Katmai National Park and Preserve, AlaskaOn a sunny day in August, more than two dozen brown bears are gathered at Brooks Falls, in Alaska’s Katmai National Park, to feast on sockeye salmon. Thousands of the fish are delayed or stranded here by the six-foot waterfall, a hurdle they must leap over to return to their native spawning grounds upstream. The bears occasionally growl at each other, competing for the best fishing spots.

A huge male known as Lefty, who has white scars on his flank from past battles with rivals, perches on the upper rim and snags salmon out of mid-air. Every few minutes, Lefty catches one and ambles to a wet rock to devour it, leaving behind guts and bones. After eating about 20, he