Motion-sensing cameras have shed new light on nighttime mountain lion activity in a hilly 1,189-acre preserve five miles west of the Stanford campus.

The infrared cameras, which are triggered by movement, have recorded more than 40 photos and videos of cougars since September 2009, most between dusk and dawn.

The pictures show that the big cats are most active in the area between May and September.

A group of Stanford postdocs and graduate students assessed the risk of a human-puma encounter in the area, known as the Jasper Ridge Biological Preserve. They estimated that mountain lions are roaming the preserve about a quarter of the time, but that "there are likely at most only one male, one female and possibly several cubs whose territory includes the preserve."

"Based on historical statewide data, the annual risk of being attacked by a mountain lion in Jasper Ridge is 1 in 10 million," the authors wrote.

Video copyright Jasper Ridge Biological Preserve of Stanford University