Slaty-backed Gull (schistisagus) / オオセグロカモメ / 큰재갈매기

(last update: December 2015)

Slaty-backed Gull (schistisagus) adult April

VOICE
Similar to Siberian Glaucous-winged Gull: deep, hoarse series and an eager haphap. Long-call
lower and slower than in Western Gull (Sibley 2000).

MOULT
Adult moult to winter plumage from May; up to P4 renewed July, P5-P7 late Aug, P9-P10 (late Sep) Oct-Nov. Head sometimes from July; most still have summer head early Sep. Coverts and tail Aug-Sep. Moult to adult summer partial (Jan)Feb-Mar, including head and body. In Japan mid-Feb small minority white-headed (pers. obs.).
Juvenile moult to first-winter Oct-Feb. Moult limited to parts of mantle and scapulars, and probably a few head and body feathers. May occasionally renew a few wing-coverts and inner tertials. Moult to second-winter complete, starting with P1, mantle and scapulars late May-Jun. P5-P7, tail, secondaries and coverts Aug, P9-P10 late Sep-Oct (Cornier & Savard 1994a & b, pers. obs.).
Moult to third-winter similar to adult, but slightly earlier; P6-P8 Aug.

DESCRIPTION
Adult Mantle, scapulars, back and upperwing blackish-grey to dark slate (Kodak Grey Scale (10)11-l2(l4)), generally slightly darker than Lesser Black-backed Gull race graellsii and with more bluish tinge. Primaries with black outer webs and dark grey inner webs. P10 with 30-60mm white mirror, normally separated from tip by dark subterminal bar; 6% show fully white tip (pers. obs. in Japan). P9 dark grey, darkening to black towards tip, in 78% with 20-40mm white mirror, normally restricted to inner web. P8 dark grey with paler inner web: 52% show white tongue near tip, connecting with white tongues on P5-P7. P7-P5 dark grey with pale inner webs and 10-35mm white tongues before black subterminal spot behind white tip. P5 with narrow black subterminal spot, sometimes restricted to one web. P4 rarely with slight dark subterminal spot. P1-P8 with pale inner webs. Primaries and secondaries with 15-25mm white tips, covering 15-20% of width of inner wing. Underside of primaries silver with blacker tips to P5-P10 and white ‘string of pearls’, created by white tongues mentioned above. Underbody, axillaries and underwing-coverts white. Iris creamy, yellow to brownish-yellow, in 30% dark-freckled (sometimes enough to create darkish-looking eyes). Orbital ring purple to purplish-pink, in small minority red. Gape fleshy-pink. Bill yellow with red to orange gonys-spot and paler tip. Base of upper mandible often slightly pinkish-tinged. Legs pink to rosy, rear tarsus often with purplish tinge.
Adult summer (Jan-Aug) Head white. Bill deep yellow with red gonys-spot.
Adult winter (Sep-Feb / Mar) Head to breast-sides with greyish-brown to warm brown spots or streaks. Markings strongest around eyes, where often forming elongated dark patch, narrowing before and behind eyes, but sometimes continuing as narrow line across hindneck. Often reaches upper breast. Bill duller than in summer, in most with pinkish tinge at basal parts; sometimes base greenish-tinged. Some 25-30% show narrow dark markings especially on upper mandible. Legs raspberry-pink, rosy or deep pink, more rarely fleshy; in Japan (Feb 2001) 65% showed raspberry legs, 30% deep pink and 5% fleshy legs (pers. obs.).
Juvenile (fledging-Nov / Feb) Most variable. Head and underbody greyish-brown to dark brown with diluted dark streaks on head and longer streaks on neck to breast; belly often paler with more distinct brown bars. Hindneck and sides of neck paler; often contrast with uniform dark upper mantle. Lores and ear-coverts often uniform dark, forming eye-mask. Mantle and scapulars dark brown to greyish-brown with darker subterminal crescents and pale fringes or notches. Tertials dark to mid-brown (often intermediate in colour between primaries and mantle, thus paler than primaries) with pale fringes, often waved or mottled at tips and sometimes darker subterminal markings; bases often solid dark. Upperwing-coverts pale brown with indistinct darker vermiculations near pale tips, greater coverts dark brown with indistinct pale mottling, strongest near tips of inner 30%, and often solid dark bases. Some 10% with stronger pale tinge or bars on all coverts or paler bases to especially outer greater coverts (as in Glaucous-winged), in flight contrasting with dark secondaries. Primary coverts darker brown with pale fringes. Rump brownish with indistinct pale barring or mottling, dark and pale bars often of even width. Primaries dark brown to brown with varying, often prominent Vs at tips. P9-P10 uniform, P5-P8 with paler inner webs to near tip and narrow pale fringes; may show slight white tongues as indication of adult wing-tip pattern. P1-P4 paler with dark subterminal markings at tips. Secondaries blackish-brown to mid-brown with paler inner webs and rusty tinge to outer web. Underwing-coverts brown in strong contrast to paler flight feathers. Undertail-coverts white with scattered dark spots or waving. Tail blackish to blackish-brown with narrow pale fringes and tips, and pale vermiculations on inner 50%. T6 dark or with inconspicuous pale mottling on outer web and pale base; sometimes pale mottling near bases of T4-T5. Iris dark. Bill black, sometimes with pale tip to upper mandible. Legs pink.
