five calves.
Still, the livestock losses are below what was predicted in an environmental review that cleared the way for the wolves' return, although Fischer admits that 1997 has seen the largest percentage of wolf-killed livestock.
Meanwhile, the Yellowstone wolf population continues to grow. Today, augmented by the shipment of another 17 Canadian wolves in 1995, it has grown to 86 free-ranging animals, including 46 pups born last spring and summer.
With the government's goal for wolf recovery here set at 10 packs numbering 10 animals each, there is already talk of removing this population from the list of federally protected species.
"Nobody expected we would have this level of wolf reproduction this quickly," says Fischer. "We are very close to achieving recovery goals, and with a good crop of pups, that could happen next year."