Nathaniel Brooks for The New York Times

NORTH ELBA, N.Y. — It was built to be impenetrable, from its “super rugged transparent polycarbonate housing” to its intricate double-tabbed lid that would keep campers’ food in and bears’ paws out

Bears and campers do not usually interact, and when they do it is usually over food.

Four years ago, New York State began requiring overnight campers to use bear canisters in the eastern High Peaks, a sublime wilderness favored by backpackers and black bears alike. Several national parks, including Yosemite, also require canisters.

Before they used canisters, campers often stored food in bags, typically hung from cables slung between trees, which inadvertently made for one-stop shopping for bears.

“They had learned that when they saw a bag in the air, there had to be a rope someplace and they learned to bite or slice the line,” said Neil Woodworth, executive director of the Adirondack Mountain Club, a conservation and recreation group.

The number of “negative human-bear interactions,” according to the Department of Environmental Conservation — mainly incidents in which bears approached people looking for food — dropped to 61 last year in the eastern High Peaks from 374 in 2005. But, of course, there was a problem with the solution.

BearVaults, one of several canister brands, are favored by many backpackers because they are light and can be opened with bare hands; most others require a coin or screwdriver. Like other brands, BearVaults must pass the zoo test, in which bears are given a certain amount of time to try to break into a canister filled with food.

Similar to a childproof medicine bottle, the BearVault 350 and 400 models can be opened by pressing a tab that allows the camper to screw off the lid. But reports began coming in from campers a few years ago that BearVaults were being broken into. State wildlife officials began suspecting Yellow-Yellow, one of a number of bears they have tagged and tracked as a way of studying the behavior of the more than 5,000 bears roaming the Adirondacks.

In most BearVault break-ins, Yellow-Yellow’s radio collar indicated she had been in the area. Eventually, campers began spotting her from afar rifling canisters. There have been no reports of her threatening anyone.

So last year Mr. Hogan introduced the 450, a two-pound cylinder costing about $60, and a larger version, the 500, each with a second tab. On them, a camper must press in one tab, turn the lid partway, then press the second tab to remove the lid. “We thought, ‘O.K., well, one bump didn’t work so maybe two bumps will thwart her,’ ” he said.

But Yellow-Yellow figured that lid out, too.

Last month, her achievements were noted in an article in Adirondack Explorer. And she now appears to have apprentices; campers have reported seeing other bears getting into their BearVaults.

“Yellow-Yellow seems to be the most adept at defeating it,” said David Winchell, a spokesman for the Department of Environmental Conservation’s Region 5, which covers the High Peaks. “Certainly, she is the most commonly observed in the area when it’s happening."

It is not certain exactly how Yellow-Yellow plundered campers’ Italian sausages and granola bars, but she apparently depresses one tab with her teeth, turns the lid, uses her teeth on the second tab, and then opens it. At the Adirondack Mountain Club’s High Peaks Information Center here, where campers can rent canisters, an example of a defeated BearVault is on display: a bear’s teeth have left deep gouges in the hard plastic lid, as though it were putty.

“I don’t think she’s twisting it with her paws,” said Chuck Bruha of the Mountaineer, a camping-goods store in nearby Keene Valley. “We think she’s biting the lid and twisting her whole head.”

Ben Tabor, a state wildlife technician who has tracked Yellow-Yellow, said the evidence on the canister supports that theory. (He watched her tackle a BearVault two years ago, although he was too far away to determine her method. ) He doubts, however, that she has out-of-the-ordinary intelligence. “I don’t think she’s smarter than most bears,” he said. “I think she’s had more time to learn.”

Mr. Tabor emphasized that Yellow-Yellow, while tenacious with the BearVaults, is shy around people; she runs from them. He worries that her prowess could lead to pressure to kill her. In 2006, the agency had to kill a 350-pound black bear that had cornered campers with food inside their lean-tos, although no one was hurt. “It would be ridiculous for us to remove Yellow-Yellow at this point,” Mr. Tabor said. “She’s not bold. She doesn’t charge. She steals food but runs away when confronted.”

Mr. Hogan is working on a prototype of a new model, the 550, for next year. State officials have agreed to test it by filling it with aromatic food and depositing it on Yellow-Yellow’s turf. “She’s the whole reason we’re doing this,” he said.

And from the BearVault website:

RAE LAKES CANISTER SWAP PROGRAM:

BearVault models BV350 and higher are now fully approved for use in all SIBBG controlled areas and can be used without restrictions in the Rae Lakes drainage basin in Kings Canyon National Park and throughout the Sierras. These models can be identified by a large red decal on the lid with the model number displayed prominently on this decal. If you do not have this red decal on the lid, then you have one of the earlier models listed below that are restricted from use in the Rae Lakes drainage basin in Kings Canyon National Park.

Currently hikers to the Rae Lakes drainage basin Rae Lakes drainage basin in Kings Canyon National Park cannot use the following BearVault bear canister models: BV110B, BV200, BV250 or BV300. There were 8 break-ins during the summer of 2005 and until more experience is gathered this summer, the use of the above models is not allowed in this area. There are currently no restrictions on the use of these model BearVaults elsewhere in SIBBG controlled areas- they can be used throughout the Sierras and all other locations.

To accommodate BearVault customers who wish to hike in the Rae Lakes drainage basin in Kings Canyon National Park and who own one of the earlier restricted model canisters listed above, the following swap-out program is available. 

Starting in early June, when a hiker shows up at either the Road’s End Permit Station/Cedar Grove Ranger Station (tel 559-565-3790) in Kings Canyon National Park or the Lone Pine Ranger Station (tel 760-876-6200) to pick up their back country permit for the Rae Lakes area of Kings Canyon National Park, you must inform your permit issuer that you need to exchange your bear canister. If the hiker has a BearVault model BV110B, BV200, BV250 or BV300, the ranger will then exchange your existing BearVault with a new full size BearVault model while supplies last. The supply of full size BearVaults will be replenished throughout the summer, however occasionally the permitting stations may run out. This will allow the hiker who already owns an early model BearVault to enjoy the Rae Lakes area with an approved BearVault canister.

This swap-out program is only available for hikers picking up their backcountry permit to hike the Rae Lakes drainage basin in Kings Canyon National Park. If you are going elsewhere, your current BearVault canister is fully approved and can be used without restrictions.

And for a link to the Interagency Grizzle Bear Program, click here.