First-winter (Nov – Apr / May) similar to juvenile, but mantle and scapulars intermixed with grey to pale brown with paler fringes and narrow dark subterminal markings (often anchor-shaped, but sometimes as dark triangles; but regularly restricted to black shaft-streaks). Head generally paler especially on chin/ throat, hind-neck and rear ear-coverts; may show dark ear-spot. May appear hooded. Sometimes with slight brown breast-streaks. Coverts, rump, flight feathers and tail bleach strongly from midwinter, sometimes Nov, when P1-P5 become paler with more obvious dark subterminal markings. Tertial centres may then appear darker than
primaries. Legs fleshy to pink, sometimes with darker upper tarsus.
First-summer (Apr-Sep) as first-winter, but coverts (especially greater coverts) and rump fade  to whitish; flight feathers and tail bleach to brown. New upperpart feathers dark, creating piebald pattern. Bill often acquires pale base / tip and eye becomes paler.
Second-winter (Aug-Mar) Head and underparts whitish with irregular dark markings, especially around eye, on rear ear-coverts and weak dark streaks on hindneck, sides of neck and breast. Underbody whiter with more contrasting dark markings on especially breast and flanks (sometimes mid-belly). Mantle and scapulars mud-brown to brownish-slate, often with dark shaft-streaks, indistinct paler subterminal areas and pale edges. From late winter with adult-type slaty feathers intermixed, sometimes on most of mantle/scapulars and some inner median coverts. Upperwing-coverts plain greyish-brown with pale edges, often strikingly pale from midwinter. Lesser coverts darker with broad pale edges and sometimes dark shaft-streaks. Greater coverts mud-brown, sometimes with narrow and washed-out pale bars. Tertials mid-brown with broad pale tips and edges; division between pale tip and dark base varies from slightly dark-mottled to 2-3 bars near tip. P6-P10 and tail much as first-winter, but P1-P5 paler, creating pale window blending into paler bases of P6-P8 (P9). Primaries blackish-brown with broader pale edges than in first-years. Secondaries mid-brown to blackish-brown with paler tips and edges. Tail usually with broader pale base and more obvious dark barring or mottling, especially at T3-T6. T6 white with black subterminal markings or greyish tinge. Tail rarely blackish. Rump white, sometimes with very faint brown bars, contrasting strongly with tail. Under lesser and median coverts dark brown, greater coverts and axillaries often whitish, in contrast to silvery-brown flight feathers, creating three-toned look. In birds with narrow dark feather-edges on coverts, underwing appears pale with line of dark rows. Bill pale fleshy to greyish-yellow with 15-18mm dark subterminal bar and extensive pale tip, generally broadest on lower mandible; division from palebase often Z-shaped. Iris mid- to pale brown, sometimes yellow. Legs pink to raspberry-pink, more rarely greyish-flesh.
Second-summer (Mar-Sep) Head, underparts and rump white, breast and upper belly sometimes mottled darker. Mantle and scapulars dark slate, contrasting strongly with worn, almost whitish wing-coverts (especially greater coverts). Inner secondaries dark. Rest of flight feathers and tail faded and brownish. Bill yellowish with dark subterminal markings and, rarely, red gonys.
Third-winter (Sep-Mar) similar to adult, but wing-coverts a mixture of slate and brown; lesser coverts sometimes paler with darker mottling, greater coverts rather uniform dark brown. Primaries with narrower pale tips, often restricted to P1-P6. Lacks or shows small white mirror on P10 (max. 30mm); sometimes also on P9. White ‘moons’ and division between grey, white and black less distinct. White tips to secondaries often narrower. Underwing similar to second-winter, but dark normally reduced. Tail white with irregular dark markings forming weak, often incomplete dark tail-bar. Bill much as adult, but normally with broad dark subterminal markings, especially on lower mandible.
Third-summer (Mar-Sep) similar to third-winter, but bill often as adult.
Fourth-winter as adult, but primary coverts often with dark shaft-streaks and bill with more complete dark markings on both mandibles, sometimes creating black ring before ivory tip.

