Three bears meandered up from the woods near Leesburg Pike yesterday morning, nodded to some of their human neighbors near Colvin Run, then headed back to the wilderness of Fairfax County.

The black bears didn't menace anyone or do any damage to homes or property on Thompson Run Court and Leesburg Pike, in the Great Falls area. Experts said it is unusual but not unheard of for bears to wander into suburban neighborhoods around Washington. It's likely the bears followed a series of rivers through the mountains of the Shenandoah and into the back yards of Fairfax County in search of food and water, experts said.

"My guess is that this one family group moved up the rivers," said Michael Vaughan, professor of wildlife science at Virginia Tech. "That's not that far, and we are seeing bears starting to extend out of the [Shenandoah] region."

Vaughan said the bears probably began their journey during the summer drought, when food in the mountains was particularly scarce. "There was a real response to the drought," he said. "Some bears came out of the hills to lower elevations, and these could be some of those bears."

Fairfax police said a homeowner in the 9700 block of Leesburg Pike spotted the bears Wednesday night and again yesterday morning in her back yard. Officer Jayne Woolf said two of the bears appeared to be adult-size, and one was smaller, possibly a cub.

An animal control officer went to the neighborhood and saw two bears standing on a bike path next to Thompson Run Court and Middleton Ridge Road. The bears then retreated into Colvin Run Stream Valley Park, Woolf said.

Animal control and police officers swarmed into the area but couldn't locate the small traveling band. The hilly area around Difficult Run stream and Colvin Run stream is dense with brush and briers, interrupted by the occasional tree, and animal control experts eventually decided that the bears probably didn't have a den in the area. They decided against any effort to capture the visitors.

"It's not unusual for them to do this," Woolf said, "because they're foraging for food. It's normal for them to follow stream beds," of which there are many in the northern section of the county.

Officers knocked at houses in the Middleton neighborhood, warning residents to bring in any remaining pumpkins or outdoor trash containers that might act as a lure. Woolf said that black bears are basically shy and would tend to avoid humans, but that if this group has a youngster in tow, the bears could act aggressively, so anyone who spots them should call police.

Residents said they have seen their share of deer, foxes, rabbits and snakes in the neighborhood over the years, but never a bear.

Fairfax animal experts told police that bears have been spotted in the county before and that at least one was trapped by animal control officers last year. Woolf said the Virginia Department of Game and Inland Fisheries would consider trying to trap yesterday's travelers only if they are spotted again near a residential area. They would then be returned to an area with fewer humans.

Bears are omnivores and will eat anything from a dead animal to nuts and berries. They are ravenous as they prepare for winter hibernation, and an oak tree with a plentiful supply of acorns would be enough to lure a group of bears into a residential neighborhood, Vaughan said.

Vaughan speculated that the family of bears may have been scared from the woods by hunters.

Regardless, experts said the three are definitely of the black bear variety, the only kind found on the East Coast. The far larger and more dangerous grizzlies, also known as brown bears, live exclusively west of the Mississippi River. Black bears grow as big as 5 to 6 feet and weigh anywhere from 200 to 600 pounds.

Jim Fraser, professor of wildlife science at Virginia Tech, cautioned that the bears may have been trying to find a winter home. "We've found them nesting under people's porches around habitation sometimes," he said.