Moths make up a very large portion of Yellowstone bears' diets. In fact, they can eat up to 20,000 calories worth of moths in a single day.
Each summer, moths will fly into tall mountain slides, where they burrow away to hide from sunlight. It's at this time that grizzly bears and black bears gather as well. They climb high above the timberline and dig through the slide rock to find and eat as many moths as they can. Some researchers estimate that about 40,000 moths are dug up and eaten per day.
A researcher by the name of Hillary Robison spent several summers in the mountains around Yellowstone National Park, observing the bears and she has stated that, "It's kind of like a salmon stream. We've seen bears feeding within several hundred yards of each other and they seem to tolerate each other."
Info and Image Source: Yellowstone Park