Hybrids
Hybrid Slaty-backed x Vega Gull known from Koriak, Kamchatka and Japan (Haffer 1982, J.L. King in litt.). Adults have paler upperparts than Slaty-backed Gull; further details required. For hybridisation with Glaucous-winged Gull, see that species.

GEOGRAPHICAL VARIATION
Very small. Northern population tends to be larger and possibly have darker adult upperparts than southern (King & Carey 1999); further details required.

DISTRIBUTION & MIGRATION
Population 100,000 pairs. Breeds on (top of) low sea-cliffs, on rocky islands and along sandy shores: also inshore coastal waters. In Kamchatka 47,000-111,000 pairs in >200 colonies, the largest Ptichem Island, NE Kamchatka. Hokkaido population small, but increasing. Sedentary with some dispersing into Bering Sea, Sea of Japan and, much more rarely, S to coast of China and Taiwan. In Hokkaido, Japan, the most abundant gull in winter with numbers in icy winters reaching 10,000-15,000 in largest fishing ports (pers. obs., Feb 2001). Non-breeding and winter birds scarce but regular in W Alaska. Small numbers summer Pribilof Islands (max. 8 St. Paul June 1988); vagrant N North America, mainly between S Alaska and Oregon; scattered records from Ontario, Quebec, Missouri, Texas and Hawaii (Zimmermann & Jones 1991, del Hoyo et al. 1996, King & Carey 1999).

MEASUREMENTS
Lengths in mm; weights in g. Own
data based on skins in MCZ, l\/[VZ, NHM, NRK, UZM.
Kamchatka, Kuriles, Amur,]apan and Alaska.
WING
Adult male 426-479 (453.2) 21
Adult female 406-457 (435.1) 17
juv./first-winter 400-447 (431.7) 9
Note Il’icev Cf Zubakiu (1990) glvefor adult male 408-467
(438, u=46), adult female 391-455 (417, u=31).
BILL
Adult male 51.4-64.6 (57.8) 21
Adult female 48.4-61.1 (53.0) 20
juv./first-winter 48.2-58.3 (53.6) 9
Note Il ’icev if Zubakin (1990) givefor adult male 53. 7-64.1
(62.0, n=46), adult female 48.0-59.4 (53.8, u=31).

WING
Adult male 426-479 (453.2) 21
Adult female 406-457 (435.1) 17
juv./first-winter 400-447 (431.7) 9
Note Il ’icev ff Zubakiu (1990) givefar adult male 408-467
(438, u=46), adult female 391-455 (417, u=31).
BILL
Adult male 51.4-64.6 (57.8) 21
Adult female 48.4-61.1 (53.0) 20
juv./first-winter 48.2-58.3 (53.6) 9
Note Il’icev Cf Zubakiu (1990) gtvefor adult male 53. 7-64.1
(62.0, u=46), adult female 48.0-59.4 (53.8, u=31).

