The only bird I have seen dive faster was a Peregrine Falcon. And really once you hit these speeds who cares.
These images should be viewed on a full screen, full size. I caught this Tern diving straight down into a marsh and followed him with my longest lens. They hover, then plunge like a bullet.
Click, or double tap, to view in the gallery.
The dive ended into the reeds hidden from me. Even so the dive is pretty amazing to see.