My avatar to the left was shot with the 80-400. I don't shoot a lot of birds in flight, but when I do that's the lens I use. One thing you should do is shoot with the sun behind you, to get good light on the bird and good detail. Second, pre-focus the lens on something on the ground about the same distance as the bird, to limit focus hunting. Third, use the focus limiter on the lens. This lens has a bit of a learning curve, but after you get used to the way it acts, it becomes easier to get good shots.