The study also found, contrary to popular perception, that the black bears most likely to kill are not mothers protecting cubs. Most attacks, 88 percent, involved a bear on the prowl, likely hunting for food. And most of those predators, 92 percent, were male.This article in the New York Times includes a valuable video by bear-attack researcher Stephen Herrero, who talks about patterns in bear attacks.
I used to believe the "mother bear defending her cubs" idea too. Then, in the early 1990s, M. and I worked as contractors each summer for the Bureau of Land Management, counting Mexican spotted owls (and other owl species) in southern Colorado.
Since our work involved hiking from late afternoon into darkness, we had a number of encounters with black bears.
The first time we encountered a sow with two cubs in a narrow canyon, we immediately retreated. The we climbed up on a nearby rocky outcropping. We could hear the bears flipping rocks in the little creek, looking for food, and grunting at each other. Eventually, it became dark, and they had to be still out there somewhere. But we could not afford to wait all night, so we flicked on our headlamps and hiked out with many an anxious glance backwards. Never saw the bears.
Another time, another deep canyon, we met a mother and cub. Mom sent the cub up a tree, while the last we saw of her was her butt going over the ridge. We continued higher up the canyon to our calling spot. Meanwhile, the cub started to wail—a sound somewhere between the crying of a 100-pound baby and the bray of a donkey.
After trying unsuccessfully to find another way down that did not involve passing the cub, we eventually started back the way that we had come. By then Mom had come back, and they were both gone.
All other bear encounters were inconsequential. Most bears are shy.
Prof. Herrero points out that bears are still mostly "benign," when you consider that there are on average two attacks a year from a North American bear population of 750,000-800,000.