The packs are back
Dan Hansen
Staff Writer
Reintroduction of wolves is rewriting the list of winners and losers among
wildlife in Yellowstone National Park
A day ago, members of the Druid wolf pack brought down an elk in
Yellowstone National Park. Now, its naked ribs jut above the grass like
the tips of a king’s lost crown.
The wolves gorged themselves and returned to their den to feed the young
of the pack, through regurgitation. But the carcass is not done providing
nourishment.
Thirteen ravens peck at the remains, still finding scraps of dried meat
among the bones. A golden eagle rests nearby, having already visited the
carcass. And as Dan Stahler watches through a spotting scope, a coyote
scatters the birds and begins tugging at the remnant hide.
Most likely there have been foxes on the carcass, too, and maybe
grizzlies. Certainly magpies. And insects are no doubt taking their share.
“There are hundreds of carrion beetle species alone,” says Stahler,
Yellowstone biologist for wolf recovery. “That carcass will affect the
soil microbes, so it will affect the (grass), too.”
Called a “trophic cascade,” this process of lesser animals benefiting from
the kills of top predators happened a lot less frequently before wolves
were reintroduced into the park in 1995.
The last of Yellowstone’s original wolves were shot and poisoned in 1926.
That left grizzlies, coyotes and other less-efficient killers as the most
common predators in the Lamar Valley, a corner of Yellowstone so rich in
wildlife that it’s often compared to Africa’s Serengeti plains.
Having reproduced prolifically since reintroduction, wolves now number
about 130 within the park, giving scientists a rare opportunity to watch
how the return of a native species affects an ecosystem.
Some of the relationships are far less obvious than a crowd of
“klepto-parasites” — that’s what scientists call thieving scavengers like
ravens — gathered around a dead elk. Rodents, beavers and badgers all
have been affected by the reintroduction of gray wolves.
Canis lupis is even affecting the trees.
Scientists estimate that quaking aspen historically covered about 5
percent of Yellowstone’s Northern Range, which includes the Lamar Valley.
That dropped to about 1 percent in recent decades, and most of the
remaining trees are old-timers. Streamside willows also were reduced.
“No large stands of cottonwoods have been established on the Northern
Range in 120 years,” according to a recent report published in the journal
BioScience.
Now the trees appear to be coming back, as evidenced by several acres of
knee-high willows at the confluence of the Lamar River and Soda Butte
Creek.
Ever-cautious scientists say it’s too early to give credit to the wolves,
but they acknowledge that the evidence is strong, since much of the new
growth is occurring in areas the packs use as travel corridors. Elk no
longer loiter in those areas, nibbling away the trees as they emerge from
the earth.
Where there are willows and water, there are beavers, and researchers
recently documented four colonies in the Northern Range. They found none
in 1996.
The beavers’ return is due largely to an effort to reestablish them in the
Galatin National Forest, just north of the park. “But it’s also because
the willows are back,” Stahler said.
Although other impacts haven’t yet been documented, more willows should
eventually mean more insects, drawing more song birds, who will find more
nesting sites. More insects and shade may even mean more trout in streams
that already merit blue-ribbon status with anglers.
In the absence of wolves, coyotes were the park’s top dogs, organizing
packs with defined territories. In the three years following
reintroduction, the coyote population in the Northern Range dropped from
80 to 36, due to attacks by wolves.
Fewer coyotes mean more ground squirrels for lesser predators.
“We have more foxes than we did before,” said wildlife guide Carl Swoboda,
who’s in the park nearly every day. “We’re seeing a lot more badgers and
eagles and hawks.”
Park biologists also are starting to note an increase in pronghorn
antelope, whose fawns are a favorite prey of coyotes.
Wolverines, which scavenge carcasses, may increase in Yellowstone,
according to the April BioScience report that was written by Yellowstone
wolf project leader Doug Smith and two other biologists.
Cougars appear largely unaffected, although one researcher documented
wolves killing a litter of four cougar kittens in recent years.
Elk make up about 90 percent of the diet for Yellowstone wolves, and are
killed at a rate of about 15 a year for every wolf. About 40 percent of
those dead elk are calves, 40 percent adult cows and 20 percent adult
bulls.
Yellowtone’s northern elk herd has declined since 1995, but it’s unclear
how big a role wolves played in that decline. Biologists note that many
elk were lost to severe weather during the winter of 1996-1997. Since
then, the region has been plagued by drought that has also affected the
herd.
Before attacking an adult elk, the wolves “try to get an elk herd to move
and run, so they can see the one that’s slow, the one that’s limping,
whatever the vulnerability,” Stahler said. “The whole idea of a predator
strengthening a herd, making it stronger by weeding out the weak is very
much true.”
Volunteer and paid researchers who study skeletal remains have found that
the average age of the cow elk killed by Yellowstone wolves is 14. That
compares to an average age of 6 among those killed by Montana hunters just
outside the park. Marrow in the bones of wolf-killed adults often is
depleted of nutrients.
Swoboda recently showed a typical elk skeleton to wildlife watchers from
California. Although it hadn’t been aged by researchers, the cow’s teeth
were worn down to its jawbone, a sign of old age.
But it is the youngest elk that fall prey in spring.
The peak of calving season is June 1 and “there are a lot of predators
waiting,” Stahler said. They include grizzly and black bears, coyotes,
cougars and golden eagles, in addition to wolves.
Yellowstone’s bison, meanwhile, are largely unaffected by predators.
Trying to attack a bison calf is a dangerous game, often bringing a
counter-attack from adults that can weigh a ton.
One wolf pack, in the heart of the park, has resorted to killing bison in
winter, when elk are scarce. But such kills often come at great cost;
researchers watched last winter as one wolf was killed and two others
injured as the pack brought down a bison bull.
Wolves have killed relatively few of Yellowstone’s moose and deer, and
there are no documented kills of bighorn sheep.
Scientists expect changes similar to those experienced in Yellowstone to
follow wolves as they expand their range in the Northwest. Already,
biologist Holly Akenson, who lives at a research station deep in Idaho’s
Frank Church-River of No Return Wilderness, has noted an increase in aspen
that she thinks can be attributed to wolves.
“Wolves have really changed everything,” she said.