BILLINGS, Mont. - When young elk die on Yellowstone National Park's northern range, more often than not the killers are bears, not wolves, according to results of a three-year study.

The survey of elk calf mortality indicates that bears were responsible for 53 percent of the kills, while wolves were responsible for 12.8 percent and coyotes 11.1 percent, according to preliminary results.

The outcome came as no surprise for biologists who study predator-prey relationships around the country. In areas where bears and ungulates share a piece of land, bears tend to seize opportunities to eat young calves.

"The results are exactly what you'd predict," said Ed Bangs, wolf recovery coordinator for the U.S. Fish and Wildlife Service.

The Yellowstone study was launched in 2003 after a decline in the number of elk counted during annual surveys on the northern range. Between 1994 and 2004, the elk count dropped from 19,035 to 8,335.

The number of calves per cow - a ratio used to determine the herd's reproductive rate - has also dropped to the lowest levels in decades.

Biologists said several factors have contributed to the decline, including predation, hunting and drought, but they wanted to know more about what killed elk calves on the northern range.

Between May 2003 and August 2005, 151 calves were captured and fitted with ear transmitters. Of those, 100 died within the first year of life. Those working on the study then tracked down the young elk and determined how they died.

Over the three summers from 2003 to 2005, bears killed 58 young calves and wolves killed 14. Coyotes ranked third, with 12 kills.

Bears tend to hunt in gridlike patterns in the spring and summer, searching for young calves that might be hiding. Wolves are more likely to kill in the fall and winter when elk gather in larger groups.

Leaders of the study cautioned against extrapolating the results to other elk herds in Yellowstone.

After wolves were reintroduced to the Yellowstone ecosystem, there was heated debate over what impact they would have on the elk population, including those on the northern range.

While wolves certainly play a role in controlling the elk population, the picture is more complicated, biologists say. Wolves, bears, weather, hunter harvest and other factors contribute to elk declines year-round.

The latest information about what kills calves, though, isn't likely to change many people's minds about wolves and elk, Bangs said. Those who think wolves are decimating the population will continue to think so, and those who think that wolves have little or no impact will continue to believe so, he said.

The study was conducted by Yellowstone, the U.S. Geological Survey and the University of Minnesota.

Researchers will continue to track tagged elk calves through the winter of 2006.

The $107,000 study will be the subject of a Ph.D. dissertation and will likely go through peer-review this year or next.