I just returned from photographing eagles in Haines Alaska on a ANPW trip. We saw a variety of conditions and hundreds of eagles. The eagles continually flew by and fought over fish creating some great action images. But the challenge was autofocus, especially on birds flying past. I shot a lot of 9 point dynamic autofocus with my D4 with good results. But if you own a D810 or D4s, you better try out group-area auto focus. This mode beat all others in acquiring and focusing on moving birds.
This mode works by activating 5 spots in a diamond pattern inside the viewfinder. Simultaneously all points try to acquire a moving subject, giving you a larger area for acquiring the subject. The results were stunning..eagles flying head on right at you were tack sharp. I’m hopeful other Nikon bodies will use this mode down the road, very useful for the sports or wildlife photographer.