On Friday, a tourist in Yellowstone National Park captured some incredible video of a grizzly bear doing what grizzly bears do, especially when they're getting ready to hibernate soon. In the footage, this particular bear seizes on an opportunity and chases a bull elk out into the Yellowstone River. Watch what happens next.

Here's how the person who filmed the encounter described it on their YouTube page:

At first light this morning, I pulled over, noting a Bull Elk with a few cows in the upper right of the meadow depicted in the opening photograph. I was startled moments later by a Bull Elk running into the Yellowstone River pursued by a large Grizzly Bear. The Grizzly was successful in taking down the Bull Elk after only a few minutes, but it worked for around a half an hour to redirect it to the far side of the river and secure it on the east bank, about one- hundred yards downstream from the north end of Hayden Valley.

Grizzly bears usually step up their eating game as the calendar turns to fall. Hibernation begins in late October and can actually start in September, depending on the weather. The bears will eat as much as they can pre-hibernation, according to WildMontana.org, consuming as much as 20,000 calories per day and adding as many as 30 pounds per week.

The bears eat nothing during their hibernation siesta. In a typical year, the males will be the first to emerge from their dens sometime around mid-March. The females with cubs are usually the last to come out sometime in late-April or early-May.