Of all the wildlife photo trips that I've been on, I think this lens would probably work best for bears in Alaska. You don't need a lot of reach, since you're often nice and close to the bears and they also happen to be rather large . The f/2.8 would be really nice for low light at dawn and dusk, plus of course to give a super soft background. But you'd probably still want to have a 70-200 f/2.8 on a second body, for those moments when the bear walks really (really) close. On all the other trips I've done, the 500 f/4 has been my mainstay and I find that it's pretty rare to need anything much wider than that.