Wounding a bear, and leaving it to come upon some other poor guy in the woods is a very very bad idea. A wounded animal, especially a predator, will even attack people it would not have if its in pain. That's just crazy advice. Not to mention, bird shot has a hard time stopping a man sometimes. It is ridiculous for bear defense. I have personally seen a bear take two 300 win mag rounds-well placed, to stop it. A buddy of mine killed a big bear with three rounds of 30-06, and he was crapping his pants thinking it was not going to go down before it got to him. Hell, I have hunted birds that were not killed with shot and had to be killed by hand once found in the brush.
I don't mean any offence to you at all, its just that the old forestry professor doesn't know anything if that's what he told you. Many fishing guides in Alaska carry a pistol grip 12 gauge with slugs. You have to stop the bear. Break bones, penetrate to vitals, that sort of thing. No one I have ever seen carried bird shot in the bush, except to hunt birds and rabbits, and they always had something else to handle bears.