Professional photographer Christopher Martin spends a lot of his time watching wildlife, so when he spotted an elk erratically walking back and forth on a rail bridge in Banff National Park it caught his eye.

"It was unusual behaviour because it was going one way a few steps and then it would double back, and it did that a few times," said Martin, who was driving toward Lake Minnewanka on Sunday morning.

Curious, the Bragg Creek resident pulled his car over and grabbed his camera, which he always keeps handy, to get a better look.

"As I pulled out the camera and the lens, I could see a wolf head appear and grab on — bite the neck — so then, I knew something amazing was going on," he said.

The wolves pursued the elk back and forth along the bridge as it attempted in vain to find an escape. (Christopher Martin)

"I got out of the car and hiked up a hill on the one side right where the railway overpass bridge is, so I could get level with the bridge deck and obviously see much better."

Once he reached the better vantage point and found himself within 150 metres of the elk, he could see there was not just one wolf attacking it, but at least four.

"They were alternating between hemming the elk onto the bridge, to keep it on the bridge ... and then they would alternate in attack," he said.

"So, one or two would attack from the back and then the other one would bite on the neck, or vice versa."

A male wolf, with his face already bloody from an earlier attack on the elk, looks to deliver a fatal blow. (Christopher Martin)

"It seemed liked it was the alpha male or at least a very strong male that was going after the neck and taking that frontal attack, which obviously can be dangerous," Martin added.

The pack took the elk down twice and each time it managed to get back up and continue trying to flee.

Finally, the wolves took it down for a third time, and it didn't get back up.

A male wolf lunges at the elk's neck while three other wolves watch closely from behind. (Christopher Martin)

"It was that powerful male that did a kind of wrestling takedown by twisting on the neck and pulling it down," Martin said.

"It finally stayed down and the pack then jumped on and got into the feast."

Parks Canada employees had arrived by this time and were monitoring the situation, and Martin chatted with them while the wolves ate.

No trains had yet come along but, concerned about the safety of the wolves, officials decided to move in and remove the carcass.

A male wolf focused on a frontal attack, going for the elk's throat, while the rest of the pack distracted the animal by attacking it from behind. (Christopher Martin)

"The elk was not right on the tracks but it was right on that bridge deck, so not a very safe place to leave it," Martin said.

"So, obviously they had to move it. But there was about 40 minutes, 45 minutes where the wolves were able to congregate on that carcass. So I feel like they got a pretty good fill from that."

Two wolves pant heavily after taking down the elk for the final time. (Christopher Martin)

The wolves simply walked away as the humans approached the carcass, he added.

"They were pretty skittish," Martin said. "They were not interested in holding their ground ... all four of them kind of melted into the forest."

Martin has been taking photos professionally for the past 10 years, primarily focusing on wildlife and natural landscapes in the Rocky Mountains and Canadian Prairies.

A wolf peeks its head up above the railway overpass wall with a piece of elk in its mouth. (Christopher Martin)

"It was definitely right place at the right time," he said of his chance encounter with the elk takedown.

"I spend a ton of time where you see no wildlife but it's always in the hopes of something like that," Martin added.

"To be able to see the full cycle of life in the park is pretty amazing."

Martin has more photos and descriptions of the event on his website.