Suzanne Stone, Defenders of Wildlife

Derek Goldman, Endangered Species Coalition
406-549-2848 ext. 2

Chris Colligan, Greater Yellowstone Coalition

News and Opinion


Wolf-wolf killings and disease mean crash for Yellowstone wolf population
by CHRIS MERRELL, Casper Star-Tribune

LANDER - Adult wolves in Yellowstone National Park have been killing each other more than usual this year and wolf pups have been dying at the same time, apparently of disease, a park biologist said Tuesday.

It's a "double-whammy" that is likely to mean a crash in the overall Yellowstone wolf population this year, he said.

And the behavior of the adult canines this summer and fall—the relatively high number of wolves killing other wolves—could help confirm a decades-old theory that had long been discounted by many biologists.

Doug Smith, the wolf project leader for Yellowstone National Park, said there were 10 breeding pairs of wolves with surviving pups in the park last year, but this year he expects that number will be cut in half.

"It looks like we're having another disease year, but it hasn't been proven yet," Smith said. "So that's one half of the story. The other half of the story is we've had probably record-high wolf-wolf killing. We had two this last weekend, five in late August and early September. We've had a lot of wolves killing other wolves."

There have been two previous confirmed disease years for wolves in Yellowstone, one in 2005 and the other in 1999, Smith said. In both years, there was an outbreak of canine distemper in the population that killed many pups. Following the 2005 epidemic, the population in the park was down by 30 percent from the previous year's 169 wolves, he said.

"The disease typically affects the pups because adults, oftentimes, have immunity to these kinds of things," Smith said.

This year appears to be similar to 2005 and 1999, but he won't be sure until this winter, Smith said, when park biologists capture wolves and test their blood for antibodies.

Whatever has been killing the pups, it happened to hit when the population was reaching what Smith calls its "social maximum" of about 170 wolves in the park, which appears to be the point when the animals start killing each other, in earnest, to bring their numbers back down.

Since the re-introduction of wolves into Yellowstone almost 15 years ago, the park has never had a wolf population exceed 175 members, Smith said, and it appears that the wolves self-regulate their numbers to stay below the 170s.

Surprisingly, he said, this self-regulation seems to have less to do with food availability and more to do with how crowded the animals become.

This idea of a self-regulated wolf population for social reasons, rather than food availability, was first posited by a scientist in the 1960s, but it has since been rejected by most biologists, Smith said.

But now it appears the 40-year-old theory might actually be correct, because "wolf territory size can only be compressed so much before they start killing each other," he said.

This could mean wolves that are more spread out have populations determined primarily by the amount of prey available to the animals, but when the canines are densely populated, as they are in Yellowstone, their numbers are regulated more by territoriality even if there's plenty of food to go around.

Last year there were 171 wolves in Yellowstone, and although he wouldn't predict a specific number for this year, Smith said he expects the year-end total to be "way below that."

Mike Jimenez, the federal project leader for wolf recovery in Wyoming who was also the head of the state wolf management team when the animals were briefly delisted this spring and summer, was unavailable for comment Monday and Tuesday.

Eric Keszler, spokesman for the Wyoming Game and Fish Department, said he has not yet received any reports that Wyoming wolves outside of Yellowstone have also experienced a disease year.

Ed Bangs, the federal gray wolf recovery coordinator, said it's possible that the disease is killing pups outside the park, but officials don't know yet.

"There are a few less breeding pairs in Wyoming from our midyear estimate compared to last year, and that could be pup loss," Bangs said. "But we really don't get a good pup count until the winter."

This story first appeared in the Billings Gazette on October 29, 2008.

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