The grizzly here seems to have a bigger range than the black bear. Bait sites that previously didn't seem to compete for the same bear, started showing grizzly sign at each one. When the bear seemed to be in one corner of the area, the black bears trickled back in.
We covered our baits with natural material, black bear seem almost mannerly in removing the limbs and cover. Grizzly hits look like a grenade went off in the bait pile.
Signs of laying up on the bait until it's gone also appear. Big black bear never seemed to do this.
Most of what I suspect is guess work, I sure wish we had todays camera's, back then.
A couple of youtube video's show a little of the behavior we're talking about.
Bear Killing Bear
Grizzly chasing black bear
Scarface (Grizzly Bear) eats dinner
I keep swearing I'm going to learn posting links, sorry.
Like has been said season, mood, personality all play into it, ask Timothy Treadwell. I can't find it again, but there was a video showing a small sow with cubs, going nose to nose with a big boar on a bison carcass. He's full, tired and leaves it to her. Another day he might eat her and the cubs.