“The canister, the locker — all of those things were basically invented here in Yosemite,” says Rachel Mazur, Chief of Wildlife and Visitor Use for Yosemite National Park.

As for the problem that these inventions were created to solve?

“The problem was not invented here,” Mazur says, “but we sure did a good job of making it a tough one.”

“In your car, you turn to ‘Classic Rock;’ here you get a bear”

Ryan Leahy is on patrol in Yosemite Valley. Leahy looks kind of like a cop — sunglasses, a uniform with a vest full of pockets. He’s armed with a radio and binoculars. Leahy’s a biologist; he’s patrolling for bears.

As we slowly drive along a back road in Yosemite Valley, he sticks a hand-held antenna out the window. There are up to 500 bears in the park, and Leahy and his team have put GPS and radio collars on a handful of them to be able to track them.

“Essentially they have radio frequency and we have a receiver,” he explains. When Leahy listens to different frequencies using his antenna, he can hear the beeping noise coming from different bears’ collars. “Like in your car you turn to 104.1 classic rock, but here you get you get a different bear.”

The beeping speeds up. “The bear’s pretty close,” Leahy says.

There’s plenty of natural food for bears to eat in Yosemite, but they’ve learned that swiping coolers and grocery bags is just easier. So Leahy and his team monitor the bears to try and prevent them from ever getting a taste.

Leahy’s park radio interrupts our quiet listening. One of Leahy’s crew members is trying to get a hold of him, because a mamma bear and cub have been reported in a campground on the opposite side of the park. Then his work cell phone rings. It turns out there’s even another bear down here in the valley. He’s got to move quickly.

“If there's a bear in the campground in the middle of the day going after human food,” he explains, “it's going to probably get worse fast.”

He pulls over into a parking lot so he can make a plan, which turns out to maybe be a bad idea because now he’s a sitting duck for tourist questions. In the middle of all this chaos, a park visitor approaches his truck window. “Hey, where’s Half Dome?”

You know, the giant granite monolith visible from most places in Yosemite Valley.

Leahy is nothing but professional. “After you take a left at the stop sign, look right on the bridge; you'll see Half Dome. It's huge. You can’t miss it.”

More than four million people visit Yosemite each year, most only for a day. Many are first-timers and don’t even know their way around the park, let alone how to behave in bear country.

Bears take advantage of that ignorance, which is why Leahy’s got to get on the road, and drive to the other end of the park to keep these bears from getting into people’s food.

This is the reality of bears and humans trying to coexist in Yosemite.

So how did we get here?

From bear-feeding shows to “nuisance bears”

In the early 1900s, tourists started visiting Yosemite year-round. This was a time before garbage trucks and even plastic garbage bags were invented, and the tourists needed somewhere to put their trash.

“It was crazy!” Rachel Mazur says. “They would have a dump, and that's where the garbage would go.”

Before Mazur worked as Chief of Wildlife in Yosemite, she wrote a book about the history of bears and humans in the park. She says the bears quickly figured out that they could go to the dump and eat campers’ food scraps. Then, the concessionaire for the park figured it could make money off of tourists who’d love to see bears up close and personal.

“They'd put bleachers up, bus people in, have on spotlights, and you'd have twenty, thirty bears in there, feeding off the trash but also fighting each other,” Mazur says, and basically becoming conditioned to humans and our food. The dumps drew bears out of the wilderness into Yosemite Valley. They started reproducing in larger numbers because they got so many calories from human food.

Visitors were getting too close to the bears and getting injured, and the park realized it had to make some changes. It ended all bear feeding shows in the 1940s and closed the dumps in 1970.

“But you can't just close dumps and expect these bears that are food-conditioned and used to humans to disappear back into the forest,” Mazur says.

When the dumps closed, the bears turned their eye toward the campgrounds and visitors’ cars. This lead to even more injuries and rangers killing what they called “nuisance” bears.”

It wasn’t the type of job that the rangers had signed up for. They wanted to figure out a way to keep bears wild and away from human food, so, Mazur says, they started experimenting. They created special lids for garbage cans, and metal lockers for campers to store their food, with latches complicated enough that they were sure bears wouldn’t be able to use them.

Yet bears are very smart and they figured out a way in. The rangers tweaked the designs more, adding carabiners and inventing new latches. Mazur has a whole stack of these old bear locker designs outside her office in Yosemite Valley; she calls it the “bear locker graveyard.”

Staying ahead of the “wily bears”

While rangers experimented with bear-proof storage for car campgrounds, more and more tourists were heading out to hike in the wilderness. This was the late 1960s and the start of the environmental movement. Many young people wanted to go backpacking.

George Durkee was a ranger in Little Yosemite Valley, the popular backcountry area behind Half Dome. Hikers would hike from the valley up to these woods and stay overnight, leaving the next day to climb the famous granite monolith. They didn’t have anywhere to store their food while they camped.

