The wildlife biologist Lynn Rogers had logged thousands of hours studying North America's black bears. He had shot them with tranquilisers before fitting them with ear tags or radio collars. He had drawn their blood and mapped their DNA. And he had tracked their movements with pins on maps.

But none of that had allowed him to really know the creatures. When he did get close to a bear in the wild the animal was usually terrified, caught in a live trap in the woods.

Rogers eventually realised he couldn't hope to know bears unless he won their trust. And so he abandoned scientific detachment and took the daring and controversial step of forming relationships with his study animals, using food to gain acceptance among an extended bear family inMinnesota.

Gaining the trust of the bears has given him a close-up insight into their behaviour and social organisation as well as allowing Rogers to explode myths about them. Contrary to popular belief, for example, he contends that the bears are not violent and do not like honey.

"Those are the accepted ways of studying bears. You catch a bear, you take a lot of measurements," Rogers said. "It's interesting information but it doesn't give you the detail that a person really wants to know about bears – what they are really like, how they live."

The extraordinary relationship between Rogers and his research subjects is revealed in a BBC film, Bearwalker of the Northwoods, which airs on Wednesday night.

The film-makers have shot the first footage of bears mating and they got close enough to record wild bear cubs purring while suckling.

The film opens with Rogers – a lean, white-haired man who is now 70 – hiking through the woods of north-eastern Minnesota about to commit what most North Americans grow up believing is one of the cardinal sins of outdoor life: drawing within a paw-swipe of a mother bear and her cubs.

Rogers approaches the mother bear den slowly and deliberately. "It's me, bear, it's me," he calls out.

The adult female he calls Juliet, swats a few times at the opening of the mud and wood den. Rogers is unfazed. "She is not a mean bear. She is just a nervous bear, but she will calm down," he tells the camera. And within a few moments, it looks as if Juliet is so relaxed she is about to nod off to sleep.So far as biologist-bear relations go, Juliet is close family. Her sister, June, is Rogers's most prized research subject, the source of much of his knowledge about bears. It is clear that June occupies a far bigger place in Rogers's heart than any of her assorted relatives and offspring.

"June in her eight years has become ever more trusting. You can see how she is not wary of me at all. She is completely trusting," said Rogers.

In the years Rogers has tramped through the Northwoods he has abandoned just about everything he knew, or thought he knew, about bears. They do not like honey. They are not even that crazy about berries or nuts – provided, of course, there is a nice rich stash of ant larvae in the vicinity.

And they are not ferocious. Rogers is adamant about that. He said he has never heard a bear roar or even growl, and that in all of his years of close proximity to the animals he has never been seriously hurt even though in his early years he displayed what he calls "bad bear manners".

The bears he knows are timid creatures. Defensive postures, such as swatting their large paws on the ground, are mistaken for aggression by many people.

"In my 42 years of working closely with bears and testing every no-no, I have not found a way of getting a bear to attack. The more I push them the more they try to get away. They might want to nip and slap, but it is not an attack, it is just a way of fending me off so they can find a way to escape."

It's humans who are the more dangerous animal, he said. "If you look at the statistics, one black bear out of a million kills somebody. With grizzly bears it's one in 50,000. Among humans it's one person out of 18,000 kills somebody. So you could see why I would feel a lot less comfortable in the city than in the woods next to a bear."

Rogers's methods have made him controversial with fellow bear researchers and he does not have a significant publishing record in academic journals. Tim Ginnett, an associate professor of wildlife who has been working at the University of Wisconson-Steven's Point black bear research project for the last nine years, said that feeding the animals runs the risk of changing the very behaviour you want to study. "We want to understand how they behave and operate in a natural ecosystem. And feeding them - to my way of thinking - kind of disrupts that so it's not an approach we use," he said.

Rogers is no sentimentalist. Even after devoting 40 years of his life to the back bear of Minnesota he is under no delusion that his interest is reciprocated. Even June does not really like him, he said.

"June she has no feelings for me. If she had feelings i think she would want to seek out company like a dog does its master," he said. "But she doesn't think of me in those terms. I'm just the guy that brings her a treat once in a while and that she can ignore and not pay any attention to and that is what makes her so valuable to science."

• Bearwalker of the Northwoods is on BBC Two at 8pm on Wednesday 28 October