An amateur videographer has captured rare footage of northern resident orcas rubbing themselves at a beach in B.C.'s Discovery Islands near Campbell River.

The Orca Network posted Chris Wilton's YouTube video seen here to its Facebook page.

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In the video, at least four orcas can been seen circling the beach and taking turns rubbing themselves on the smooth, small stones.

"Holy, moley," says one of the amateur whale watchers as an orca manoeuvres in close just metres away and rubs itself along the bottom. "This is crazy...probably feels like a nice massage."

"Powerful," says another as the snuffling whales noisily blow up a storm. An orca is seen here near shore on a beach in the Discovery Islands near Campbell River. It is one of several orcas captured rubbing themselves on stones in Chris Wilton's amateur video. (Chris Wilton/YouTube) The Orca Network in its Facebook post quoted Jackie Hildering, who runs a blog called ​ "The Marine Detective. "

"Absolutely remarkable footage of northern resident orcas with their culturally unique behaviour of rubbing themselves on beaches like this."

"I happen to be with whale researchers Janie Wray and Christie McMillan, and we believe these whales are the A42 matriline. The big male is very distinct. He is A66 born in 1996."

​Scientists say this behaviour is almost entirely unique to northern resident orca whales and is so uncommon that it's hard to study.

They aren't sure why the northern resident whales exhibit this behaviour, although some have theorized it's a learned habit passed down from one generation to the next.

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