Black-headed Gull Chroicocephalus ridibundus Scientific name definitions

37–43 cm; 195–325 g; wingspan 94–110 cm. Two-year gull. The breeding adult has the frontal hood dark chocolate brown to dusky blackish, with blackish border; whiteeye-crescents , mainly behind eye; neck white; underparts white, but in some populations (e.g. in Norway) up to 50% of arriving adults have pink bloom on underparts; back, upperwing-coverts, secondaries and inner primaries grey, secondaries with white tips; outerprimaries white, edged and tipped black; tail white; bill and legs dark red; eye dark brown. Distinguished from slightly larger but very similar Brown-headed Gull (Chroicocephalus brunnicephalus) by largely white leading edge to wing, lacking black wingtip with white subterminal spots. Differs from slightly smaller but almost identical Brown-hooded Gull (Chroicocephalus maculipennis) in having black tips to outermost primaries.Non-breeding adult has whitehead , but retains a dusky spot on ear-coverts and some blackish clouding on nape.

Juvenile has extensive rich buff to darker brown markings on upperparts and upperwing-coverts; black terminal band to tail; bare parts duller. First-winter birds combine an adult-type head and body with juvenile-type wings and tail; the dark-centred tertials are particularly distinctive on settled birds. First-summer birds develop a variable dark hood, duller than in adults, and retain the first-winter plumage, which becomes progressively bleached and worn. Second-winter birds resemble adult-winter but some show complete black webs to the outer 1 or 2 primaries and occasionally dark spots on the primary coverts, alula, tertials and tail (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ).

Some recent authors place this species and other “masked gulls” in genus Chroicocephalus (see Bonaparte's Gull (Chroicocephalus philadelphia)). Sometimes treated as conspecific with Brown-headed Gull, the Pamir population showing characteristics intermediate between the two species. Hybridizes occasionally with Mediterranean Gull (Ichthyaetus melanocephalus) and reportedly with Common Gull (Larus canus) (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ); has hybridized with Slender-billed Gull (Chroicocephalus genei) (2 Fefelov, I.V. (2004). Hybridisation between Slender-billed Gull Larus genei and Black-headed Gull L. ridibundus in Irkutsk, Russia. Forktail 20: 96–97. Close ). NE Siberian population sometimes separated as a geographical race, sibiricus, slightly larger than those in rest of range, but differences minimal. Monotypic.

• Slender-billed x Black-headed Gull (hybrid) Chroicocephalus genei x ridibundus
• Black-headed x Mediterranean Gull (hybrid) Chroicocephalus ridibundus x Ichthyaetus melanocephalus
• Black-headed x Common Gull (hybrid) Chroicocephalus ridibundus x Larus canus
• Black-headed x Ring-billed Gull (hybrid) Chroicocephalus ridibundus x Larus delawarensis

S Greenland and Iceland through most of Europe and C Asia to Kamchatka, extreme SE Russia (Ussuriland) and NE China (Heilongjiang); marginal in E North America (extreme SE Canada and adjacent NE USA). Winters S to W & E Africa, India, and SE Asia.

Temperate zone to edge of boreal forests of Palearctic; mainly at low altitudes, and generally near calm, shallow water of coastal or inland waters, including rivers and their estuaries. Chiefly an inland breeder, with much breeding habitat created by rising water levels, and colonies eventually abandoned when water levels fall and leave dry basin; in many places, however, nests on relatively dry sites, e.g. moors, sand dunes and beaches. Overall, most colonies on freshwater lakes and marshes, but invading certain coastal areas (e.g. coasts of Baltic and North Seas) in huge numbers; in Scandinavia, has recently adapted to colonize salt-marshes, settling ponds, clay pits and coastal dunes and offshore islands. In very wet years may nest in low trees. Often found on sewage farms or near canals.

In winter, tends to occur far more in coastal habitats, but also inland at relatively low elevations. Commonly found in harbours and around sewage outfalls. Seldom far offshore, except on passage. Frequents pastures and farmland, including ricefields, flocks often following the plough. Very large numbers are attracted with other gulls to landfill rubbish dumps: in Iberia this habit has seen a major shift in recent decades towards wintering far inland around major cities instead of on coasts (3 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). Birds that winter inland roost on lakes and reservoirs, often in very large numbers.

