If you saw my recent nature photography video, you'll recognize this shot. It's a Common Tern with a nice fish catch from Nickerson Beach in Long Island. I just wanted to spend a few minutes taking about the technical aspects of this shot.
Birds in flight can be tricky especially with low light conditions around sunrise. The important thing is to use a fast enough shutter speed to freeze the motion of the bird. How fast of a shutter speed really depends on the speed of the bird. As a starting point, I recommend at least 1/1000. To use this fast of a shutter speed, two things need to happen to let enough light into the camera. 1) A wide aperture 2) A high ISO.
Of course with high ISO's you can experience some "noise". I've been using "Neat Image" which is a nice Noise Reduction plugin for Photoshop. Many photographers I know also like Noise Ninja.
For the shot below, my camera settings were: Canon 40D, 400mm lens at f5.6, 1/1000, ISO 400.