When Yellowstone National Park’s aching cold and deep snow claims the lives of winter-weakened bison, predators like wolves are one of the beneficiaries.
“Wolves know the bison are going to die so they wait and scavenge a lot,” said Doug Smith, Yellowstone’s Wolf Project leader.
Yellowstone estimates on average that about nine out of every 100 bison die each winter. With the park’s bison population now around 5,500 animals, that means roughly 500 bison could perish this winter. With adult bison ranging from 1,000 to 2,000 pounds, those carcasses will be a substantial source of protein for park predators and scavengers, especially top predators like wolves who in the winter don’t have to compete with hibernating grizzly and black bears.
“Yellowstone is a pretty good place to be a wolf,” Smith said.
Studies in the park’s Northern Region have estimated that wolf survival is due in large part to that reliable source of bison meat, composing as much as one-quarter to one-third of a wolf’s scavenging activity. Without bison carcasses, Smith said the park’s wolves may not have enough to eat in the winter.
Such a large source of food may be one reason the park contains the longest-known pair bond between two wolves ever recorded. Alpha male 712 will be 12 years old this March, an incredibly long life considering that on average Yellowstone wolves live only to age 5.
Wolf 712’s mate is a white female popular with photographers. Because she’s never been captured and collared, Smith isn’t sure how old the white wolf is, but she’s been with her black mate for more than seven years. Wolves begin breeding at 2 or 3 years old, so the female is almost as old as 712.
“It’s a cool story,” Smith said. “They’re probably the most famous wolves in the park.”
The two lead the Canyon pack, which roams the area around the Grand Canyon of the Yellowstone and Hayden Valley, north of Yellowstone Lake.
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“This pack has been very comfortable near developed areas, exemplified by their use of a highway culvert to stash pups in 2008, denning near park headquarters in Mammoth Hot Springs in 2009, and regularly using roads as travel corridors during the winter months,” according to the Yellowstone Wolf website.
Given their familiarity with the park and its bison, Smith said the alpha pair’s winter routine is likely to include checking places where bison are known to die in hopes of finding a large, already dead meal.
“I can guarantee you they are going to all of their old spots,” he said.
Smith also goes to all of his old spots in the park in the winter when searching for wolves to dart from a helicopter. Darting wolves allows him to collect physical information and fit animals in almost every pack with GPS collars. So far this winter, though, cold and wind has kept his crew from helicoptering aloft.
That’s bad news for information collection because the last two years were also poor for darting and collaring. What’s even more frustrating is that out of the 12 wolves the park did capture last winter, collars on five of them failed within a few months of deployment. Annually the park attempts to collar 15 to 20 wolves, with at least one collar in each pack. Twenty to 22 collared wolves is the long-term average, so Smith said 12 is disappointingly low.
As a result, in two of the Northern Region’s larger packs, one has no collar and the other contains only one wolf with a working collar. The problem with the lack of collars was demonstrated in November and December when much of the Junction Butte pack disappeared from the park and wandered into Montana. While there, three members of the pack were legally killed by hunters north of the park. Park researchers are trying to understand the impact that the hunting seasons in surrounding states have on park wolves. Another three park wolves from the 8 Mile pack were also shot this hunting season, Smith said.
At last count, Yellowstone contained about 100 wolves in 10 packs, a population that has remained fairly stable since 2008. Lower wolf densities may be one reason that the park’s wolves haven’t had an outbreak of disease for eight years, defying researchers’ predictions that distemper would strike every three to seven years.
“Wolves are coming into equilibrium with the environment,” Smith said.