BILL DEPTH AT GONYS
Adult male 19.3-23.7 (20.9) 21
Adult female 17.2-22.0 (18.9) 19
juv./f1rst—wmter 16.6-20.7 (18.5) 9
BILL DEPTH AT BASE OF BILL
Adult male 19.0-24.3 (21.7) 21
Adult female 17.5-21.8 (19.3) 19
juv./f1rst—winter 17.7-21.0 (19.2) 9
GONYS LENGTH
Adult male 13.3-18.9 (15.9) 21
Adult female 12.5-16.5 (14.9) 20
Juv./flrst—winter 11.2-15.9 (14.5) 9
TARSUS
Adult male 66.9-75.8 (69.9) 21
Adult female 60.5-68.6 (64.3) 20
Juv./f1rst—wir1ter 60.5-71.3 (66.7) 9
Note Il’icev if Zubakin (1990) givefor adult male 64.6-86.0
(73. 9, n=46), adult female 59.8-78.9 (67.7, n=31).
Weight Average 1,350 (Sibley 2000).

BILL DEPTH AT GONYS
Adult male 19.3-23.7 (20.9) 21
Adult female 17.2-22.0 (18.9) 19
juv./first-winter 16.6-20.7 (18.5) 9
BILL DEPTH AT BASE OF BILL
Adult male 19.0-24.3 (21.7) 21
Adult female 17.5-21.8 (19.3) 19
Juv./f1rst—winter 17.7-21.0 (19.2) 9
GONYS LENGTH
Adult male 13.3-18.9 (15.9) 21
Adult female 12.5-16.5 (14.9) 20
juv./first-winter 11.2-15.9 (14.5) 9
TARSUS
Adult male 66.9-75.8 (69.9) 21
Adult female 60.5-68.6 (64.3) 20
juv./first-winter 60.5-71.3 (66.7) 9
Note Il’icev C? Zubakin (1990) givefmt adult male 64.6-86.0
(73.9, n=46), adult female 59. 8-78.9 (67. 7, n=31).
Weight Average 1,350 (Sibley 2000).

BILL DEPTH AT GONYS
Adult male 19.3-23.7 (20.9) 21
Adult; female 17.2-22.0 (18.9) 19
juv./first-winter 16.6-20.7 (18.5) 9
BILL DEPTH AT BASE OF BILL
Adult male 19.0-24.3 (21.7) 21
Adult female 17.5-21.8 (19.3) 19
juv./first—winter 17.7-21.0 (19.2) 9
GONYS LENGTH
Adult male 13.3-18.9 (15.9) 21
Adult female 12.5-16.5 (14.9) 20
juv. /first-winter 1 1.2-15.9 (14.5) 9
TARSUS
Adult male 66.9-75.8 (69.9) 21
Adult female 60.5-68.6 (64.3) 20
juv./first-winter 60.5-71.3 (66.7) 9
Note Il’icev if Zubakin (1 990) givefm adult male 64.6-86.0
( 73. 9, n=46), adult female 59. 8-78.9 (67. 7, n=31).
Weight Average 1,350 (Sibley 2000).

