The two orphaned bear cubs that were returned to the wild last winter near Kaiser Pass have gone native.

In other words, they've up and vanished.

And California Department of Fish and Game wildlife biologist Dan Fidler is puzzled by their disappearance.

"It's kind of baffling," Fidler says. "Being that small, you'd expect they'd just hang around. But they booked it."

As you may recall, the two male California black bear cubs were found last summer near the High Sierra Ranger Station by campers who heard their shrieks and cries after a bow hunter illegally killed their mother, who had been known to ransack garbage bins and campsites for food. Distraught and malnourished, the two male cubs were unlikely to survive on their own.

So DFG biologists rounded up the siblings and transferred them to a facility in Lake Tahoe that rehabilitates orphaned and injured animals and birds. After about five months of fattening up on leafy vegetables, watermelon, sweet potatoes and live fish, they had grown from about 30 pounds apiece to 82 and 91 pounds. (To prevent the cubs from bonding with humans or associating humans with mealtime, handlers avoided contact and placed their food out of sight.)

In preparation for the cubs' return, Fidler dug out two dens, about 100 yards apart, on the road to Sample Meadow out of the hollow space below downed trees. The cubs were tranquilized and placed in the dens Jan. 10 with the hopes they'd keep snoozing till spring.

Well, that didn't happen.

About two weeks later, Fidler returned to the site and found both dens empty. The cubs had apparently woken up, pushed away the branches and bark that covered the openings and climbed out.

Fidler tried tracking the cubs, but the snow was too hard to leave any prints. Each cub had a radio transmitter attached to its ear, so he pulled out the telemetry unit to try to locate them nearby.

Not a blip.

"The day we placed them in the dens was the last we've seen of them, and I can't tell you how many miles I've driven looking," Fidler says. "It's a complete mystery."

The radio collars have a range of about one mile, so the biologist got in his truck and drove all the way to Florence Lake. (Remember Kaiser Pass Road had little or no snow last winter.) There was no sign of either cub.

Fidler returned in March and searched in vain around Edison Lake, Sample Meadow, Mount Tom and West Kaiser. He even sent a scientific aide to look for them in the Kaiser Wilderness on foot.

No dice.

"Never in my experience have I seen bears that age just up and disappear," Fidler says. "Not a set like that."

Fidler believes the bears simply moved on, perhaps to the east side of the Sierra or north toward Yosemite. It's possible that one (or both) of their radio transmitters fell out. It's also possible they died or were killed, although no bears with transmitters in their ears have turned up during the initial weeks of hunting season.

Would the cubs stick together or split up? The biologist isn't certain.

"Bears are social animals, but eventually they reach a certain point where they split off and do their own thing," Fidler says. "Whatever epic journey they've gone through, I kind of had it in my mind that they did it together."

What seems apparent, though, is that the two cubs did not pick up their mother's garbage-scavenging behavior. If they had, campers and campground hosts along Kaiser Pass Road surely would've noticed.

"They did exactly what we wanted them to do," Fidler says. "They're wild bears now."