FAITH LAPIDUS: Black bears are more common in North America than brown bears or the brown bear known as a grizzly. Many experts also say black bears are by far the least aggressive.

Published reports say up to nine hundred thousand black bears live in North America. Mr. Herrero says the animals are safer to be around than dogs, snakes or bees.

Black bears have killed about two people a year over the past ten years. The researchers blamed most of the deadly attacks on bears searching for food. The report says eighty-eight percent of bears in those attacks acted like a predator. In other words, they captured and fed on other animals. And ninety-two percent of the bears that showed predatory behavior were male.

Each of the deadly attacks considered predatory was made by a single bear acting alone.

BOB DOUGHTY: Mr. Herrero says people who have training can learn to recognize a predatory bear. He says a demonstration of strength does not mean that the bear means to kill a person.

Mother bears with cubs are a good example. When they see people, he says, they often run at them and make a lot of noise. The professor says, "They want you to think they will eat you alive. But they almost always stop." He advises people to back off quietly.

By comparison, he says the predatory male follows people. The bear senses that the people are targets, perhaps for food. Then it silently attacks its target. Mr. Herrero advises aggressive action. "Fight back," he says.