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

(last update: December 2015)

Black-tailed Gull (crassirostris) adult April - June

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.

BACK TO PART 1: IDENTIFICATION

BELOW: PART 2 DESCRIPTION

Adult
Upperparts dark slate (Kodak Grey Scale 8-10.5), often with slight brownish tinge. Primaries blackish, in small minority (males) P10 with 1-10mm indistinct mirror in one web only. P8-9 black. P7-4 with black markings near tips, on P4-5 often restricted to one web. P1-4 slightly paler than P5-10 (Kodak Grey Scale 9-11). Primaries with white tips, 1-3mm on P6-10, 5-7mm on P1-5. Secondaries and longest scapulars blackish with 15-20mm white tips. Underside of flight feathers sooty-grey, darkest on primaries. Marginal coverts white. Primary coverts sometimes with black drop markings. Underparts, underwing-coverts, rump and tail white; tail with black subterminal bar (in T1 28-60mm) and 15-20mm white tips; T6 white, sometimes with 13-23mm black subtermirral bar on innerweb (may be reduced to shaft-streak). Outer web white, sometimes slightly greyish-tinged. White eyelids above and below eye. Iris creamy, yellow or greyish-yellow. Orbital ring orange-red to brownish-red. Bill yellow to greenish-yellow with black subterminal bar and vermilion-red gonys-spot and tip. Legs yellow to greenish-yellow.
Adult summer (Feb-Aug/ Sep) Head white. Bill deep yellow with black subterminal bar and dark red tip. Orbital ring black or dark red. From late summer loses white tips to worn primaries and sometimes shows contrast between worn, brownish-tinged saddle (often even some coverts) and dark grey wings.
Adult winter (Sep-Mar) Head white with grey, sooty or grey-brown ear-coverts and hindneck, creating a dark half-hood, most distinct bordering the hind-collar; sometimes as streaks or spots, especially around the eye (emphasising the white eyelids above and below eye). Chin, throat and upper breast often slightly dark-spotted. Bill yellow with greenish or greyish tinge. Has black subterminal bar 8-12mm wide on upper and 13-17mm wide on lower mandible, sometimes covering red gonys-spot. Bill-tip chrome-yellow to ivory, 10-14mm on upper and 6-8mm on lower mandible.

Juvenile
(fledging-Sep/ Oct) Head dark greyish-brown; hindneck, ear-coverts and neck-sides darker blackish-brown, sometimes as dark hind-collar. Forehead, lores, chin and throat paler greyish-brown with indistinct dark spots. Pale eyelids above and below eye narrow but conspicuous. Mantle, scapulars, lesser coverts, median coverts and tertials dark brown with broad sandy to pale brown(with wear whitish) edges, creating scaly pattern. Tertials dark brown with pale edges restricted to distal part; rarely very narrow pale edges reach bases. Greater coverts brown (sometimes slightly paler than median coverts, especially at bases) with narrow but solid pale tips and edges (broadest on inner 50%) and sometimes faint dark subterminal markings. Rump and uppertail-coverts white with broad dark bars, spots or chevrons. Flight feathers sooty-brown, P1-5 and secondaries with narrow pale tips. Breast, flanks and upper belly dark brown, often forming a broad bar across the breast and upper belly. Central to lower belly and vent whitish. Underwing-coverts and axillaries sooty-brown with paler bases; greater primary coverts dark brown or pale with brown tips, often forming a pale ‘double-comma’ as in younger Pomarine Skua. Rarely, pale areas on underwing more extensive, with dark tips only to coverts/axillaries. Undertail-coverts whitish with row of dark chevrons along edges; central feathers white or only slightly dark-spotted. Tail brownish-black with 2-4(5)mm buffish tips and white extreme base. Iris dark brown. Bill pink, orange-yellow or yellow with 18-27mm black tip, usually reaching gonys; sometimes with narrow pale tip to upper mandible. Legs flesh, pink or fleshy-brown.

