Black-tailed Gull Larus crassirostris Scientific name definitions

43–51 cm; 436–640 g; wingspan 126–128 cm. A fairly distinctive gull , medium-sized with a relatively short tail that is black or shows a broad black tail-bar in all plumages. The breeding adult has a white head and underparts, slaty mantle and upperwing, black primaries with only small white tips, white-tipped secondaries and a white tail with a broad, even, black subterminal band ; bill yellow, with red spot at tip and black subterminal ring , the latter with or without a red spot behind on lower mandible; legs yellow. The white head shows dark mottling in winter, particularly as a hindneck bar. The juvenile is dark brown , with pale feather edging above, whitish rump and belly, sooty-brown primaries and a blackish tail; the bill is pinkish with a black tip; white eyelids are conspicuous; legs pinkish. The first-winter develops a uniform dark-brown saddle and is paler-faced. The grey saddle and a grey median covert bar develop by the first-summer, the black tail contrasting with the white rump and uppertail coverts remaining prominent. Third-winter birds resemble adults but show dark markings on the primary coverts and more extensive black in the tail (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ).

SE Russia (Kuril Is, Sakhalin, Moneron I, Popov I, Peter the Great Bay), Japan, Korea and E China (Shandong, Zhejiang (2 Fan Zhongyong, Chen Cangsong, Chen Shuihua, Chan Simba and Lu Yiwei (2011). Breeding seabirds along the Zhejiang coast: diversity, distribution and conservation. Chinese Birds 2(1): 39–45. Close ), Fujian). More widespread in winter, occurring S to N East China Sea.

Coasts , bays and estuaries; breeds on sandy or rocky seashores, sea cliffs, and rocky islets .

Post-breeding dispersal to areas rich in food occur. First-year birds from Peter the Great Bay move to the maritime coast and the Tatar Straits. Birds from NW Honshu fly to the Pacific coast of Honshu , Hokkaido and S Sea of Okhotsk, while those from Yellow Sea spread N and S along its coast. The main wintering areas are in the Sea of Japan and the northern East China Sea, but particularly in the Korea Strait. Smaller numbers winter further south off the Chinese coast, in Taiwan and on the Japanese Pacific coast. The first report from the Philippines was from Cebu in 1991 but more recent records suggest that some may winter regularly in the Babuyan Channel, in the north (3 Redman, N. (1993). Two new species of birds for the Philippines and other notable records. Forktail. 8: 119–123. Close , 4 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 ).

Vagrants reach North America, where first recorded in 1954 (S California); There have been c. 70 records since, mostly in Alaska (April–September), but there are also observations from southern British Columbia south to California (year-round, mostly autumn/winter), with occasional records in the interior (Northwest Territories to the Great Lakes, June–December) and exceptional occurrences on the Atlantic and Gulf coasts (year-round) (5 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ). Vagrants have also reached the Gulf of California, Mexico, Thailand and Australia (6 Garrett, K.I. and Molina, K.C. (1998). First record of the Black-tailed Gull for Mexico. Western Birds. 29: 49–54. Close , 7 Robertson, I.S. (1994). The first sighting of Black-tailed Gull (Larus crassirostris) for Thailand. Natural History Bulletin of the Siam Society. 42: 294. Close , 8 Pizzey, G. and Knight, F. (2007). The Field Guide to the Birds of Australia. 8th edition. HarperCollins, Sidney. Close ).

Diet varies locally and annually. Mainly small fish  , crustaceans, insects and offal; also molluscs and polychaetes. In winter feeds heavily on commercial fish offal. In Hokkaido relied mainly on sardines Sardinops melanosticta but switched to Japanese Sand Lance Ammodytes personatus after the populations of the former crashed in the mid 1980s. The energy-dense Sand Lance remains the most important prey species during the nesting and egg-laying periods in northern Japan, where nesting numbers fluctuate according to the regional Sand Lance stock size (9 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 ). Often follows fishing boats. Steals food from other seabirds, especially auks, gulls and terns (10 Watanuki, Y. (1990). Daily activity pattern of Rhinoceros Auklets and kleptoparasitism by Black-tailed Gulls. Ornis Scandinavica. 21: 28-36. Close ). Visits rubbish dumps. Feeds by surface-seizing, occasionally immersing  ; also plucks prey from surface, and drops hard-shelled items onto hard surfaces to break them open.

A deep mewing "kaoo kaoo", "kau kau" or "yark yark yark". Also a plaintive rasping mewing (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ).

Colonies form mid April, with laying May–June (Siberia). Many colonies hold over 10,000 pairs. Rough nest of dry grass; on sandy or rocky substrate. Clutch 2–3 eggs ; in a Japanese study 60% of females laid 2-egg clutches and the remainder 3 eggs (11 Iseki, K. and Watanuki, Y. (2002). Effects of brood size on chick growth and survival in early and late breeding black-tailed gulls in two years of different environmental conditions. Japanese Journal of Ornithology. 51: 108–115. Close ); incubation 24–25 days, rarely 27 days; chick greyish ochre to reddish ochre, spotted brown-black above and on throat; hatching weight 36–44·5 g; fledging 35–40 days. Predation highest near edge of colony. Fledgling survival 63–70%; main mortality is due to neighbouring adults attacking wandering chicks.

Not globally threatened (Least Concern). The global population is estimated at 1.05 million individuals (12 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ), with sizable concentrations in Peter the Great Bay, Russia, and in Japan, where it is the commonest gull. Colonies suffer some predation, mainly from corvids, and occasionally gulls; at some colonies many chicks may be taken by Slaty-backed Gulls L. schistisagus, particularly late in the season (13 Watanuki, Y. (1982). Size selective hunting by Slaty-backed Gulls Larus schistisagus and influence on fledging success of Black-tailed Gulls L. crassirostris. J. Yamashina Inst. Orn.. 14: 25–34. Close ); feral cats may also take heavy toll. Population control by oiling eggs has been used to reduce numbers on several islands in Matsushima Bay, northeastern Japan, where increased soil nitrogen caused by nesting Black-tailed Gulls has resulted in declines in Japanese Red Pine Pinus densiflora forests (14 Sasaki, C., Mizuta, N., Shimada, T. and Mizota, C. (2011). Hatching control of Black-tailed Gulls for the conservation of Japanese Red Pine Forest in Matsushima Bay, Miyagi Prefecture. Japanese Journal of Ornithology. 60: 73–77. Close ).