Photographing birds in flight is never an easy thing to do. Between trying to keep the bird in focus (or in some cases even getting the bird in focus) and framing the shot it is very difficult. Add to that the fact that you need a decent zoom or prime lens it gets even more difficult. My longest zoom is a 200-400mm but it is too slow for getting useful shots of birds in flight so I am now using my 300mm f/4.0. My guess is that I will go to a 1.4 or 1.7 teleconverter for more reach when I am doing photos like this in the future as you lose some detail when you crop a hawk shot at 300mm.