Why Do Bears Rub Their Back against the Trees?

There's no itch as far as the bears' habit of rubbing their back against trees is concerned. In fact, this has been found to be a scent mark, warning others to keep off from the real master of the place.

Many theories tried to explain this habit. Some believed females could do it when they were at the peak of their fertility, while others thought that bears just attempt to cover their backs in sap, employed as insect repellent.

But a new two-year research of grizzlies in British Columbia employing digital cameras to gather information on which bears employed the trees for rubbing and when (the same rub trees can be used for generations, so there's no difficulty in observing this behavior). Satellite equipment also monitored the bears' individual movement.

"The cameras show that adult male bears are the most likely to rub trees, and the satellite telemetry tells us that males move from valley to valley in large loops, marking trees as they go, while looking for breeding females," said author Owen Nevin, ecologist of the University of Cumbria.

"By marking the trees with their scent, the male bears get to know each other better, which could reduce fighting among the bears over female mates. Big male bears can seriously injure or even kill each other when they get into a fight. If one recognizes 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." said Nevin.

Offspring also use the rub trees when a male is attempting to chase them away from their mother (males are known to kill sometimes a female's offspring to force them enter the fertility period, so he can get a chance to fertilize her).

"They can visit the tree two or three times a day, sometimes within an hour of the big males, so it may be that smelling like him makes them safer - related animals smell similar and animals are less aggressive toward relatives," explained Nevin.