Royal Tern 2 (I.D. courtesy of Peter May)
When these birds are feeding, they'll fly across the water, relatively high, looking for fish near the water's surface. Once they spot something, they'll briefly hover, and then dive down extremely quickly into the water, and promptly take off again. I tried to follow them as they made their descent, but this was hard to do. This shot is the best I could come up with. Canon 100-400 at 400mm, ISO 200, f/5.6 and 1/500 second (hand-held).