Slaty-backed Gull Larus schistisagus Scientific name definitions

55–67 cm; 1050–1695 g; wingspan 132–148 cm. Four-year gull. Breeding adult a typical large, white-headed, dark-mantled gull, with slightly greater sexual size dimorphism than in most gulls; appears stocky with a rounded head and rather short-looking,distinctively bright pink legs (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ). Mantle dark slaty grey, somewhat paler than in L. marinus but darker than in nominate race of L. occidentalis. Wingtip pattern diagnostic ; outer primaries black with white on p9 and p10 or just on p10; the slate-grey on outer primaries is separated from their black tips by series of white spots, beginning at p4 or p5 and extending to p8, producing a ‘string of pearls’ effect. Secondaries with very broad white edge that merges with white tips to pp1–5 in flight. Underwing pattern equally distinctive, appearing tricoloured, the white wing linings contrasting with dark grey remiges and showing same ‘string of pearls’ effect on primaries (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close , 2 Alderfer, J. and Dunn, J.L. eds. (2014). National Geographic Complete Birds of North America. 2nd edition. National Geographic Society, Washington D.C. Close ). Relatively short but stout bill is yellow, with red gonydeal spot; legs pink, often raspberry pink to rosy; small, pale, beady eyes set centrally but rather high on head; iris yellow, orbital ring pink to purple. Non-breeding adult has dusky-streaked head, neck and breast-sides, while bill is duller yellow and may show a pinkish base and dark subterminal tip (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ). Juvenile variably but rather uniformly velvety greyish-brown on head and body; mantle and scapulars are brown with pale notches. Tertials and wing-coverts show diffuse pale pattern with some barring on the inner greater coverts. Flight-feathers brown, with a contrasting pale window on inner primaries; tail all dark contrasting with paler, spotted uppertail-coverts; bill black, legs pink. First-winter bleached paler, with grey saddle showing some dark streaking; bill begins to show a pinkish base. Second-winter develops a slaty-grey saddle that often contrasts strongly with pale-patterned, whitish wing-coverts. Third-winter resembles adult but retains scattered brown wing-coverts and tail may show broad dark markings (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ).

• Herring x Slaty-backed Gull (hybrid) Larus argentatus x schistisagus
• Glaucous-winged x Slaty-backed Gull (hybrid) Larus glaucescens x schistisagus
• Glaucous x Slaty-backed Gull (hybrid) Larus hyperboreus x schistisagus

NE Siberia from Cape Navarin and Kamchatka S to Vladivostok and Japan (Hokkaido and NE Honshu); also NW Alaska (breeding recorded in Aniktun I) (3 McCaffery, B.J., Harwood, C.M. and Morgart, J.R. (1997). First breeding records of Slaty-backed Gull (Larus schistisagus) for North America. Pacific Seabirds 24(2): 70. Close ). Winters from Bering Sea to Sea of Japan, rarely S to coasts of China and Taiwan (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close , 4 BirdLife International (2013). IUCN Red List for birds. URL: http://www.birdlife.org (download Aug 2013). Close ).

Chiefly frequents inshore coastal waters  but ascends rivers to feed on spawning salmon. Regularly gathers in numbers at fishing ports and at fish-processing factories. Breeds chiefly on coasts; on low sea cliffs, rocky islets, sandy shores or on rocky tops of sea cliffs. Colonies on islands in freshwater lakes in Kamchatka, Russia, are more than 20 km from the sea (5 Zelenskaya, L.A. (2014). Feeding ecology of the Slaty-backed Gull (Larus schistisagus) on Kuril’skoe Lake (southern Kamchatka Peninsula). Biol. Bulletin 41(9): 773–787. Close ).

