Black-tailed Gull
Larus crassirostris
The black-tailed gull is medium-sized (46 cm or 18.1 in), with a wingspan of 126–128 cm (49.6–50.4 in). It has yellow legs and a red and black spot at the end of the bill. Males and females have identical plumage and features, although males are larger in size than females. This gull takes four years to reach full adult plumage. As the name suggests, it has a black tail. The bird has a cat-like call, giving it its Japanese name — umineko (海猫, 'sea cat'), and Korean name — gwaeng-yi gull, which means 'cat' gull. In Hachinohe their calls are one of the 100 Soundscapes of Japan.
ID text from Wikipedia, CC BY-SA 4.0
Caspian Gull
Larus cachinnans
It is a large gull at 56–68 cm (22–27 in) long, with a 137 to 155 cm (54 to 61 in) wingspan and a body mass of 680–1,590 g (1.50–3.51 lb). Among standard measurements, the wing chord is 38.5 to 48 cm (15.2 to 18.9 in), the bill is 4.6 to 6.4 cm (1.8 to 2.5 in) and the tarsus is 5.8 to 7.7 cm (2.3 to 3.0 in). The Caspian gull has a long, slender bill, accentuated by the sloping forehead. The legs, wings, and neck are longer than those of the herring gull and yellow-legged gull. The eye is small and often dark, and the legs vary from pale pink to a pale yellowish colour.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Black-tailed Gull and Caspian Gull.