We live just 50 crowflight miles from Yellowstone National Park, where bears are a constant in the environment. While they try their best (in both Yellowstone and Glacier) to close trails when bears have been sighted, the National Park Service recommends that hikers carry bear spray. See:

http://www.nps.gov/yell/tours/rangerlife/bearspray.htm

I agree with Eric that the spray is useful mostly as a very-last line of defense, and with Kimberly that knowledge of bear habits and behavior is very useful in avoiding encounters in the first place, which is much to be preferred over dealing with an encounter.

The minimum size bear spray recommended for grizzlies is 9 oz. That's a fairly large canister -- roughly three-quarters of a soda-pop can. Little dog- or person-sized containers simply won't do the job.

The "hotness" of the spray varies, too. It's measured in "Scoville units." Get the hottest available. Expect to pay about $40. Carry it on your belt or pack strap. If you surprise a bear you may have only a few seconds (if that) to get the spray out and discharge it. I've heard you should only spray if you're DEFINITELY being charged and the bear is within 30 feet (less if you can stand it); many charges are bluffs.

If you're in real danger, with a very aggressive bear very close to you, you can't afford to worry about whether you're up- or down-wind; if you've surprised the grizzly you're most likely downwind and are going to get some mist in your face. If you do, you'll be in absolute agony for 45 minutes or more, but the bear will get the full force of the liquid, which will be much more potent; you should recover before the bear does. If I'm ever in that situation, I'll go ahead and shoot -- at least it will reduce my chance of being mauled and unless I claw my own eyes out or something, I won't be permanently injured.

MORE ON PREVENTION

The conventional wisdom here in grizzly country is that the human voice is the best tool for alerting bears IN ADVANCE to your presence, giving them time to move out of your vicinity, which most of them will do eagerly, and thereby avoiding an encounter in the first place. Sing, holler, yodel, ululate (like Xena), or make any other LOUD, uniquely human sound at frequent intervals when you're hiking in bear country. Double the frequency in thick timber, around running water, or when it's windy because those factors make you harder for the bear to hear.

Of course warning the bears that you're around also warns everything else. If you're hiking in order to see wildlife you'll be reluctant to make much noise. This is a dilemma I face every time I hike.

ABOUT BEAR BELLS

Out here we generally snicker at people (99% non-local tourists) who put little jingle bells on their hiking staffs, thinking that doing so will repel bears. Jingle bells can't be heard more than a few dozen feet away! Try it sometime in thick timber! Kathy and I hiked in Glacier in '78 with a big clanking cow-bell and while I think it would probably have been pretty effective it was so annoying that we wound up muffling it sometimes. Probably the worst times.

Since moving to Montana five years ago, I've seen one young black bear in the woods (a forest service campground, really) and one sow grizzly with cub in a remote meadow. (Plus a few black bears seen from the car, which I don't count.) In both cases I was (foolishly) making NO noise. I feel lucky that the grizzly encounter didn't turn out worse. We were downwind, so the sow didn't smell us, and we were just coming up on a rise in the trail so she didn't see us. But it was as close an encounter as I'd want to have. We turned and walked briskly in the opposite direction after allowing 30 seconds for a stealthy peek through the binoculars.

Anyway -- do be careful in bear country! Focus on avoiding encounters, rather than fighting/ spraying/ shooting your way out of them. And work on that yodel!

-Mark