The Nikonians Wildlife Photography forum has a vast number of superb images of Birds in Flight (aka "BIF") and you will surely be tempted to try it out. It is a fun challenge to get an image with the subject completely in focus, frozen in the air, and yet with an excellent background. Learn lens recommendations and field-proven settings in this article.
Shooting birds-in-flight is a difficult photographic challenge but when you nail a few shots, it is a most rewarding experience. Starting off, many people try to shoot Birds-in-Flight as a bit of a fun challenge. Once they have a little success, they find themselves drawn into this addictive photographic genre.
All of Nikon’s current cameras are capable of producing good results when shooting birds-in-flight. Advanced cameras offer more settings and easy to access controls, but you can get started with any camera.
One thing that is necessary is the relatively modest investment on a decent telephoto lens. The Nikon 80-400mm f/4.5-5.6 AF-S VR, Nikon 300mm f/4 AF-S and the Sigma XX-500mm zoom lenses are popular lenses with very good image quality at reasonable prices. The new Tamron 150-600mm looks like it will be a contender in that market segment also.
The next step up is usually a 300mm f/2.8 Nikkor with Nikon teleconverters, or the Nikon 200-400mm f/4 VR. The Nikon 300mm f/2.8G AF-S VR is a superb lens and works well with all 3 Nikon teleconverters. Another good option of similar quality is the Sigma 120-300mm f/2.8 OS with the Sigma 1.4 teleconverter giving you a 170-420mm f/4 lens that holds up well against the Nikon 200-400 f/4G AF-S VR.
Beyond those we move up to the big guns, the worthy 400mm, 500mm, 600mm and 800mm Nikkor lenses that cost as much as a used car.