Stay on track
Tracking fast-moving birds with a long lens takes a bit of practice. The trick is to pick a single bird and start tracking it when it’s still quite small in the viewfinder – again much like a missile-guidance system! If you keep your active AF point(s) over your subject, and your thumb pressed down on the rear AF button, your Nikon will adjust the focus as the bird gets bigger in the frame. It also helps to set a cluster of AF points, rather than a single AF point, as this will ensure focus is maintained even if your subject strays away from your selected AF point (again, see your Nikon’s manual for how to set this).