Field reports: Field report: As park elk decline, wolves turn to bison

PREDATORS – Bison are playing a larger role in the sustenance of Yellowstone National Park’s wolves as the bison herd has swelled and elk numbers have declined, according to the Yellowstone Wolf Project’s latest report.

“If wolves have a choice, they’ll always choose elk over bison,” simply because elk are easier to kill, said project leader Doug Smith.

Out of the 255 animals that wolves killed and that were detected by staff and volunteers in 2012, 62 percent were elk while 13 percent were bison. That’s the highest proportion of bison kills recorded since wolf monitoring began. Among the elk killed by wolves, 54 percent were newborn calves, 34 percent were cows.

One reason bison are playing a larger role in wolf diets is that their numbers swelled in Yellowstone to 4,600 in 2013, up 9 percent from 2011, while elk in the park’s northern range fell to about 3,900 from 4,100 in 2011.

Smith said wolf numbers inside Yellowstone seemed to have stabilized since 2008, following a peak in 2003 at 174 animals. In 2012, there were 83 wolves in 10 packs. Seven wolves were killed by other wolves and 12 were shot by hunters in the surrounding states of Wyoming, Montana and Idaho.

The number of wolves in the park is estimated at about 86 with more pups born than in 2012 and no park wolves recently taken in hunts in the surrounding states.

This year, very few wolves have spilled out of the park.

A less dense wolf population has meant no disease outbreaks since 2008 and fewer incidents of mange, which can cause wolves to lose their hair. In severe cases, they die.

The exception to the thriving interior packs is the Mollie’s pack, which fell from 19 wolves in 2011 to 10 in 2012. The pack was one of the first to consistently feed on bison. But by 2012 the pack’s age structure was not conducive to hunting bison – 13 of the 19 wolves were pups or yearlings and four of the other six were older females. Big, mature males are the most successful bison hunters.

The most unusual park wolf to die in 2012 was a 3- to 4-year-old male, 827M, that wandered more than 400 miles east where it was killed by a vehicle in South Dakota. It took less than two months for the wolf to make the journey from Delta pack range in the park’s remote southeastern corner.

The park’s wolves are some of the most popular and hated animals in the West. Because of where they live, they are also some of the most studied wolves in U.S. history.

The Agate Creek pack included female 471F, a nearly 9-year-old wolf that was killed by a rival pack and was about two weeks from whelping seven pups. The oldest wolf documented lived to 11.

The Agate Creek pack was unusual in that it had stable leadership, four alpha males and females in the pack’s 10 1/2 years. 472F was the alpha female for eight years, the longest-reigning alpha female on record.

Out of 18 Agate-born wolves collared over nine years, 11 went on to become the leaders of their own packs.

Delta pack contained some of the largest wolves in the park, including the alpha and beta males. When captured in February 2012, two yearlings weighed 145 and 106 pounds.

It’s estimated that 27,500 visitors to the park saw wolves in 2012, up from 25,000 in 2011.

Volunteers donated more than 6,800 hours to the project.