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| The Black-tailed Gull (Larus crassirostris) is a fairly common bird in East Asia, with a range centred on China and Japan.The species is migratory with birds being regularly recorded as far south as Hong Kong and vagrants reaching as far south as Australia. Of interest to US birders, Black-tailed Gulls are now recorded almost annually in North America, with most of the records coming from Alaska (mutliple occurrences) and the East Coast. If, as seems likely, they are arriving via a northerly route, they are a potential vagrant at almost any location in the US. There are no European records (yet), but given this species established record for wandering, it wouldn't be a major surprise if one did turn up. They are quite distinctive and armed with some knowledge of the key identification features this is a reasonably straightforward gull to identify. |
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 The image of an adult bird (right) illustrates well the 'jizz' of Black-tailed Gulls. They are a compact, round headed, short-legged gull with wingtips extending well beyond the tail. They have a similar body size to Ring-billed Gulls, but are noticeably longer winged. The dark back and long wings are a bit Laughing Gull-like. In Europe, they should stand out from the noticeably larger Lesser black-backed Gull.
Early literature suggested that Black-tailed Gulls reached adult plumage in their third year, but this is in fact a four-year gull (see Lethaby and Bangma Birding, December 1998). |
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First-winter plumage is essentially brown, and unlike, say Common/ Mew or Ring-billed Gulls, they don't show any trace of the adult grey upperparts colour. In that respect they are aligned with the larger gulls which take four years to reach adult plumage. To describe them as essentially brownish, however, doesn't really do any justice to their subtle markings. The brown colouring extends onto the underparts in a smooth, almost marbled pattern. The tail is black, but the rump is white. In California Gulls, a potential US confusion species, at this age the rump is obviously barred. In Lesser Black-backed Gull, a potential European confusion species, the rump usually has some dark streaking and there is more barring on the outer tail feathers. |
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 This late winter bird is rather worn, but you can still see the dark streaks in the centre of the scapulars. It's worth stressing the pale faced appearance of first-winters. This is chiefly feathering, but it's added to by the mainly pale bill, and stands out well even at longer ranges.
Although the face is whitish, the rest of the head is brownish and the dark mark in front of the eye helps to emphasise the white eye-crescents. The bill is long and parallel sided, though with a distinct angle at the gonys. The tip is blackish, but the rest is a pale fleshy colour. |
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 With the moult into second-winter plumage the underparts become whiter and the mantle, scapulars and some of the coverts become grey. These new grey feathers are clearly darker than the grey upperparts on Mew/ Common, Ring-billed and California Gulls. In fact they are a shade darker than Laughing Gulls and anyway these two species are easily separated by their different bill colour - all dark on Laughing Gull - pale with a dark tip on Black-tailed Gull. |
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The upperparts colour of Black-tailed Gull is fairly close to a Lesser Black-backed Gull of the western race graellsii and at the second winter stage there are some similarities in bare parts coloration. But Black-tailed Gulls are smaller and have a thinner bill. There is a dusky wash to the rear crown and hindneck and the whitish eye-crescents are obvious. The pale part of the bill has started to develop a greenish tone and the iris becomes pale. At close range this bird showed a touch of red at the bill tip, and the merest suggestion of red along the inner edge of the black on the lower mandible. |
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 In flight the short tail is apparent, and partly explains their long winged appearance. The black tail contrasts sharply with the white rump. The tail has a narrow white tip which is often difficult to see. It looks quite different from the tail of a Lesser Black-backed Gull of a similar age. The elongated shape and long-winged appearance stand out clearly.
Third-winter birds are very similar to adults, but the wing coverts often have a brownish tinge. And they lack the white primary tips which adults show in fresh plumage at least. The pale area on the bill is now yellow and there is a bit of red at the tip. The legs are rather bright yellow. |
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The iris is pale yellow and there is a red orbital ring. The adults white primary tips are obvious in fresh plumage, but by mid-summer they are often lost through wear. |
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 The long and strikingly patterned bill still shows up well on flying birds. But of course the black sub-terminal tail band is the most obvious flight feature.
On adults the black tail band only just extends onto the outer tail feathers, and although it has a broad white tip, this can be reduced (or even lost) through wear. The white primary tips are again visible here but note that, unlike some adults, this bird lacks a white mirror on the outermost primary. |
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