Larus marinus
Adults: Black back and pinkish legs. Large white windows at tips of primaries, and broad white trailing edge of wing. A very heavy gull with a heavy bill and broad wings. Juveniles with pale head, boldly spotted back and heavier bill than Lesser Black-backed and Herring Gull.
Can be identified from the low pitch alone. Clearly deeper than Lesser Black-backed and Herring Gull.
Xeno-canto: map
Birdlife ecology
