Watch: 'One in a lifetime' - Yellowstone tourists witness wolves gang up on grizzly bear

A group of tourists have witnessed a scene straight out of a Sir David Attenborough documentary, when a pack of wild wolves decided to take on a giant grizzly bear.

In a stunning video shot by Tied to Nature tour operator Adam Brubaker, tourists witnessed a pack of 10 wolves surround a bear which Mr Brubaker believes was eyeing off their kill.

The encounter, which happened at Hayden Valley in the famed Yellowstone National Park, was described as a "once in a lifetime" sighting by the qualified naturalist.

"I had the awesome opportunity to share this once in a lifetime wolf and grizzly sighting while on tour in Yellowstone today." he wrote on his Facebook page alongside the video.

"This grizzly was foraging in the far end of the valley when the wolves started to cross his path. The grizzly started standing up on his hind legs to get a better view of what was going on and then started to approach the wolves.

The wolves start moving in on the giant grizzly bear. Photo / Tied to Nature

"Soon the rest of the wolf pack appears and escorts the bear into the trees."
Some thought that the wolves might have been trying to protect their cubs, but Mr Brubaker believes they had dinner nearby – and didn't want a hungry bear to snack on any leftovers.

"From what I could see the pups were not with them," he told USA Today.

"The white wolf has blood on her face and neck, so there could have been a carcass, but while I watched them they were not feeding on one."

The bear got surrounded by the pack of wolves, which was witnessed in a 'once in a lifetime' event by tourists. Photo / Tied By Nature

While grizzlies and wolves typically avoid each other, encounters have happened before.

"Bears may benefit from the presence of wolves by taking carcasses that wolves have killed, making carcasses more available to bears throughout the year," National Park Service told Newsweek .

"If a bear wants a wolf-killed animal, the wolves will try to defend it; wolves usually fail to chase the bear away, although female grizzlies with cubs are seldom successful in taking a wolf kill."

"I could see that the two species were probably going to cross paths but I did not expect what was going to happen.

"For many people, this would be a once-in-a-lifetime encounter. Neither the wolves nor bears were injured. I believe I saw the same bear yesterday out in the same place this time with no wolves around.

"I have been a guide in Yellowstone for seven years and visiting the park for 20 and every day can offer something new or different."