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By Dan Vergano, USA TODAY
Whodunit? The big, bad wolf? Old Man Winter? A scientific mystery starring wolves, adversarial weather and a declining elk herd is playing out at Yellowstone National Park.
An elk stops traffic in Yellowstone. The elk population is declining in the park, but scientists can't agree on the reason.
By Erik Petersen, The (Cody, Wyo.) Enterprise via AP
Oh, and people — hunters — are possible suspects, too.
The elk population in North Yellowstone has dropped to about 8,000 from almost 17,000 in 1995. That was the year wolves were reintroduced into the 2.5-million-acre federal park in Wyoming, which overlaps the border of Montana and Idaho.
The northern herd contains just a fraction of the 120,000 elk believed to dwell in the park region, and Yellowstone's Northern Range is just 204,000 acres. But this region is of particular interest to scientists because it has the largest wolf population, about 106 of the park's 171 wolves in 2004, making the elk there the most vulnerable herd.
The wolves' return, which is seen by the National Park Service as a success in restoring natural balance, has drawn fire from ranchers and residents. A plan by Wyoming officials to allow unregulated hunting of wolves in some areas outside of the park — hunting is not allowed on Yellowstone lands — has been rejected by the U.S. Fish & Wildlife Service.
The wolves were expected to take a bite out of the northern herd, but the decline is greater than expected, says biologist John Vucetich of the Michigan Technical University in Houghton.
Hunters, who target elk that leave the park, have blamed the wolves. But researchers, including Vucetich, say the problem isn't that simple.
In an analysis in the current edition of the ecology journal Oikos, for example, Vucetich and park service colleagues examined weather, hunting and wolves as factors in the elk decline. Yellowstone has had seven years of drought and a severe winter in 1997 that killed many elk.
They found that weather and hunting are mostly to blame.
Biologist Mark Boyce of Canada's University of Alberta and colleagues reach similar conclusions in an upcoming paper in the journal EcologicalModeling. Montana increased the "hunter harvest" quota on elk that leave Yellowstone grounds, issuing a higher-than-ever 2,882 hunting permits in 2000. A decline in the elk herd was thus guaranteed, Boyce says, even if wolves were not present.
A review in the September Biological Conservation journal comes to a somewhat different conclusion. Authors P.J. White of the park service and Robert Garrott of Montana State University in Bozeman say wolves and hunters share the blame.
And the wolves influenced the behavior of Yellowstone's northern elk, Boyce says. For example, they have adopted protective strategies, such as moving more often and in larger groups.
In the park, some biologists have suggested that increases in aspen, willows and cottonwoods may be the result of fewer elk foraging less often in areas where wolves lurk, White says.
Like every good mystery, a little-suspected culprit may be hiding in plain sight: bears.
In the Yellowstone Science journal, U.S. Geological Survey ecologist Dave Mech and his colleagues concluded this summer that "grizzly and black bears, rather than wolves, are having a greater impact on neonatal elk calf mortality than any other predator."
Zigzagging through fields where young elk lie, bears kill roughly six times more calves than wolves do, the ecologists found. Elk calves are uniquely vulnerable: They tend to stay in place near danger instead of running. In May and June, bears hunt through Northern Range calving areas for them, looking for an easy meal.
Grizzly bears are another Yellowstone-area success story that might have come at the expense of elk, Mech says. Since 1987, the predators' numbers have increased from 150 to more than 600 in the region, according to federal estimates, and many converge on the park's northern calving areas.
In fact, the grizzlies have done so well that the Interior Department has proposed taking the Yellowstone region's bears off the threatened species list under the Endangered Species Act. They've been on that list since 1975.
More years of watching wolves are needed to get a handle on the elk's decline, says Ken Hamlin of Montana's Fish, Wildlife & Parks department. He's inclined to blame the wolves, noting that elk in areas with few, or no, wolves, seem to do better. And species that wolves prey on far less often, such as mule deer and bison, haven't seen big drops in numbers, he says, despite going through the same drought and severe winters.
A steep drop in elk-hunting permits triggered by the herd's decline seemed to offer a chance to ascertain to what degree hunters have been responsible, Hamlin says. But wolf numbers also have dropped steeply in the park this year because of disease, throwing off the experiment.
"Nature just sticks her foot in there every time," Hamlin says. "We may never have any really final answers."
