Reintroduced Wolves Devastating Ecosystem

Newly arrived wolves have quickly toppled coyotes as the dominant predator in Yellowstone National Park, killing many of the smaller canines and leaving coyote packs in disarray.

“We expected to see some impacts on coyotes, but we didn’t expect to see this much impact, this soon,” said ecologist Bob Crabtree, who has studied Yellowstone coyotes in cooperation with the National Park Service for more than five years.

Coyotes and smaller scavengers, such as ravens, eagles, foxes and weasels, may be benefiting from the leftovers at wolf kills, but the coyotes often pay with their lives.

Teams from Yellowstone Ecosystem Studies, Crabtree’s Bozeman-based research operation, have documented 13 coyotes killed by wolves in Yellowstone this winter. They estimate the total may be three times that many.

All but one of the 13 documented coyote kills were near an elk that the wolves had killed.

Crabtree and biologist Jennifer Sheldon suggest in a research report that coyote numbers in the Lamar Valley of northern Yellowstone may have fallen as much as 25 percent.

“It’s fascinating to watch this struggle take place,” said John Varley, head of Yellowstone’s wildlife and resource management division.

Biologists estimate that one of the most-observed wolf packs is killing an elk or other prey animal every three or four days. If other packs are doing the same, the wolves will come close to tripling the number of elk carcasses appearing on Yellowstone’s northern range each year to more than 1,000.

Until wolves returned to Yellowstone under the federal wolf recovery plan early last year, coyotes were top dog, so to speak, in the hierarchy of the park’s northern range.

There were few obvious conflicts between the two species at first, but within months the Crystal Creek pack was seen excavating coyote dens within its territory and killing coyote pups.

In early winter, when both coyotes and wolves begin to pair up for the mating season, the tension intensified. Biologists began documenting wolves killing coyotes, most often when coyotes approached wolf kills in search of an easy meal. Biologists watched the wolves kill a coyote in five instances.

In most cases, single wolves initially chased coyotes, which in some cases turned to confront their pursuers. When more wolves arrived, they typically circled the coyote, pinned it down and killed it in about 15 minutes. Then the wolves returned to feeding on their original kill, but they never ate the coyotes.

Even away from kills, Yellowstone’s coyotes are off-balance. Three of 10 packs that resided in the Lamar Valley before wolves arrived have disintegrated, Crabtree said. The howling and scent-marking that normally coincide with mating season has been absent in most of the other coyote packs.