GOLD BEACH — As Dave Immel forces open a thick patch of huckleberries, the radio receiver clicking wildly through his earphones proves that five hours of climbing, pushing and sometimes crawling through dense forest finally has paid off.

Immel spies a large Douglas fir snag and quickly thrusts his backpack over the hole clawed into the snag’s base. A strange noise, like the sound of a spinning washing machine from two rooms away, drifts through the rotten wood.

"That’s the den and she’s in there," says Immel, an Oregon Department of Fish and Wildlife biologist. "That noise is the cubs suckling."

She is black bear No. 493744, and annual peeks like this one Tuesday into her winter hibernation could help unlock the secrets of why southwestern Oregon appears so rich in black bears.

This bear is one of six sows whose reproductive success will be traced over the next decade or more to determine whether Curry County’s black bears breed more like rabbits than typical bruins elsewhere in North America.

Predator researchers believe the Coast Range’s vast berry patches and diverse stands of oaks and firs provide such bountiful and consistent nutrition for these bears that they breed earlier, more often and more successfully than bears anywhere else on the continent.

"Some scientists believe that this area has the highest (bear density) in North America, but there’s no evidence now to corroborate that," says Immel, a veteran bear field researcher. "If we do have that amazing reproduction, we need an explanation."

The quest for that explanation brings Immel to bear No. 493744’s den deep in the Siskiyou National Forest about 18 miles east of Gold Beach.

Last July, ODFW biologist Clayton Barber trapped this bear in a nearby fir stand, where he anesthetized her, affixed a radio-transmitting collar around her neck and christened her bear No. 493744 in his capture log before releasing her.

Since then, technicians have flown over the area monthly to keep tabs on the bear via a receiver that taps into the collar’s specific radio frequency. Her general locations were mapped using a global positioning system, but coordinates alone won’t locate a bear.

Wearing a portable receiver dialed to No. 493744’s frequency, Immel leads a small posse of biologists and technicians through the Coast Range slopes loved by critters and loathed by humans for their steep banks and seemingly impenetrable brush.

After crisscrossing over ground never illuminated by direct sunlight, Immel emerges at No. 493744’s den and stuffs his backpack into the entry hole.

"Sometimes they tear up the backpack and take off," Immel says. "If they don’t, we can go in."

Immel has been diving into bear dens since winter 1993, when he headed a similar research project on Cascade Range bears east of Roseburg. About 150 dens later, he still has never been bitten or scratched.

"These bears are pretty docile most of the time," he says. "They usually just sit there and look at you. It’s hard to remember sometimes that these same bears in July will tear your arms off. So there’s always apprehension. You should have a healthy dose of respect for these animals."

And a dose of anesthesia.

Autumn Larkins, Immel’s assistant, loads a syringe with enough drugs to put the already groggy No. 493744 into a deep snooze, and screws the needle to a 4-foot-long pole. Larkins pulls the backpack away for perhaps the most dangerous moment in the encounter.

Immel sticks his nose into the entryway, then extends the needled pole inside.

Sometimes they thrash. Sometimes they bite. No. 493744, however, accepts her fate, leaning into the needle before Immel removes the pole and covers the hole with a tarp and backpack.

She lapses into a deep sleep. The suckling sound continues uninterrupted.

Immel then wiggles half-way through the opening and into the 5-foot-wide den, which is lined with fir boughs and is a cozy 55 to 60 degrees.

"Sometimes when you go in, all you see is hair," Immel says. "And some are cavernous, like a huge room. They’re never alike."

He paws at the snoozing bruin. She’s probably 120 pounds, with plenty of fat under her brownish hair. He pulls back her gums, running his fingers across her teeth. They still have points on them. No. 493744 is perhaps 3 years old.

The youngest bears with cubs in the Cascade study were 5 years old.

"(She) could be two litters ahead of the females in the Cascade Range," Immel says.

He rummages around and pulls out a single cub. It’s a male, or boar, only 2¾ pounds. Measuring his scalp hair reveals that he’s perhaps 5 weeks old.

Sows in the Cascade study averaged two cubs per litter, but just one cub for a mother this young is not unusual.

Larkins rubs ointment in the mother’s eyes to keep them moist during the hour or two she will remain drugged.

Barber, who will take over den-diving expeditions here for future years, loosens the collar he attached to No. 493744 last July.

"I’ve seen her before," he says, "and I’ll see her again."

And he’ll see many others.

The study calls for collaring and annually checking at least 21 bears from infants to as old as 20 over the next decade.

No. 493744 will remain part of the study until she dies. Her cub is the first to be plucked from a den for the Coast Range study.

When measurements are done, the cub is returned to the den, and the hole is covered with huckleberry branches for added warmth.

Immel cinches his knit cap over his ears for the next hour of climbing and crawling back to civilization.

"To me, it’s a pretty amazing sight," he says. "I never get tired of it."

Reach reporter Mark Freeman at 776-4470, or e-mail mfreeman@mailtribune.com

Some facts about Oregon’s black bears

Color: Most are black, but they can be cinnamon, chocolate brown and even white. Some sport a white chest patch.

Size: Adults average 180-200 pounds and usually measure about 5 feet from nose to tail.

Food: True omnivores, they eat anything from grass and bark to young fawns or even old or dead bull elk. Their primary diet consists of berries, nuts and bark. They are long-living and generally remain in seclusion other than when mating.

Mating habits: Adult females can have a fresh litter every two years, often remaining with the offspring for a year after birth. Litters consist of one to three cubs, which are hairless and about a pound when born. Most females need to be 120 pounds or larger to reproduce. It can take them 2½ to 5 years to develop into successful breeders.

History: Oregon’s population of black bears was down to an estimated 9,000 when state control over bear management began in 1936. Most bear mortality comes from hunting, either in season or because of landowner complaints of bear damage, chiefly to tree farms or livestock.

Population: The current, rough estimate of black bear population in Oregon is about 30,000. Curry County’s population is thought to be one of the densest in the West.