Many populations non-migratory, dispersing into Bering Sea and Sea of Japan; some migrate S towards coast of China. Winters from Bering Sea to Japan and Taiwan; occurs casually on coasts of China in winter , but vagrant have reached as far south as the Philippines and Indonesia (Lombok) (6 Iqbal, M. and Albayquni, A.A. (2016). First record of a Slaty-backed Gull Larus schistisagus for Indonesia. Marine Orn.. 44(2): 135–136. Close , 7 Nakagun, S., Layusa, C.A.A. and Acebes, J.M.V. (2016). Seabird fauna of the Babuyan Channel and adjacent waters, northern Luzon, Philippines. Marine Ornithology 44(1):43–49. Close ). Non-breeders and wintering birds reach Alaska and occur sparsely but annually on North American Pacific coast S to C California. Vagrants recorded widely in North America, from Yukon, Alberta, S California, Nevada, Colorado, Idaho, Wisconsin, Missouri, Ontario, New York, Texas and Florida (2 Alderfer, J. and Dunn, J.L. eds. (2014). National Geographic Complete Birds of North America. 2nd edition. National Geographic Society, Washington D.C. Close ). There have also been recent records from the W Palearctic, in Latvia, Lithuania, Finland, Belarus, England, Iceland,  Ireland and Poland (8 Millington, R. (2011). The Slaty-backed Gull revisited, in Essex. Birding World. 24(2): 57–60. Close , 9 Anon. (2013). Western Palearctic news Birding World. 25(12): 494–499. Close , 10 Anon. (2012). Western Palearctic news. Birding World. 25(11): 455–460. Close , 11 van den Berg, A.B. (2014). WP reports. Dutch Birding. 36(6): 402–420. Close , 12 Kolbeinsson, Y. (2012). The first Slaty-backed Gull for Iceland. Birding World. 25(5): 211–215. Close ). The spate of N Atlantic and European records has been postulated perhaps to be due not just to increased observer awareness but perhaps also to the recent reduction in Arctic sea ice in summer, that has potentially opened routes linking the Pacific and Atlantic Oceans for longer periods each year (13 Mitchell, D. (2017). Slaty-backed Gull in London and Essex: new to Britain. British Birds. 110(7): 405–413. Close ).

Varied and opportunistic, according to availability. Mainly a wide diversity of fish and invertebrates (e.g. crabs, sea urchins), also carrion , refuse, offal, bird eggs and chicks; occasionally voles and insects. During salmon-spawning , flies upriver to feed on fish and roe (5 Zelenskaya, L.A. (2014). Feeding ecology of the Slaty-backed Gull (Larus schistisagus) on Kuril’skoe Lake (southern Kamchatka Peninsula). Biol. Bulletin 41(9): 773–787. Close ); takes leftovers from bear-kills; eats crowberries (Empetrum nigrum) in late summer; in winter , exploits waste from fisheries and slaughterhouses. Some Hokkaido (Japan) males specialize in predation, piracy and scavenging at seabird colonies, taking adult and young alcids, and chicks of Band-tailed Gulls L. crassirostris , but feed their chicks mostly fish (80%); on Teuri I (N Japan) has a heavy impact on L. crassirostris, especially late in season. Foods utilized vary from colony to colony on Hokkaido, with sardines (Sardinops melanosticta), rock fish (Sebastes spp.), sandeels (Ammodytes spp.) and seabirds in different proportions, depending on year; with crash in sardine stocks, took more birds, sandeels (14 Kazama, K., Sato, M. and Kosugi, K. (2016). Annual variation in breeding numbers of two gull species in response to regional stock size and local availability of Japanese Sand Lance on Rishiri Island, northern Japan. Ornithological Science. 15(1): 85 –94. Close ) and refuse. In Sea of Okhotsk eats mainly adult seabirds , eggs and chicks, taking disproportionate numbers of murrelets (Brachyramphus spp.), Black-legged Kittiwakes (Rissa tridactyla) and Parakeet Auklets (Aethia psittacula). Uses variety of foraging methods, including plunge-diving and surface-plunging.

Resembles L. glaucescens. Long call is slower and deeper than in L. occidentalis (15 Sibley, D.A. (2000). The North American Bird Guide. Pica Press, Robertsbridge, UK. Close ).

Arrives at colonies in Apr in S of breeding range, early Jun in Sea of Okhotsk. Lays from late May in S to early Jun in N. Colonies number dozens to 100s of pairs on low riverine islands, sloping clifftops, and cliff ledges; density often c. 2 nests/m², but more sparse on slopes. Nest of grass, seaweed and feathers, often placed within dense vegetation or among boulders, frequently close to cliff face. Usually three eggs (1–4); incubation 28–30 days, on Kuril Is 31–33 days; chick grey-brown, spotted black above, on breast, and more distinctly on head, with white belly; fed by parents for 40–45 days. Productivity greater among pairs exploiting seabird chicks to feed their young.

Not globally threatened (Least Concern). The global population is not known with any precision but there are 20th century estimates of c. 100,000 pairs. Estimates for Kamchatka population range from 47,000 pairs in more than 200 colonies, to 110,000 pairs. Largest colony (1500 pairs) on Ptichem I, off Karaginskiy I (NE Kamchatka). Hokkaido (Japan) population small, but increasing by perhaps as much as 19% per year in some colonies.