Black-tailed Gull (crassirostris) / ウミネコ / 괭이갈매기

(last update: December 2015)

Black-tailed Gull (crassirostris) adult January - March

Description in "Gulls of North America, Europe, and Asia", by Klaus Malling Olsen & Hans Larsson, Princeton University Press.

This is a copy of the chapter on Black-tailed Gull, written by Klaus Malling Olsen. "I" in the text refer to the author. If you find any errors, please let me know at marsmuusse at gmail dot com.

BLACK-TAILED GULL - Larus crassirostris (Vieillot, 1818, Nagasaki, Japan)

PART 1: IDENTIFICATION

Length 46-48cm, wingspan 118-124 cm. Black-tailed Gull is a medium-sized, dark-backed gull of the NW Pacific. It is slightly larger than Common Gull and shows a black tail or tail-bar at all ages. The overall impression, emphasised by its short tail, is of a graceful, small, round-headed ‘large’ gull with long, slender wings. When settled, looks attenuated with rounded head, slender bill, long wings and rather short legs. In flight it moves faster and more buoyantly than larger gulls; it is often very agile in hard winds, performing much gliding on angled wings. In light winds its flight is slightly slower than Common Gull. The dark upperparts and narrow wings often suggest a small Lesser Black-backed Gull or a white-headed Laughing Gull.

Adult
Has blackish-grey upperparts with a black wing-tip (usually lacking mirror on P10), narrow but obvious white tertial-crescents and a white trailing edge to the wing. The tail shows a distinct black bar, only matched by Band-tailed Gull from South America. From below, the blackish primaries and grey secondaries contrast with the white coverts and body. The bill is yellow with a black subterminal bar and bright red tip. The eyes are pale and the orbital ring dark. The legs are yellow. In summer the head is white; in winter the hindneck shows brown streaks, sometimes strong enough to create a neck-bar.

Juvenile
Dark greyish-brown with a paler face, pronounced white eyelids, paler lower belly and pale-scaled upperparts. The wing is dark with mid-brown coverts. It lacks a pale window on the inner primaries. The rump is white with dense dark spots. The tail is all dark. The underwing-coverts are dark brown in contrast to the paler flight feathers. Often shows pale ‘double-comma’ near wing-bend as in younger Pomarine Skua Stercorarius pomarinus. Bill pink with a clear-cut black tip, merging into the pale face. Legs pink.

First-winter
Similar to juvenile, but pale face more obvious, often reaching the dark eyes and ‘extending’ to the pale bill-base. The mantle and scapulars are slate-grey with dark markings (often as shaft-streaks) and paler feather-edges. The brown nape to neck-sides is more contrasting than in juvenile. The lower underbody is pale. Resembles California Gull, but this species lacks conspicuous white eyelids, has darker-patterned underbody, and densely barred rump. Also, California generally has better-marked upperwing, with more conspicuous white bar along tips of greater coverts.

First-summer
Similar to first-winter, but face paler off-white with paler grey wash to crown and ear-coverts. The brown hindneck creates a dark neck-boa, which contrasts with the pale bleached mantle. Has greyish or brownish breast-sides and flanks. Mantle/coverts often strongly bleached (sometimes whitish) through wear, but these parts piebald when new dark feathers occur. Flight feathers brownish through wear. Rump white with indistinct dark spotting. Bill and legs fleshy to pale green, the former with black tip.

Second-winter
Intermediate between adult and first-year. Compared to adult winter it has stronger dark head-markings and traces of a brown breast-bar and flanks. Shows grey saddle and mid-wing bar (median coverts) against brown, dark-patterned lesser and greater coverts; saddle and new coverts often brown-tinged compared to adult. Wing-tip is browner with narrower white primary spots, looking all dark with wear. The broad black tail-bar almost reaches the tail-base, suggesting an all-black tail. The bill is pale grey with a blackish tip. The base may show a yellow or pinkish tinge. Legs dull yellow to fleshy.

Second-summer
Similar to second winter, but head white.

Third-winter
Similar to adult, but with a brown tinge to the primaries (which have narrower white tips), upperparts and secondaries, usually broad dark markings in the tail, duller bill and greyish tinge to the yellow legs.

VOICE

A deep mewing kaoo kaoo, kau-kau or yark-yark-yark. Also a plaintive rasping mewing, higher than in Vega and American Herring Gulls (Higgins & Davies 1996, Sibley 2000).

MOULT

The adult moult to winter plumage is complete June-Oct/Nov. P1 late June, P3-4 late July/ early Aug, P4-7 late Aug, P7-9 mid-late Sep, P10 (late Aug-) mid-Oct-mid-Nov. Tail, secondaries and coverts late July-late Sep, lesser coverts generally last. Body from June, head from mid-Aug, often not finished before late Sep (skins MCZ). Moult to adult summer partial Jan-Mar, including head and body; >95% white-headed by mid-Feb (pers. obs. in Japan).

Moult to first-winter partial late July-Jan, including head, neck, mantle, scapulars, rump, some tertials and sometimes some lesser coverts and inner median coverts. Starts with head, neck and upper breast (Il’icev & Zubakin 1990, King & Carey 2000). Moult to first-summer partial Dec-June, including parts of head.

Moult to second-winter complete late Apr-Oct, thus earlier than in adults, starting with P1 / inner median coverts late Apr. Moult has reached P2-3 late May and P7-9 late Aug. P10 early Sep-mid Oct. Secondaries and tail June/July-Sep/Oct. Head and body july-mid-Aug. Most median coverts renewed around mid Aug, as well as inner greater coverts and lesser coverts. Vagrants to Australia began moult to second-summer Aug-Sep, probably adjusting to austral seasons (Higgins & Davies 1996).

>>> PART 2 DESCRIPTION >>>