Posted by: Tony Carson | 5 September, 2007

Grizzly tree rub secrets revealed

A long and vexing question in my life has finally been answered: Grizzly tree rub secrets revealed.

Some years ago I was on a hike through Kluane National Park in the Yukon when I came across a terrifically strange sight: a tree with a lot of bear hair hanging from it like Spanish moss and leading up to the tree a series of defined imprints in the ground, as if the bears all used exactly the same stride to approach the tree. Why this tree and why the imprints?

Owen Nevin, a behavioural ecologist at Cumbria University, UK, who carried out a study, said: “A handful of trees (‘rub trees’) are used for years by different grizzlies who each approach the trees in exactly the same way.

“They will step into the footprints of other bears that have approached the trees, urinating as they approach.

“Then they rub their back on the tree, turn around and then bite the tree and claw it. Then they give it a ‘bear hug’ by rubbing their chest against it, and then they rub it with their back again.”

Many theories have been put forward as to why grizzlies are rubbing these trees: some thought they were using them to scratch an itch, others that they were trying to rub on tree sap to repel insects, while some thought they were using the trees to attract mates.

Dr Nevin told the BBC News website: “Until now, we haven’t really known which bears use these trees and why they use them.”

“For a large grizzly bear, the only real source of mortality is other big bears, so lots of strategies are adopted to reduce the likelihood of having to fight.

“If one recognises the other from the scent marks on the rub trees in the area, he knows he’s in for a tough fight – he’s on the other guy’s patch so to speak – so it might be better to back away than make a serious challenge.

“When two males meet, the more information they have, the better for both of them.”

Here is another one I’d like answered. I was fishing from a canoe on a medium sized lake in Northern Ontario when suddenly the water boiled fantastically, so dramatically that it must have lifted the canoe two feet. We almost capsized. Obviously it was an enormous air bubble but where did it come from? Still don’t know.

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