YELLOWSTONE NATIONAL PARK — A waning moon hangs low in the morning sky as park biologists Doug Smith and Daniel Stahler pack their gear for another day in the field.
It’s day 28 of the Yellowstone Wolf Project’s annual December push, a 30-day blitz to collect as much information as possible about the park’s wolf population and how they interact with their prey, from elk to bison to the occasional hapless raven.
“We’ve worked very hard over the last 15 to 16 years to understand the annual cycle of wolf killing and prey selection, particularly elk,” said Smith, the park’s senior biologist and head of the Yellowstone Wolf Project. “That’s one of the big flash points for having wolves back in the Northern Rockies.”
The balance between wolves and elk in and around Yellowstone National Park is a subject that gets people talking, fueling a debate that’s lingered since wolves were reintroduced to the park in the mid-’90s.
But biologists with the Yellowstone Wolf Project are looking past the impressions to the science. For nearly two decades now, they’ve recorded wolf predation rates and prey selection in the park, looking for clues to the season, the weather, and how nature finds a balance in the subtle dance between predator and prey.
After a morning briefing at park headquarters in Mammoth, the team set out for the field, heading east across the park’s northern tier to check in with three observation crews hunkered down in the morning chill.
North Butte and the Blacktail Deer Plateau, their first stop, rises as a nub of rock and brush, a good place to get out of the wind and peer across the expanse of meadow and woods. On this day, visibility runs for miles in the frigid mountain air.
The butte is staffed by Rebecca Raymond, whose voice crackles over the radio. She gives a play-by-play account of the Blacktail wolf pack operating to the west.
Seen through a scope, one wolf is warming on a rock. The others are out of view, but the pack howls into the morning, proclaiming its presence with a long and resonant call.
“This is a key area for this pack,” said Smith. “They’ve spent the last three weeks in this region here. It’s a big elk route out of the park, so this pack does quite well here.”
‘Harder to kill’
At this time last year, researchers recorded 97 wolves inside Yellowstone. The 2010 study found a 43 percent decline in the park’s wolf population from 2007, because of what Smith describes as a smaller, healthier elk herd.
From 2009 to 2010, the study found, six packs had dissolved or left the park, while two new packs had formed. The park is now home to 11 wolf packs and six loners.
This northern quadrant of Yellowstone was first settled in 1996 by the Leopold pack. It has since been replaced by the Blacktail pack, which enjoys a relatively small but rich territory near Mount Everts.
Competition for range and prey is fierce in the park’s northern tier, a corridor through which elk and bison migrate toward lower valleys as winter sets in and the snow piles up.
But this winter has been mild so far, and without the snow to push them, the elk aren’t moving as they have in past years.
The ungulates remain strong and healthy, forcing wolves to adapt. They’ve been sitting on kills longer than they would in late winter, when it’s easier to take down vulnerable prey.
“In early winter, elk are in their best condition, so they’re harder to kill,” said Stahler, a Wolf Project biologist in Yellowstone. “By late winter, elk and other ungulates become weak, so we believe weather influences both kill rates and prey selection.”
Wolves can’t kill anything they want, Stahler notes. They seek out vulnerable prey — animals weakened by poor nourishment, age or injury.
Thirty miles east at the crest of the Lamar Valley, another Wolf Project team has had a busy morning. The Lamar Valley pack made a kill just before sunrise, taking down an old cow elk on the road above the icy Lamar River.
“It definitely happened before it got light,” said Colby Anton, a biology technician with the Wolf Project. “There’s some running wolf and running elk tracks off in the snow. It looks like they chased it down. All the organs were gone when we got there.”
Enough of the carcass remains for continued feeding. At dawn, the team cut the carcass into thirds and dragged it off the road and up a hill, where the wolves and other scavengers will continue feeding on the remains.
Smith notes that the elk’s teeth are worn to the nub. He believes the animal was pushing 25 years, which is old for an elk.
“This is early winter and so the elk are in pretty good shape and they’re hard to kill,” Smith said. “If you make a kill right now, it’s worth a lot to you. You hang with it and consume everything you can from it, because going off and making another kill isn’t going to be that easy.”
Another observation team near Tower Junction has trained its spotting scopes on Specimen Ridge, where members of the Agate Creek pack have been sitting by a bull elk carcass for the past four days.
Near the Yellowstone River in Hayden Valley, biologists have observed another wolf pack as it returned to a bison carcass killed three weeks earlier. Such desperation isn’t as obvious in the spring, Smith said, when prey is easier to come by.
“This time of year, when a kill gets made, it’s incredibly valuable and important,” he said. “If you go out and can’t make another kill, you go back to an old one. They know what the pickings are. This is really indicative of what time of year it is.”
Smith said the Wolf Project recorded 268 wolf kills last year, including 211 elk, 25 bison, seven deer, four wolves, two moose, two antelope, two grizzly bears, four coyotes and two ravens.
But it’s the elk that get most attention. Hunters complain of fewer elk for the taking.
“We know that wolves impact ungulate herds like elk, but so do many other factors, like weather, human predation, habitat change and fires,” said Stahler. “It’s a very complex thing, so we’re trying to figure out this one element of it and see how that fits into the bigger picture.”
Stahler notes that the park’s elk population has declined roughly 50 percent since wolves were reintroduced. But while wolf predation has played a role in the decline, he said, so have other factors, including predation by other animals, management of elk outside the park, and weather, which influences both the quality and quantity of forage.
“We still have one of the highest elk densities around in a North American herd,” Stahler said. “Predators tend not to cause their prey to go extinct. Evolutionarily, that would be a bad strategy.”
Smith believes that wolf and elk populations have reached an equilibrium.
“Systems tend to fluctuate around an average or equilibrium,” Smith said. “Thirty years ago, elk didn’t have any predators, other than a lower-density bear population and some human hunting outside the park.
“You can argue that an elk herd can also benefit from the return of the wolf, by having a system that supports a herd that can fit into the available resources.”
“Wolf and elk issues are controversial, and we’re trying to get real data to support the patterns, so we have a good idea of the ecosystem effects of wolf recovery,” he said.