Photo: FHgitarre (cc)
Island closed on account of bears.
That was the message I got earlier this summer, when my husband and I set off for our annual trip to Lake Superior’s Apostle Islands. This national park is lousy with black bears. One of the islands, Stockton, is the bear equivalent of Manhattan — boasting one of highest black bear population densities in North America. Ironically, though, that wasn’t the island the bears had shut down. Instead, park visitors had been temporarily banned from setting foot on Sand Island, 4.5 square miles of forest and sandstone cliffs, shaped vaguely like a fat, upside-down comma.
The problem at Sand Island wasn’t an abundance of bears. In fact, the issues could be traced back to a single bear, or possibly two, Julie Van Stappen, the park’s chief of planning and resource management told me later. But rangers were worried about those bears’ behavior. Within the span of few weeks, human food had been scavenged, human tents damaged, and on one memorable occasion a bear tried to snuffle its way into a tent with the people still inside. Somewhere along the line, the bears of Sand Island had been conditioned to seek out humans, rather than avoid them.
This behavior puts the humans in danger. Big as they are, bears are easily startled by humans, and a startled bear is likely to attack anything it perceives as a threat. Six people in five different states ended up on the business end of a bear mauling just this month.
Rangers hoped that, by closing the island, they’d get an opportunity to recondition the bears — effectively teaching the animals to behave like proper, human-shunning wild creatures once again.
But first, they had to invite the truant bears to a barbecue.
All you need to condition an animal is a cue and a reinforcer — let them hear or see or smell something strange and link that something with a positive experience. The most famous example, of course, are the dogs trained by 19th-century physiologist Ivan Pavlov to associate the cue of a bell with the reinforcement of food. After a while, the bell would make the dogs drool, whether or not the food ever actually appeared.
That’s classical conditioning and it’s more about creating a reflex rather than getting the animal to do anything active. But, frankly, food is a great motivator for all kinds of behavior, including active learning. And that’s especially true for omnivores like dogs … or bears. When a bear learns to associate the presence of a colorful plastic tub with the discovery of tasty food, that’s really just a minor variant on classical conditioning, says Ralph Miller, a psychologist at Binghampton University. Like Pavlov’s dogs, the bear is getting a cue and the food reinforces the idea that the cue is important.
In the places where nature and human civilization butt up against one another, that fact translates into some big risks. Bears have three key activities in life. They breed, they hibernate, and they eat — and the first two activities are very dependant on how successful they are at the third. Because of that, bears are resourceful, willing to try new things, and willing to take a few risks if they get a reward for it, said Carl Lackey, a biologist with the Nevada Department of Wildlife. When bears cross paths with humans and aren’t chased away by bear spray or whistles, they quickly learn that humans aren’t something to fear. When they find food in those humans’ trash cans or tents, the bears learn to associate people and people things with the presence of a reliable meal. Those lessons increase contact between bears and people, which, in turn increases the chances of what rangers call “bear-human conflicts”. That’s dangerous for people, obviously, but it’s also dangerous for bears, who could end up shot when all they really wanted was your leftover hamburger.
But how do you get a bear — an animal that really wants food — to avoid an easily accessible source of food? One option is aversive conditioning, a system that tries scare bears away from people by using the same psychology that brought them to the trash can to begin with.
The Sand Island barbeque was a trap. Rangers filled a grill with bratwurst and made sure the tantalizing scent of grilled meat wafted beyond the campground area and into the woods. But they never really intended to share. Instead, they were trying to lure bears into human areas so that they could then chase the bears away from those areas using harmless little firecrackers called “whizz-bangs”. The hope: To take the cue of human stuff and change the reinforcement from a positive one — food — to a negative one — loud noises.
Conditioning can involve positive reinforcement or negative reinforcement. Aversive conditioning is based on the idea that, if positive reinforcement is bringing bears closer to people, maybe negative reinforcement can drive them away. There are a lot of different ways to do it and some methods are more involved than others. A lot of times, it simply involves waiting for a bear to show up in a place where it’s not supposed to be. Then, you scare it away, using whizz-bangs, or rubber bullets, or Karelian Bear Dogs, a breed that can be trained to chase bears from human sites and to give up the chase before they injure the bear.
In the 1980s, rangers in Yellowstone National Park tried a more Pavlovian approach. They captured known nuisance bears and put radio collars on them, so they could be tracked. When the bears came looking for food, the rangers would play a bird call — from a species that didn’t live in Yellowstone — and then shoot the bears with a rubber bullet. Over time, they thought the bears would start to respond to the bird call alone, immediately leaving any area where they heard it.
But it didn’t work. Not only did the bears never really develop a reliable conditioned response to the bird calls, they also didn’t change their behavior in response to the rubber bullets — at least, not in the long term. The rangers found that they could scare bears away from a site, and maybe make the lesson stick for a few weeks or a season. But, eventually, the bears would start coming back.
Experts say that’s a problem that’s come up in lots of studies of aversive conditioning. It only seems to be a short-term solution. And there’s a good reason for that: Negative reinforcement is a lot harder to pull off than positive reinforcement.
Think about trying to train a pet. My cats like to climb up on my planters because they like to eat my plants. Every time they climb onto the planter, there’s a positive reinforcement. When I see them do it, I squirt them with a water gun. But I can’t spend my life staring at the planter. When I’m not home, when I’m asleep, the cats have plenty of opportunity to keep eating the plant. The positive reinforcement is constant and reliable. The negative reinforcement is sporadic. So guess which one wins out?
The same thing is at work with bears, Ralph Miller said. To counter constant positive reinforcement, you have to create negative reinforcement that happens just as often. But that’s difficult. It’s also expensive. Meanwhile, depending on the age of the bear, you’re not just trying to reform a short-term habit, but rather a long history of lessons that the bear has been learning since it was a cub. Carl Lackey told me that bear mothers who frequent human areas train their cubs to do the same.
Success also depends on the environment. It’s a lot easier to convince bears to look for sources of food other than tents and trash cans when those other sources of food are plentiful. The Sand Island bears never came to the barbecue thrown in their honor, so the rangers never even got a chance to try out the aversive conditioning techniques. Instead, they just kept the island closed to people for a couple of weeks, leaving bears without access to the human food they craved. Meanwhile, the late spring finally kicked in, berries blossomed, and the bears found a different food source.
There’s a lesson in the story of Sand Island — taking away the positive reinforcement of human food is more effective than trying to create a negative reinforcement by frightening bears away from that food. That’s actually why national parks have developed such stringent rules about what visitors are supposed to do with their trash, how they’re supposed to store food, and how they’re supposed to behave in bear country. It’s all about removing the positive reinforcement.
In fact, the most successful reduction in bear-human conflicts is based on his principle. In the first half of the 20th century, Yellowstone National Park averaged 138 bear-caused property damage incidents and 48 bear maulings every year. It was also a time when bears were getting LOTS of positive reinforcement from human behavior. People hand-fed bears along the highways. They left food in coolers and picnic baskets where bears could easily reach it. There were even bleachers installed at local trash dumps, so people could come and watch bears eat their garbage. Generations of bears had learned — go where the people are and you will be fed.
Then, beginning in the late 1960s, Yellowstone started to change. Dumps were closed. Trash cans were bear-proofed. Rangers educated campers about securing their food and started cracking down on tourists who fed the bears. There were still problems with some of the older bears, but the younger ones learned — there’s no reward to be had for pestering people. Today, despite the fact that human visitors have tripled, Yellowstone’s bears are involved in fewer than a dozen incidents of property damage every year and average only a single mauling. In the end, the best way to retrain bears is to retrain people.