Terns must be one of the more challenging birds to photograph in flight but I think one of the most rewarding. They generally fly fast, often straight, then change direction dramatically and skillfully. I've also seen them in mid-air disputes with other birds. Yet, if you can get a good shot, they're elegant and beautiful.
I took this shot a few years ago at RSPB Minsmere, from the platform along the sea front. It was hovering over a channel looking for sand eels. I was lucky enough to have good light and the bird hovering long enough for me to get a burst of shots.