Most of these terns were photographed at various times during the breeding season at Bolsa Chica wetlands in coastal Orange County, California, as they flew between fishing areas and their nests; the bird below was at Honeymoon Island, Florida.   Often it's hard (for me, at least) to tell royal terns from the related elegant terns, especially in flight; royals are a bit larger and have thicker, straighter bills; elegants tend to have more slender and slightly downcurved bills.   But it doesn't seem as clear-cut in nature as in field guides and I'm not 100% sure of the IDs of some of these birds.
            For photo geeks, the pictures were all taken with a heavy but stabilized 500 mm lens, hand-held, at shutter speeds of 1/1600 or 1/2000 second.   Modern photographic technology really works: with the excellent autofocus ability of the lens and camera, almost all the pictures I took were very sharply focused -- but most were in awkward poses, or with wingtips outside the frame, or in bad light (what you see here are the best of many).

Click here for more flight pictures of resting royal terns, Forster's terns, courting elegant terns, least terns, and Caspian terns.

• Canon 1D Mk II, 1D3, or 7D2; 500 mm IS lens or 800 mm IS lens, some with 1.4X converter (2004, 2008, 2017)