Hydroprogne caspia
Very large tern, with deep, dagger-like, blood-red bill with dark tip. Large, black cap reaching well below the eyes. Grey upperparts and white underparts. Rather short tail. Outer primaries distinctly darker than the rest of upperwing, and outer underwing almost black. Unmistakable from the size alone, and leaves a gull-like impression, lacking the elegance of smaller terns. Immatures with paler bill and white forehead (as in adult winter), and markedly speckled back. Hovers and dives. Often rests on the surface, feeding like a gull.
Easily recognized by its very harsh calls. Sometimes likened to the sound of a plate of steel being dragged across a concrete floor. Similar in harshness to Grey Heron, but more drawn, with an accented middle; "Kraaeeet", or with a double syllable start "ka-ha-kraaaeet". Immature birds begs with a penetrating, sharp whistle.
Wikipedia: map (se also Xeno-canto below)
Birdlife ecology
