LIGONIER, Pa. - After a drive up a narrow logging road in the heart of the Allegheny Mountain range, a group of game wardens and others faced a 20-minute hike up a steep ridge over rocks and fallen branches.

They were heading for a den with hibernating black bears as part of an effort to monitor their numbers and health.

Amid a thicket of vines and saplings, the group found more than they were looking for. Instead of a mother bear with two 8-week-old cubs, they came across the mother with three yearling cubs.

A conservation officer fired a tranquilizer gun at the mother and three cubs to sedate them for study, but the cubs scampered away and only two were hit.

The game wardens and a dozen volunteers gave chase through dense brush and rounded up two of the cubs a few hundred yards away, when they collapsed from the drug. The third was never caught.

Bear biologist Mark Ternent carefully laid the sleeping cubs, each the size of a large dog, rump to rump atop freshly fallen snow and dug out his medical equipment. After a moment of concern that the smaller cub might be in respiratory distress from the sedation, Ternent took their vital signs and pronounced the bears in fine health.

The expedition was part of the annual den sweep conducted statewide by the Pennsylvania Game Commission during the animals' winter hibernation. This season, wardens visited 115 dens and tagged 600 bears to get a head count, fix radio collars, and perform health checks on the state's black-bear population.

The bears are thriving at a time when other species are facing threats. The state's brown bats are dying in record numbers from a fast-spreading fungal disease, and several species of water birds - among them black-crowned night-herons and great egrets - are suffering because of habitat loss from development.

But the black bears of Pennsylvania - once almost wiped out by heavy logging and overhunting - are experiencing a landmark resurgence. Over the last four decades, their numbers have quadrupled, from 4,000 in the 1970s to roughly 16,000 today, according to Game Commission estimates.

"The '70s was the dark period," said Ternent, the state's bear caretaker since 2000. "By 1920, the land was cleared of timber, and for many years there was unregulated hunting." The Game Commission responded and helped turn the tide by halting hunting seasons for several years during the 1970s.

Today, Pennsylvania, among the Eastern Seaboard states, has the greatest black-bear range, with most bears living in the thick, sprawling forests of the state's northern tier. Bear dens have been found as close to the Southeast as Berks and Lehigh Counties.

Game Commission spokesman Jerry Feaser said the state had not reached a point where there were too many bears for the forest to support, but in some areas, such as the Poconos, there are more bears than humans can tolerate, leading to expanded hunting seasons.

Game officials attribute the bear growth to reproductive luck and intensive bear-management efforts aimed at expanding the bear population in the right places. For instance, here in the southwestern section of the Allegheny Mountains, bears were reintroduced to help repopulate this 16,000-acre forest in Westmoreland County.

"Pennsylvania has higher reproductive success than other states. Where bears in other states have one or two cubs, ours have three or four," said Feaser, who credits the higher cub count in part to the state's bountiful food supply. "In addition, we've limited the bear-hunting seasons and made efforts to get bears into adequate habitats."

Increasing numbers of human-bear encounters in areas with growing human populations such as the Poconos have helped focus the bear-management plan. It's Ternent's mission to strike a balance: setting hunting goals to curb the numbers of nuisance bears in more developed areas, while ensuring adequate food and forest cover in more remote areas with high bear densities.

Last year, 3,354 bears were killed during the three-day hunting season in 52 of the state's 67 counties. An additional 800 bears were killed by hunters in areas determined to have a high number of nuisance bears. Ternent said he believed that the number killed - about 20 percent of the population - had helped keep the population in proper balance. About 300 additional bears die each year after being struck by vehicles.

Feaser said bears that turn up occasionally in the Philadelphia area are usually young males displaced from the Pocono region or New Jersey. While there have been bear sightings in Bucks County, Feaser could not recall any recent incidents in the Philadelphia area. Ternent, though, said a bear was trapped last year in Montgomery County.

On the day of the den expedition here last month, Ternent and other game wardens, trailed by a group of curious onlookers, hiked through the brush atop Chestnut Ridge amid spring snow flurries.

The discovery of the yearling triplets took the group by surprise.

"I thought there was a lot of hair in there," said Ternent. One cub bounded away. But Ternent was able to dart the other cubs and the mother as she lay hibernating in her den, a kind of lean-to of brush and logs.

With the clock ticking on the tranquilizer, Ternent stapled the last tag on the 60-pound male bear cub's ear. "There you go, 33581," he said. "That's how you'll be known for the rest of your life."

After checking on the 143-pound mother just coming out of her sedation, Ternent tucked the yearlings back in the den, where they would get a few more weeks of shut-eye and spend their final days with their mother. Sometime this month, the young ones will head off into the forest on their own.

Contact staff writer Amy Worden at 717-783-2584 or aworden@phillynews.com.