First-winter
(Sep/Oct-Mar) as juvenile, but head paler and greyer; forehead, lores, chin and throat off-white. Crown and ear-coverts sometimes streaked greyish-brown. White eyelids above and below eye stronger. Hindneck and neck-sides brown, forming dark collar. Mantle and scapulars greyish-brown with dark spots, streaks or subterminal markings, broad sandy edges  and grey bases; scapulars sometimes sandy with dark restricted to shaft-streaks/ bases, creating pale line against darker coverts. Bare parts as juvenile, but pale on bill-tip often broader. Saddle much worn by spring, contrasting clearly with darker wings and hindneck (pers. obs. China, May).
First-summer (Apr-Sep) similar to first-winter, but head generally paler. Mantle / scapulars with grey admixed, often contrasting well with bleached off-white feathers. Rump and uppertail-coverts with finer dark markings. Underparts whitish with greyish-brown shading or patches on flanks and breast-sides, often joining collar. Wing mainly juvenile, but sometimes with a few grey median coverts admixed. Juvenile tail loses pale tips. Iris medium to dark brown, sometimes creamy. Bill pink to pale green with black tip; sometimes narrow red tip to one or both mandibles. Legs pale green, sometimes with a yellow or pinkish tinge.

Second-winter
(Sep—Mar) A mixture between first-winter and adult. Compared to adult, head-markings usually more extensive with coarser brown spotting or shading, sometimes continuing onto breast. Upperparts with slight brownish tinge and some brown wing-coverts (with narrow  dark shaft-streaks and paler tips) admixed, especially median coverts and inner coverts. Tertials brownish-grey with broad pale edges. Tail-bar generally broader (max.70mm on T1), often with slightly dark mottled division between black and white bases; normally including full bar on T6 (see adult). Primaries brownish-tinged with pale tips to P1-5 only, narrower than on adult. Lacks white on P10. Secondaries sometimes with brown subterminal markings. Primary coverts blackish with paler edges; dark most extensive on outer three, where it creates drop-spots. Underparts as adult, but often with slight brown to grey wash on breast-sides and flanks. Iris pale grey to brown. Orbital ring dark. Bill generally duller than in adult: bluish-grey with dull yellow, fleshy or pale green tinge, black subterminal bar and often red tip or gonys-spot (often only as indication); entire tip sometimes black. Legs greyish with dull yellow, greenish or fleshy tinge.
Second-summer (Mar-Sep) similar to adult, but with traces of immaturity such as brown-tinged tertials and darker cutting edges to bill. Wing often more worn than saddle. Legs pale yellow.

Third-winter
Similar to adult, but flight feathers brown-tinged with narrower white primary tips, upperparts with slight brownish tinge, primary coverts with dark drop markings and T6 always black-marked. Bare parts less yellow than in adult.

Aberrants
Leucistic adult known, showing pale grey saddle and almost whitish wing. Bill and legs normally coloured (Doherty & Oddie 2001).

DISTRIBUTION AND MIGRATION

Population <350,000 pairs. Breeds colonially in the Sea of Japan on sandy and rocky shores, sea-cliffs and rocky islets. Coastal; often found in estuaries, bays and harbours. 100,000 pairs Russia (96% in Peter the Great Bay, of which 80,000 on the Furugelma Islands), 150,000 pairs in Japan, where most abundant large gull; otherwise breeds Sakhalin, China, Korea, E Siberia and the Kuril Islands (del Hoyo et al. 1996, Enticott & Tipling 1998).

Post-breeding dispersal to food-rich areas. Russian first-years move to coast of Tatar Strait. Birds from NW Honshu migrate to Pacific coast of Honshu, Hokkaido and S Sea of Okhotsk. Birds from Yellow Sea migrate to S and N along coast. Main wintering range lies in the Korea Straits, Sea of Japan and NE China coast. Small numbers occur further S off the Chinese coast to Hong Kong, where it is a scarce winter visitor.

Vagrant N America (>20, of which five Canada) S to New Jersey and California, E to Newfoundland and Rhode Island; also Kamchatka, Aleutians, Baja California, Philippines, Bougainville and Australia (Victoria) (Higgins & Davies 1996, Mactavish 1998, J. L. King pers. comm.).

MEASUREMENTS

Lengths in mm; weights in g. Own data based on skins in MCZ, MVZ, NRK, UZM. E Siberia, Japan.