The caribou migration is a veritable feast for grizzly bears — if the bears can catch them. "American Arctic" premieres Wednesday, April 13 at 8/7c on PBS. [VID: Grizzly bears chasing a herd of caribou. Transcript: Away from the water, the caribou start to relax. It's a mistake. Caribou may be faster than bears on the open plain, but they must also rest the calves. Grizzlies and polar bears are almost the same species and increasingly overlap and interbreed, but grizzlies are a more serious thre