Glacier has up to 1,000 bears, both grizzly and black bears. Regardless of bear type, you should always make noise and talk to the bears. Most people will shout, "HEY, BEAR!" as they hike.  You should carry bear spray with you at all times, and if you are also visiting Canada during your trip to Glacier National Park, make sure you bring USEPA-approved bear spray. Otherwise, you might get it confiscated at the border.