Whodunit? The big, bad wolf? Old Man Winter? A scientific mystery starring wolves, adversarial weather and a declining elk herd is playing out at Yellowstone National Park.
An elk stops traffic in Yellowstone. The elk population is declining in the park, but scientists can't agree on the reason.
By Erik Petersen, The (Cody, Wyo.) Enterprise via AP
Oh, and people — hunters — are possible suspects, too.
The elk population in North Yellowstone has dropped to about 8,000 from almost 17,000 in 1995. That was the year wolves were reintroduced into the 2.5-million-acre federal park in Wyoming, which overlaps the border of Montana and Idaho.
The northern herd contains just a fraction of the 120,000 elk believed to dwell in the park region, and Yellowstone's Northern Range is just 204,000 acres. But this region is of particular interest to scientists because it has the largest wolf population, about 106 of the park's 171 wolves in 2004, making the elk there the most vulnerable herd.
The wolves' return, which is seen by the National Park Service as a success in restoring natural balance, has drawn fire from ranchers and residents. A plan by Wyoming officials to allow unregulated hunting of wolves in some areas outside of the park — hunting is not allowed on Yellowstone lands — has been rejected by the U.S. Fish & Wildlife Service.
The wolves were expected to take a bite out of the northern herd, but the decline is greater than expected, says biologist John Vucetich of the Michigan Technical University in Houghton.
Hunters, who target elk that leave the park, have blamed the wolves. But researchers, including Vucetich, say the problem isn't that simple.
In an analysis in the current edition of the ecology journal Oikos, for example, Vucetich and park service colleagues examined weather, hunting and wolves as factors in the elk decline. Yellowstone has had seven years of drought and a severe winter in 1997 that killed many elk.
They found that weather and hunting are mostly to blame.
Biologist Mark Boyce of Canada's University of Alberta and colleagues reach similar conclusions in an upcoming paper in the journal EcologicalModeling. Montana increased the "hunter harvest" quota on elk that leave Yellowstone grounds, issuing a higher-than-ever 2,882 hunting permits in 2000. A decline in the elk herd was thus guaranteed, Boyce says, even if wolves were not present.
A review in the September Biological Conservation journal comes to a somewhat different conclusion. Authors P.J. White of the park service and Robert Garrott of Montana State University in Bozeman say wolves and hunters share the blame.
And the wolves influenced the behavior of Yellowstone's northern elk, Boyce says. For example, they have adopted protective strategies, such as moving more often and in larger groups.
In the park, some biologists have suggested that increases in aspen, willows and cottonwoods may be the result of fewer elk foraging less often in areas where wolves lurk, White says.
Like every good mystery, a little-suspected culprit may be hiding in plain sight: bears.
In the Yellowstone Science journal, U.S. Geological Survey ecologist Dave Mech and his colleagues concluded this summer that "grizzly and black bears, rather than wolves, are having a greater impact on neonatal elk calf mortality than any other predator."
Zigzagging through fields where young elk lie, bears kill roughly six times more calves than wolves do, the ecologists found. Elk calves are uniquely vulnerable: They tend to stay in place near danger instead of running. In May and June, bears hunt through Northern Range calving areas for them, looking for an easy meal.
Grizzly bears are another Yellowstone-area success story that might have come at the expense of elk, Mech says. Since 1987, the predators' numbers have increased from 150 to more than 600 in the region, according to federal estimates, and many converge on the park's northern calving areas.
In fact, the grizzlies have done so well that the Interior Department has proposed taking the Yellowstone region's bears off the threatened species list under the Endangered Species Act. They've been on that list since 1975.
More years of watching wolves are needed to get a handle on the elk's decline, says Ken Hamlin of Montana's Fish, Wildlife & Parks department. He's inclined to blame the wolves, noting that elk in areas with few, or no, wolves, seem to do better. And species that wolves prey on far less often, such as mule deer and bison, haven't seen big drops in numbers, he says, despite going through the same drought and severe winters.
A steep drop in elk-hunting permits triggered by the herd's decline seemed to offer a chance to ascertain to what degree hunters have been responsible, Hamlin says. But wolf numbers also have dropped steeply in the park this year because of disease, throwing off the experiment.
"Nature just sticks her foot in there every time," Hamlin says. "We may never have any really final answers."
Shoot them in the ass!
