Crawling into southwestern Oregon bear dens to monitor the bruins' progress is the ultimate don't-try-this-at-home wildlife experiment.

Dave Immell slips through the small hole at the base of a hollow Douglas fir snag and into the tight confines of a black bear den. He inches forward until his chest rests atop the sleeping giant within. He paws around the sides of the tranquillized sow until his left hand finds a suckling blob of fur and claws.

Immell wiggles to freedom with his find. In his hand he cradles a miniature predator, its already-immense paws splayed forward, it's eyes locked on Immel, the first human this cub has ever seen.

The bear delivers a menacing squint, as if it is thinking, "I know what you look like. I know what you smell like. If I smell you again, you're dead."

"I've felt that," Immell says. "I don't know if it's true, but I've sensed they know me. Like, 'Yeah. I know this guy and he's done some things I didn't necessarily like before.' Bears can be weird like that."

What passes for weird is actually quite wild in the den-diving world of Immell, who each spring gets personal with a set of Oregon black bears — all in the name of science.

As an Oregon Department of Fish and Wildlife biologist, Immell has spent the past 15 springs climbing into more than 300 bear dens as part of a research project unlocking secrets about black bear reproduction in a remote part of Oregon.

From late February through March, Immell surveys the reproductive successes of nine radio-collared black bears in the rugged mountains of eastern Curry County. He's tracked many of these bears for years, entering their dens to count, weigh, measure and tag the suckling cubs they bear each season.

Over time, the data is helping researchers validate a hypothesis that the rugged western portion of the Rogue River-Siskiyou National Forest has some of the most dense black bear populations in the country because of good forage and habitat.

Gathering the data is the thrilling part of this outdoor science project, and Immell occasionally brings along a lucky outsider who gets to feel what it's like to wiggle into a bear den and quite literally get nose-to-nose with one of Oregon's apex predators.

It's the ultimate don't-try-this-at-home exercise. And it's one that never gets old.

"Even after all this time, it still puts a little adrenaline in your body," says Immell, 52, of Roseburg.

Today, his adrenaline is focused on black bear No. 493744, a sow trapped and radio-collared six months earlier in the forest 18 miles east of Gold Beach. 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 are mapped using a global positioning system, but coordinates alone won't locate a bear.

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

After hours crisscrossing ground never illuminated by direct sunlight, Immell pokes his neck through the brush and stops. He's face-to-face with No. 493744, her head swaying like a pendulum in the den's door not two feet from Immell's nose.

Immell stuffs his backpack into the entry hole. Then, nothing moves. The gentle sound of suckling from inside the den is all that fills the air.

"About 15 percent of the time, they tear up the backpack and take off," Immell says. "If they don't, we can go in."

These aren't the musings of a madman. With all the bears in all the dens he has entered in southwest Oregon, Immell's never been bitten or scratched.

"Bears are pretty docile in the den," 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 healthy dose of anesthesia.

Immell loads a syringe with the drug Telazol and screws it into the end of a 4-foot aluminum pole. He then pulls the backpack away for perhaps the most dangerous moment in this encounter.

Immell sticks his nose into the entryway, then extends the needled pole inside. Sometimes the bears thrash. Sometimes they bite. No. 493744, however, accepts her fate, leaning into the needle before Immell removes the pole and covers the hole with a tarp and backpack. She lapses into a deep sleep. The suckling sound continues uninterrupted.

Immell then wiggles halfway through the opening and into the 5-foot-wide den, which is lined with fir boughs, making it a cozy 55 to 60 degrees.

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

Like a beat cop, he pats down the snoozing 120-pound bruin. Quickly, he finds his quarry.

The lone cub is a male, or boar, only 2¾ pounds. Measuring the scalp hair reveals the boar's age. Sows in the Cascade study average two cubs per litter, but just one cub for a mother this young is not unusual. Ointment rubbed into the mother's eyes keep them moist during the hour or two she will remain drugged.

When measurements are done, the cub is returned to its safe haven.

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

Fellow ODFW biologist Clayton Barber loosens the radio collar, offering growing room for No. 493744 during the year ahead. As the posse prepares to drag and claw their way back to civilization, Immell covers the hole with huckleberry branches like he's tucking in a newborn.

"I've seen her before," Immell says, "and I'll see her again."