"Hunting is a learned behavior for mountain lions -- they are not born knowing what their prey is," he said. "We're not hunting them, we're not chasing them, so they have the chance to observe us as noncombatants. They have a chance to learn we are a prey species."
Doug Updike, a senior wildlife biologist for the California Department of Fish and Game, disagrees.
"If you look at other states that don't have the population we do, there are still attacks on humans," Updike said. "There are still attacks, whether people are hunting or not."
Leslie Chow, a researcher in Yosemite National Park who studies mountain lions, said Fitzhugh also doesn't explain why mountain lions still attack hunters in Montana or Idaho.
He agrees the lions are in some cases adapting to humans, and "young lions who are hungry may be willing to experiment a little more. But I'm not sure as a race they are coming to regard humans as prey."
Chow said a female mountain lion was euthanized last fall after she walked through Curry Village in Yosemite Valley, which is frequented by thousands of tourists daily, and made herself visible to humans three or four times over a period of eight years. She was probably feeding her young, he said, and was hunting raccoons in the park, not people.
Fitzhugh, who is familiar with the Yosemite cougar case, said, "Yeah, but she was also watching the cabin where schoolkids were regularly staying. She was 10 feet away from a restroom they had to use at night."