BILLINGS, Mont. (AP) - Grizzly bears in the Yellowstone National Park area produced an average number of cubs in 2003 and appear to be expanding their range, according to a federal study.

Biologists last year found fewer females with cubs compared with a record 52 cubs in 2002, but the 38 cubs matches the average between 1997 and 2002, the Interagency Grizzly Bear Study Team reported.

"It's no cause for concern," said Chuck Schwartz, leader of the Bozeman-based study team. "It's just normal environmental noise and we'll probably see slightly higher counts next year."

The recovery of the bear population is about more than numbers, biologists say. It has more to do with available habitat, tolerance by people and the food supply.

The annual study, conducted since 1983, estimates that grizzly populations in the Yellowstone area have increased about 4 percent a year and shows grizzlies are consistently trying to move into new areas. Federal officials say there are probably 550 to 600 in and around Yellowstone.

Inside Yellowstone, bears probably occupy about as much of the landscape as they can, Schwartz said. When that carrying capacity is reached, grizzlies start reproducing in smaller litters and some begin wandering farther to find their own piece of land to call home.

"So bears are expanding their range," he said. "But it's not like they've picked up and left and we've got an empty hole in the middle."

Outside Yellowstone but within the adjacent recovery zone - a buffer of national forests and other public land that is relatively undeveloped - the population is growing by about 7 percent a year, Schwartz said.

"That's where we still have space for bears," Schwartz said.

Beyond the recovery zone, grizzlies start running into more private land and, soon, more trouble. Schwartz said death rates for grizzlies outside of the recovery area outstrip reproduction.

Studies will try to isolate the factors that most affect grizzly mortality, including road density and land development.

In 2003, 11 grizzlies in the Yellowstone ecosystem died from human causes, such as being hit by a car or shot. The figures from 2003 are the lowest since 1999, when seven grizzlies were reported dead because of people.

AP-WS-05-25-04 1138EDT