I hardly shoot wildlife, but I've bookmarked Moose Peterson's Website for FAQs on wildlife photography. As Dave says, he too shoots with a fast 400f2.8 and a 600f4 with teleconverters. Plus he says a fast motor drive is necessary. And he looks like a BIG guy.
On the other extreme is is this nut case Timothy Treadwell who shot grizzlies with like a 50 mm lens! He got eaten for his efforts and was imortalized in the indie movie