By the way, here are some tips for shooting birds in flight:
1. You need a shutter speed of 1,000th for large birds, 1,250th to 1,600th for smaller birds.
2. Shoot in the M setting. Autoexposure is not fast enough for shooting birds in flight and more often then not exposes on the background, not the bird. Furthermore, using autoexposure slows down the autofocus. On a bright day start with 1,000th at f8 at ISO 800. Take a few practice shots and adjust the exposure as needed.
2. Set the AutoFocus to AI Servo and Zone AF.
3. Set the shutter drive mode to High Speed Continuous.
Its not a bad idea to save these settings as one of your Camera User Settings. I use C3 for the above settings.
Also, when shooting bird in flight either set the IS to 2, or turn it off altogether.