It wasn't a bear that made noises last night, at least from what we could tell this morning. Whatever it was that Top O' heard, we didn't see any signs of it trying to get into our food bags.
We're now in grizzly country, though it's unlikely one of those bears would have been the culprit. Black bears live in Wyoming too, and one of them would have been a more likely suspect if our food had been disturbed. A black bear's claws are better suited for climbing trees than a grizzly's.
Grizzly bears kill small animals and feed on the dead carcasses of animals that fail to survive the harsh winter. Later in the spring and summer, they forage on grasses and plants until berries ripen, then they gorge on those. They feed mostly on roots in the fall, as well as army cutworm moths.
Grizzlies are generally wary of humans. Still, they are capable of killing large animals, and that's why people fear them.