January 15, 2012 in Outdoors

Hungry wolf pack rearranges balance in Yellowstone Park

Brett French Yellowstone National Park
 

Members of Mollie’s
(Full-size photo)

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Typically content to stay in Yellowstone National Park’s remote Pelican Valley where they specialize in killing bison, Mollie’s wolf pack has migrated more than 20 miles to the Lamar Valley this winter, probably in search of food, and killing other park wolves along the way.

The wolves have explored the region as far back as 2000, and the pack’s founders hailed from the Lamar Valley, said Doug Smith, the park’s wolf biologist.

What is different is the extent to which they’ve migrated – all the way to the valley’s lower reaches, including Slough Creek – and why they’ve left their interior haven just north of Yellowstone Lake – a lack of snow.

This year’s territory shift also is unusual because the wolves have stayed longer than they typically do. Usually, they only visit the region for a few days. This time, they’ve already been there for three weeks.

Yellowstone has received little snowfall this year. The park opened only one entrance to snowmobiles in mid-December because other roadways were still bare or largely clear of snow. Only recently did the park finally allow snowmobile travel.

Snow is important to Mollie’s pack for hunting.

“Bison are the hardest prey for wolves to kill, so they need a little help from the snow,” Smith said.

Deep snow helps weaken bison, making it harder for them to feed and move. Wolves chase bison into deep snow where they’re easier to attack without the wolves being kicked or charged.

The 19-member Mollie’s pack – the largest in the park – has become well-known for its adaptations to killing bison. To bring down the 1,000- to 2,000-pound beasts, Mollie’s has nurtured some of the park’s largest wolves.

But even large wolves are no match for bison when there is little or no snow, like this year. What’s more, last year’s deep snow helped Mollie’s cull many of the weak bison from Pelican Valley, Smith said.

“The bison that are there now are the cream of the crop,” he said.

Despite the lack of snow, the interior region’s elk have already left, so they are no longer an available food source.

So Mollie’s pack traveled north, past the Grand Canyon of the Yellowstone and Mount Washburn, to reach Specimen Ridge that overlooks the Lamar Valley and its large herds of bison and elk. Since Specimen Ridge is the traditional home range of the eight-member Agate Creek pack, the intruders had to carve out some room.

“They’re throwing their weight around,” Smith said.

Smith’s team had radio collars on two of the Agate Creek pack members. Both were killed in mid-December when Mollie’s pack arrived, including the alpha male and a yearling male. That makes it difficult for Smith to keep track of the Agate Creek pack.

It makes no sense for his team to fly, dart and collar other wolves as they typically do at this time of year until there’s enough snow on the ground to slow down the wolves and making them easier to track.

“So the beginning of my winter is not starting off well,” Smith said.

This intrusion north isn’t the first this year for Mollie’s pack. In early December the pack moved into the Hayden Valley, just south of Canyon Village, and killed the alpha male of the 10-member Mary Mountain pack.

Seeing the opening, one of the subordinate males from Mollie’s pack shadowed the Mary Mountain pack for two weeks, keeping its distance. Eventually, the male was admitted to the pack, despite his relatives’ role in the death of the alpha male.

“That’s one of the joys of studying wolves,” Smith said. “They’re hard to predict.”

Mollie’s pack may also have been more restless this winter because of the absence of two wolves. One, a male, was killed when it was kicked in the ribs by a bison or elk. The pack’s alpha female has disappeared and a new female has stepped in to fill the void.

With the deaths, the park’s wolves unofficially number about 100 animals – comprised of 10 packs and eight breeding pairs. Last year, the wolf population stood at 97, so the numbers seem to have stabilized, Smith said.

More than 150 wolves inhabited Yellowstone around 2007 before the reintroduced population peaked. The natural occurrence of overpopulated wolves killing each other, malnutrition and mange are the likely reasons for the decline, park wolf experts said.


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