Gray Wolves Impact Elk inside Yellowstone


Bull Elk. Photo by Steven Robertson

How wolves in Yellowstone have impacted their environment is an evolving story, but federal biologists have tried to match what they predicted a decade ago in an Environmental Impact Statement, with what’s happened regarding ungulate populations, hunter harvest, domestic livestock, and land use.

Research was published in the winter 2005 edition of Yellowstone Science. Authors include P.J. White, the park’s ungulate biologist; Doug Smith, the park’s wolf biologist; Terry McEneaney, the park’s ornithologist; Glenn Plumb, the park’s supervisory wildlife biologist; Mike Jimenez, the Wyoming wolf project leader for the U.S. Fish %26 Wildlife Service; and John Duffield, a professor of economics for the University of Montana.

Wolves vs. Elk Findings

  • Wolves are altering the abundance, distribution, group sizes, movements and vigilance of elk. There are some indications that these interactions may be causing new growth in willows as elk are kept on the move by wolves and don’t stay to browse in any one area very long.
  • Elk are the primary prey for wolves, comprising 92 percent of kills during the winter.
  • In the early stages of wolf recovery (1995-2000) predation effects were not detected because the elk count was similar to 1980-1994.
  • Counts of elk decreased significantly from 16,791 in winter 1995 to 8,335 in winter 2004 as the number of wolves on the northern range increased from 21 to 106. Factors contributing to this decrease include bear and wolf predation, increased human harvests, winter-kill (1997), and drought’s impact.
  • Wolves have not reduced mule deer or bison populations. Mule deer remain within 1 percent of a 17-year average of 2,014 deer, while the bison population grew 15 percent. There are no reliable estimates of moose populations following wolf restoration. Moose represent less than 4 percent of wolf diets in winter and only 26 instances of wolf predation on moose were recorded in Yellowstone during 1995-2003.
  • Kill rates by wolves in winter are 22 ungulates per wolf per year – higher than the 12 ungulates per wolf rate predicted in the ESA.
  • Since 2000, wolves have caused 45 percent of known deaths and 75 percent of predation deaths (not including human harvests) of radio-collared female elk on the northern range. By comparison, human harvest and winter-kill accounted for 30 percent and 8 percent respectively of the known deaths.
  • The average annual harvest of 1,372 elk during the Gardiner late elk hunts from 1995 to 2004 was higher than the long-term average of 1,014 elk during 1976-1994. Montana Fish, Wildlife and Parks has reduced antlerless permits by 51 percent from 2,882 to 1,400 during 2000-2004 and recently proposed 100 permits for 2006 – a 96 percent decrease from the 2,660 permits issued in 1995.