American Herring Gull
Larus smithsonianus
The herring gull is a heavily built large gull with a long powerful bill, full chest and sloping forehead. Males are 60–66 cm (24–26 in) long and weigh 1,050–1,650 g (2.31–3.64 lb). Females are 53–62 cm (21–24 in) long and weigh 600–900 g (1.3–2.0 lb). The wingspan is 120 to 155 cm (47 to 61 in). Among standard measurements, the wing chord is 41.2 to 46.8 cm (16.2 to 18.4 in), the bill is 4.4 to 6.2 cm (1.7 to 2.4 in) and the tarsus is 5.5 to 7.6 cm (2.2 to 3.0 in). Breeding adults have a white head, rump, tail, and underparts and a pale gray back and upperwings. Voice: It has no song but possesses a variety of cries and calls. An initial call in response to a threat is a quick "hahaha", varying in intensity depending on the threat. The more-intense "keow" is a loud yet short alarm call that is both identifying and communicative of impending danger. The "long call" is a series of loud notes during which the head is dipped and then raised.
ID text from Wikipedia, CC BY-SA 4.0

Lesser Black-backed Gull
Larus fuscus
The lesser black-backed gull is smaller than the European herring gull. The taxonomy of the herring gull / lesser black-backed gull complex is complicated; different authorities recognise between two and eight species. This group has a ring species distribution around the Northern Hemisphere. Differences between adjacent forms in this ring are fairly small, but by the time the circuit is completed, the end members, herring gull and lesser black-backed gull, are clearly different species.
ID text from Wikipedia, CC BY-SA 4.0

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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: American Herring Gull and Lesser Black-backed Gull.