“You would get five or ten people minimum having their food taken every night,” Durkee remembers.

Other campers were about to set out for weeks-long trips on the John Muir Trail. They didn’t take kindly to the idea of losing all their food to bears before such a big trip. Durkee remembers one upset camper chasing a bear when it ran off with his food sack.

“It was one of those cartoon moments,” Durkee laughs. “You see the bear suddenly realizing, ‘Wait a minute, I'm a 200 pound bear. I don't have to put up with this!’” The bear turned around and swatted the guy across the chest.

Others campers tried using their food as pillows, which Durkee says is a very dangerous idea. “On the one hand, you want to say, ‘This is natural selection at work!’ But you don't want people to get hurt.”

Campers would complain to Durkee when they lost their food to bears, so he and other rangers started experimenting with different ways to hang food away from bears’ reach. First, he tried tying the food between two trees, but bears would chew through the rope and pull down the food. Then, Durkee invented something called the counterbalance system. He would throw a rope over a tree branch and hang two food bags of equal weight on each end; that way, there was no rope for the bears to chew through. Instead, bears would climb high into the tree and drop down onto the food from above, knocking it to the ground. Then the bear would run off with the food bag.

“It’s just one thing after another trying to stay ahead of the wily bears!” Durkee says.

The park tried installing metal poles with hooks that campers could hang their food on, but those got knocked down by an avalanche; then the park helicoptered heavy bear lockers into the backcountry.

“They tried everything," Rachel Mazur says. Until finally, “This idea of the canister came about.”

The bear canister: a portable, cylindrical container that bears cannot open, and that holds about five days of food. It looks sort of like a drum. These days, anyone backpacking in Yosemite must use one.

The idea was invented by Barrie Gilbert, a behavioral ecologist, who was researching bears in Yellowstone and got horribly mauled by a grizzly. The bear pulled the scalp off his head, ripped off his ears and took out an eye.

After he healed, he decided to send his graduate student to research black bears in Yosemite instead, figuring he’d be safer there. But the graduate student kept losing his food to the bears! (It’s better than losing an eye, but still a problem.) Gilbert wanted to invent a way for his student to be able to bear-proof his food.

He got the idea while watching a nature show on TV. He saw a frustrated lion pawing at an ostrich egg, trying to eat it, but its shape kept the lion out. That’s when Gilbert “just had this ‘A-ha’ moment,” Mazur says. Gilbert realized if someone could design a contraption that bears would have trouble getting a grip on, and make it lightweight, backpackers might be able to use it to bear-proof their food.

Gilberts’ colleagues working in Yosemite took the idea and ran with it. They hired a machinist from Visalia to make prototypes and gave them to bears at the Fresno Zoo to see if they could break them open.

They ran through many prototypes, testing them both on bears and humans. “You're trying to find something that can keep a bear out but that humans can use and will” use, Mazur says. “We learned, for example, if there's more than two hand motions, people won't do it.”

When it comes to bears, nothing is foolproof. A few black bears have figured out a way around these canisters. There’s a famously smart bear in the Adirondack mountains that taught herself out how to open one of the canister models. Back here in Yosemite, a clever bear realized she can roll canisters off a cliff to break them open. Then she climbs down to get the contents. “It just drives us nuts!” Mazur says.

That’s just one individual bear and the park was able to close that area off from camping. The people on Mazur’s team sometimes have to relocate young bears or even adult bears that have become too conditioned to human food.

“It feels like the ultimate betrayal,” Mazur says. When visitors don’t bear proof their food, it’s really the bears who pay the price.

That’s what’s driven rangers and researchers over the years to invent these bear-proof contraptions. Yet even once the park knew that the canisters and lockers worked, it took decades to get the funding and the support to put all the infrastructure in place and get visitors to use them.

“If we backslide, everything backslides”

Now, with tons of education and enforcement, and requiring the use of bear lockers and canisters, Yosemite has reduced their human-bear incidents, from a high of 1,500 a year to under 50.

Mazur says, that’s exciting. “But what's also amazing is in the old days, all we did was bear management - nothing else.”

Remember, she’s technically the Chief of Wildlife, not just bears. Now she’s able to focus on reintroducing endangered species like the Sierra Nevada bighorn sheep and yellow-legged frog. But Mazur says, the park still has to stay on top of bear management.

“If we backslide, everything backslides,” she says. “We won't just lose our grip on the human-bear issue. We'll lose our grip on all the good wildlife work that we're doing.”

Mazur says, it’s ultimately up to the tourists to behave properly in bear country. She says, many times campers have told her they didn’t really believe how bad the bear-human food issue was until they lost food to a bear themselves.