Swinging a camera lens around accurately can take practice. Doing it while trying to focus on a fast moving bird takes even more practice.
This tern was shot at Bolsa Chica reserve in Huntington Beach, a very nice tidal marsh that used to be an oil drilling field. There are a couple of things I do to shoot this type of shot:
1 - autofocus is set by the back button only, not the main shutter button
2 - exposure was set manually, and dropped 1/2 stop because of the white
3 - 8 frames per second
I know that some people manually focus this type of shot, my eyes are not that good anymore. I am impressed they can, but I like to live in my limits. If you have a hummingbird feeder, you can practice on them, and get some good shots. But don't cheat by just waiting for them to return to their favorite spot.
ISO 640, 1/2000 f 6.4. Canon 7d 100-400