JACKSON (AP) - A new study suggests that elk from Grand Teton National Park migrate early to the National Elk Refuge each fall and are more successful at avoiding hunters.

Many elk migrate when deep snow forces them to move. But a study by Bruce Smith, a retired refuge biologist, concludes that elk leave Grand Teton for the refuge when park forage dwindles, not when snow pushes them south.

Smith tracked elk with radio collars and found that hunters took fewer elk from Grand Teton than from Yellowstone and other areas. He also sampled vegetation and found that forage levels, on average, were down 62 percent when elk migrated out of Grand Teton.

"One would not think that they would have to leave," said Smith. "Snow isn't limiting their ability to forage. By sampling vegetation, we were able to determine that it was probably initiated by the depletion of forage west of Snake River, more so than by snowfall."

Smith said forage in Grand Teton dwindles when elk from Yellowstone and the Teton Wilderness move to Grand Teton in the early fall, staying there for days or even weeks.

"It greatly increases the number of hungry mouths there that are feeding on the vegetation that is left," Smith said.

The Grand Teton elk that move southward in response tend to be more successful at avoiding hunters, in part by choosing routes through housing developments where hunting isn't allowed. They also have a better chance of surviving the winter because they find plenty of ungrazed, irrigated forage at the south end of the refuge.

Smith said elk don't consciously decide when and how to migrate. But he said that elk with better survival tactics reproduce more and pass their behavior to offspring.

Refuge officials opened part of the refuge this fall to hunters with bows and limited-range guns. The goal is to target the Grand Teton elk that have faced little hunting pressure.