Earlier this year we shared rare video out of Yellowstone National Park of a grizzly bear taking down a young but good-sized bison in broad daylight. On the other side of the summer season on the Yellowstone Plateau, another park visitor was recently able to catch equally dramatic footage of a grizzly killing a bull elk.

The incident took place on September 18 and was captured on camera by B.E. Judson, who quickly uploaded the video to YouTube. Her accompanying description explains the predation event took place a little past daybreak along the Yellowstone River where it meanders its way north out of the Hayden Valley, one of the premier wildlife-watching hotspots in the park.

The grizzly chases the elk down the riverbank and out into the flow. Just as the bear reaches him, the bull wheels around to confront his pursuer with a formidable rack of antlers. To no avail, however. The grizzly – a huge, almost black male (or boar) – efficiently sidesteps those spear-points and grabs the elk on the back, clawing and tearing in with his teeth.

The elk soon loses balance in deeper water and begins rolling and flailing in the river as the grizzly presses his attack. Eventually, the bull appears to drown and go motionless, upon which the bear continues his high-exertion labour by shoving and tugging the carcass ashore.

“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 the Hayden Valley,” Judson wrote.

Tough as it is to watch the elk’s demise, its meat is a welcome boon for the grizzly: bears are currently packing on as many pounds as possible – a period of around-the-clock fall foraging known as “hyperphagia” – to prepare for their extended winter sleep just around the corner.

The bear enjoying his spoils.

As with the Yellowstone grizzly killing the bison back in May, it’s unusual to see an attack such as this play out – let alone in full view of a major park road. That said, this brand of predation certainly happens.

This time of year, elk are embroiled in the breeding season. It's during the rut that mature bulls are variously trying to corral cows into harems, get their romance on, and meanwhile exert dominance over rival bulls through bugling, strutting, chasing, and occasional locked-antler clashes. This makes the bulls, for all their size, swagger, and weaponry, especially vulnerable to predators. For one thing, they’re quite distracted and hormone-crazed, not as wary as they are the rest of the year. For another, the rigours of the rut see their physical condition – prime at the start of breeding season – decline over its intense weeks, and occasionally manifest as outright bodily injury from fighting, all of which leaves them less capable of outrunning or defending themselves against large carnivores such as grey wolves – and grizzlies.

Read more: Eerie footage of elk bulls brawling at night to a soundtrack of clattering antlers and high-pitched bugling

Indeed, Judson told MeatEater that the bull elk killed by this grizzly appeared to have “a puncture wound on its left flank,” quite possibly from a rut battle – which may have impaired it getting away from the bear.

For the above reasons, fall is one of the main seasons when grizzlies find decent success preying on full-grown elk. Another may be early spring, when winter-weakened elk may flounder in Yellowstone’s long-lingering snowpack while hungry bears, freshly emerged from winter dens, can – with their lesser “foot-loading” – run more easily over it. Grizzlies also get a lot of scavenging done in spring, given the inevitable toll winter takes on a good number of elk, bison, and other ungulates.

Otherwise, the prime elk-hunting window for grizzlies tends to be late spring and early summer, when young elk calves lack the speed and endurance to outpace the bears. Grizzlies will search sagebrush and grassy swards for newborn calves – which spend their first few weeks mostly motionless in prone hiding – and, later, will charge at elk herds to run down the fast-tiring youngsters.

Elk are a significant part of a typical Yellowstone grizzly’s omnivorous diet, though much of that venison is ingested as carrion. Scavenging grizzlies have enjoyed particularly rich pickings since wolves – which actively hunt elk year-round – were reintroduced to Yellowstone National Park in the mid-1990s. The sheer abundance of large ungulates in Yellowstone appears to be one reason why grizzlies here are more carnivorous than many other populations of brown bear.

The takedown of the bull elk by the dark boar – which has been identified as one known to biologists, No. 791, roughly nine years old – is a demonstration of the grizzly’s prowess as an occasional hunter of large game. But the days following the kill, which remains highly visible on the riverbank, have given many tourists an up-close look at the behaviour of grizzlies around carcasses such as this.

In typical fashion, the grizzly quickly covered some of the dead elk in dirt – a way to thwart scavengers. But the main way grizzlies thwart scavengers is by hanging around – or right on top of – a carcass. After the violence of the predatory act itself, the downright serene photographs and videos taken of the bear snoozing away on his spoils make quite the contrast:

A grizzly stewarding a carcass – whether its own kill or scavenged feast – is, needless to say, not all sweet dreamer, though: it will mount ferocious defence of such a bounty, and few creatures in the world can be so ferocious as a defensive grizzly. A few wolves have swung by the carcass, but have been effectively stymied by its enormous and intolerant minder:

Deby Dixon of Deby’s Wild World Photography, who’s been snapping some dynamic shots of the bear’s feast, told USA Today’s For the Win for an article posted last Wednesday, “Wolves tried to come in yesterday, but this bear won’t even allow ravens to share, which is unusual.”

The big boar’s vigilance around his kill – even if that vigilance periodically takes the form of sacking out on top of the dirt heap – is another reminder to be bear-aware when exploring Yellowstone and other North American grizzly country on foot. Grizzlies aren’t bloodthirsty monsters and are more likely than not to hightail it upon sensing human beings. But a surprised and defensive griz met at close range can respond aggressively indeed, and the two worst-case scenarios are bumping into (a) a sow with cubs or (b) a bear guarding a carcass. (Yellowstone offers a slew of bear-safety tips and guidelines on its website.)

You don’t want to blunder in upon any grizzly on a carcass, let alone one as massive as No. 791. His recent elk feast along the Yellowstone River is providing parkgoers at the world’s oldest national park the opportunity to watch a feeding bruin at a safe distance – and to reflect on the perils a bull elk, large and magnificent a beast as it is, faces during the rough-and-tumble rut.

Top header image: Doug Brown/Flickr