PLATE 48. SLATY-BACKED GULL Larus schistisagus
Large dark-backed gull of East Asia, reaching Alaska yearly; in North America otherwise vagrant. Winters E Asia to Japan. Coastal, occurring in large flocks where food available, such as fishing ports and dumps. A compact, rather short-legged gull with strong bill and small beady eyes situated centrally but high in head.
1. Juvenile (Aug-Nov) Head and body greyish-brown, often lacking any strong barring. Mantle and scapulars mid-brown with pale notchings. Coverts and tertials with diffuse pale patterning compared to Vega Gull, on greater coverts barring mainly on inner coverts and along edges. Primaries dark, varying from dark brown to black, often with broader pale tips and edges than in Vega Gull. Bill black.
2. First-winter (Sep-Apr) Generally greyish-brown with diluted covert pattern. Mantle and scapulars grey with dark shaft-streaks or subterminal markings, appearing much weaker and unbarred compared to Vega Gull. Head paler than in juvenile through wear. Bill starts to develop fleshy base.
3. First-summer (or pale first-winter) Some appear very pale with much-bleached coverts already from midwinter. Primaries and tail bleach to brown. Similar to Glaucous-winged Gull, but less ‘evil-looking’, with better-marked mantle and scapulars.
4. Second-winter (Aug-Apr) Retarded birds similar to first-winter, but bill paler-based, eye
Bicoloured, tertials and greater coverts with finer pale vermiculations, and primaries darker with broader white tips.
5. Second-winter (Aug-Apr) Slaty-grey saddle often in very good contrast to pale-patterned wing-coverts, which soon fade to whitish.
6. Third-winter (Aug-Apr) Similar to adult, but with scattered brown, pale-marked coverts, narrower black subterminal bill-markings and narrower white wing-tips.
7. Adult winter (Sep-Mar) Adult shows s1aty-grey upperparts with broad white tertial edges melting into white secondary tips. Legs fleshy to rosy or raspberry-pink. Head dark-streaked or -spotted, often with denser dark streaking around and behind eye, creating dark streak through eye. Eyes pale, often as pale as in Herring Gull. Bill often with narrow dark markings on upper mandible.
8. Adult summer (Feb/ Mar - Sep) Head white. Slaty-grey upperparts often slightly bluish-tinged. Legs deep pink or raspberry-pink. Orbital ring pinkish-red.

PLATE 49.
In flight rather short-winged with full body; appears bull-necked. Outer wing sometimes narrowish-looking.
1. Juvenile (Aug-Nov) Rather uniform greyish-brown. Shows pale window on inner primaries merging into gradually increasing amount of dark on outer primaries; wing panel thus more diffuse, but broader than in Vega Gull and American Herring Gull; often shows indication of adult ‘string of pearls’ on wing-tip. Tail all dark in some contrast to muddy dark-spotted rump.
2. First-winter (Sep-Apr) Underwing contrasting: coverts muddy-brown, contrasting with paler flight feathers; shows dark trailing edge and indication of string of pearls on wing-tip. Breast and flanks often contrast with paler belly and undertail-coverts (not shown here).
3. First-winter (Sep-Apr) Wing soon appears bleached, often with very weakly patterned, pale greater coverts, creating pale midwing-bar. First-winter saddle grey with dark streaks or feather-centres.
4. Second-winter (Aug-Apr) Slaty-grey saddle contrasts well with pale, often diffusely patterned upperwing. Pale pattern on outer wing stronger than in first—years with pale inner webs on primaries almost reaching trailing edge to wing. Rump white in strong contrast to still dark-looking tail. Underwing contrast often very strong with dark coverts, pale silvery flight feather bases and dark trailing edge to hand.
5. Third-winter (Aug-Apr) Saddle still contrasts somewhat to paler-patterned upperwing. Outer primaries grey with dark outer webs and tips; shows white window to P10 and indication of ‘string of pearls’ of adult. Tail still with broad dark markings.
6. Adult winter (Sep-Mar) Adult shows slaty-grey, bluish-tinged upperwing with broad white trailing edge ‘melting’ into white ‘string of pearls’ on outer primaries, reaching P8, and connecting with white mirrors on P9-P10. The ‘string of pearls’ shown here is sometimes less complete, as P8 frequently lacks white markings. Head heavily dark-streaked or spotted in winter.
7. Adult summer (Feb/ Mar - Sep) Head white in summer. Note characteristic wing-tip pattern, often strong when seen from below. Underside of flight feathers s1aty-grey, contrasting with both white coverts, broad white trailing edge (which blends into white ‘string of pearls’ onto P8) and black pattern on wing-tip.