A group of tourists, including several children, have risked their lives at Grand Teton National Park by disturbing a grizzly bear feeding on an elk carcass at the roadside. Bears, like all wild animals, prefer to avoid contact with humans and will usually leave an area first if people are around, but they are fiercely protective of their food sources and may attack if they believe those sources are threatened.
They aren't just protective of their kills, either. Many authorities in the US and Canada close sections of trail and some campsites in late summer and early fall to allow bears to forage for berries in peace.
