ANWR Bears Prey Upon Musk Oxen

KILLS: Grizzlies have learned how to take down ungulates.


By Doug O'Harra / Anchorage Daily News / September 29, 2003

 

I n what offers a harrowing glimpse into the unforgiving relationship between predator and prey in the Arctic, studies by federal and state biologists have documented a dramatic increase in musk ox kills by brown bears in the Arctic National Wildlife Refuge over the past decade.
Beginning in the 1980s when ANWR musk ox numbers peaked, a number of individual Arctic grizzlies learned how to stalk and take down the dangerous, shaggy ungulates with their sharp curving horns, said ANWR ecologist Patricia Reynolds, with the U.S. Fish and Wildlife Service.

"Some of them started to eat them, and some of them got good at it," Reynolds said in a phone interview last week. "I think the reason that bears are efficient predators is because they are adaptable, and they have the ability to switch to whatever is out there."

A few of these bears have taken their new skills to a higher level. In at least 10 instances, the bears killed two to seven musk oxen at once, possible examples of a relatively rare phenomenon biologists call "surplus killing," where a predator kills more prey than can be consumed immediately.

"This really surprised us," Reynolds told scientists at an Arctic science conference in Fairbanks last week, where she presented a paper called, in part, "A Search for Weapons of Muskox Destruction."

In an article published last year in the journal Ursus, Reynolds and two co-authors reported that 28 of 46 known musk ox deaths took place during multiple kills, with most occurring since 1999.

Bears don't usually engage in such surplus killing. What's especially intriguing is that musk oxen can be exceedingly dangerous prey, able to gore attacking bears with thrusts from their powerful heads and their sharp horns. At least one bear is thought to have died as a result of battling musk oxen on the tundra, and others have been wounded.

"It's a risk to them, and that's the interesting trade-off," Reynolds said. "Say a bear does get wounded or hooked. Will it try it again?

Though scientists have not observed one of the multiple kills, Reynolds wonders if a bear comes upon the animals wallowing in deep snow. Or begins an attack on a single animal, then gets hooked by other musk oxen that charge out from the group, and then responds in kind.

Understanding the dynamics between the species has never been more important. The rise in bear predation comes as ANWR musk oxen have crashed in number, from a high of 386 in 1986 and an average of about 325 in the early 1990s to an estimated 50 this year.

Where bear kills once accounted for virtually no musk ox deaths, predation took an estimated 13 percent of the ANWR herd in 2003.

Reynolds, who has studied refuge musk oxen for more than 20 years, cautioned that the overall decline in ANWR has been driven mostly by tough winter conditions, not bear predation.

Crusty or deep snow has been forcing the animals to work harder to find food. Possibly as a result, ANWR musk oxen haven't been producing many calves.

Adults have also started dispersing east and west into areas where the coastal plain is broader and might contain more winter food.

Overall, Alaska's musk ox population appears to be healthy, with 450 in the Arctic region and an estimated 5,000 in the state.

"It's never just one thing," Reynolds said. "Animals' populations are very complicated entities. But I think for Arctic ungulates or Arctic animals in general, winter weather is the major key."

Hunted to extinction in Alaska in the 1800s, musk oxen were reintroduced into the state in the 1930s and into ANWR in 1969. As the herd increased, the animals had 18 years of peaceful coexistence before the first predation was observed in 1987.
This lag time suggests that musk oxen needed to increase in density before bears began encountering them and figured out how to hunt them, wrote Reynolds and state biologists Harry Reynolds and Dick Shideler in the Ursus article.

The most dramatic event might have been in April 2000, when a federal pilot spotted several musk ox carcasses on the snow near the Canning River and thought he was witnessing the aftermath of poaching by human hunters.

But a state trooper from Coldfoot investigated and found that one bear had killed five musk oxen and a second bear had killed two in the same location and about the same time.

"I think that was the most dramatic event," Reynolds said.

The most recent instance occurred last April, when a state pilot caught sight of about 20 musk oxen scratching for frozen sedges in the crusty spring snow along the Canning River, Reynolds said.

Over the next few days, airborne scientists checking on the herd observed six musk oxen dead in the same location, all of them killed by grizzlies visiting the group on successive days.

Reynolds hopes to place more radio collars on ANWR musk oxen to investigate why many of them have been wandering out of the refuge. Maybe musk oxen that have dispersed will begin returning.

With numbers down so far, she also expects the number of bear kills to drop. In any case, Reynolds said the refuge staff has no intentions of intervening. In the refuge, musk oxen and grizzlies will be left to work it out.

"As far as I'm concerned, this is a natural event," Reynolds said. "It's not something that we've artificially set up. It's part of nature."

Daily News reporter Doug O'Harra can be reached at do'harra@adn.com .



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