Northern populations are migratory, while lower latitude birds tend to be resident or dispersive. Most birds breeding in Switzerland migrate to the W Mediterranean; Scandinavian breeders migrate to Britain and many follow Atlantic coast down to W Africa, but most birds wintering in Britain originate from the Baltic republics. Most of those wintering in Spain originate from France/Belgium, with the remainder largely from northern and eastern Europe: there are recoveries from Spain of birds ringed in almost every European country east to Western Russia, showing that some birds move westwards as well as southwards to winter (3 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). Winters commonly throughout the Mediterranean and Black Sea basins, and in the Caspian Sea.

Abundant in N Africa and the Middle East in winter, chiefly along coasts. Small numbers ascend the River Nile and it is a common visitor to the Red Sea, the Arabian Sea and the Persian Gulf; uncommon along Rift Valley and the E African coast, the winter range having extended to tropical East Africa fairly recently. In West Africa some hundreds at least winter regularly south to Mauritania, Senegal, Ghana and the Cape Verde Islands: there are reports of 3000–4000 in winter from Senegal (4 Isenmann, P., M. Benmergui, P. Browne, A. D. Ba, C. H. Diagana, Y. Diawara, and Z. El Abidine ould Sidaty (2010). Oiseaux de Mauritanie [Birds of Mauritania]. Société d’Études Ornithologiques de France, Paris, France. Close ). Some winter inland in W Africa along the Niger river in Mali and Niger, and in Nigeria and Chad; a few non-breeders oversummer in W Africa (5 Borrow, N., and R. Demey (2001). Birds of Western Africa. Christopher Helm, London, UK. Close ). Vagrants have been recorded widely throughout southern Africa, both inland and on coasts, south to the Cape (6 Sinclair, I., P. Hockey, W. Tarboton, and P. Ryan (2011). Birds of Southern Africa. Fourth edition. Struik Nature, Cape Town, South Africa. Close ).

Asian birds winter S to India, Sri Lanka, Malaysia and Philippines. It is a fairly common migrant and winter visitor to Nepal. Flocks of up to 12,000 occur in Hong Kong in winter, where wintering numbers increased from c. 100 in 1970 to 15,000–20,000 by the mid 1990s (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ). It is abundant throughout Japan from Kyushu northwards in winter, both in coastal waters and inland (7 Shimba, T. (2007). A Photographic Guide to the Birds of Japan and North-East Asia. Christopher Helm, London. Close ). It has become increasingly common in N Borneo in winter, where it is the only gull recorded, especially around Sandokan and Kota Kinabalu (8 Phillipps, Q., and K. Phillipps (2011). Phillipps’ Field Guide to the Birds of Borneo. Sabah, Sarawak, Brunei and Kalimantan. Second edition. John Beaufoy Publishing Ltd, Oxford, UK. Close ). Wintering birds have also become regular in N Wallacea, October–April, particularly in Sulawesi and N Moluccas, and there are records from New Guinea (9 Coates, B. J., and K. D. Bishop (1997). A Guide to the Birds of Wallacea: Sulawesi, The Moluccas and Lesser Sunda Islands, Indonesia. Dove Publications, Alderley, Queensland, Australia. Close , 10 Argeloo, M. (1993). Black-headed Gulls wintering in Sulawesi (and notes on their occurrence elsewhere in the Indo-Australia Region). Kukila. 6(2): 110–114. Close ). Rare vagrants have reached N Australia (11 Palliser, T. and Carter, M. (2013). Rare birds: the 23312 BARC Report. Australian Birdlife. 2(4): 50–53. Close ).

Some Asian birds reach the W Aleutians and Pribilofs outside the breeding season and vagrants have been reported on the N. American Pacific coast from south coastal Alaska south to California. In the East it remains fairly common in Newfoundland, the principal breeding area, in winter, when it also occurs less commonly along the St Lawrence seaway and south along the East coast to New Jersey, with vagrants recorded south to Florida and the Gulf Coast states and throughout the Caribbean and south to Trinidad and Tobago (12 Alderfer, J. and Dunn, J.L. eds. (2014). National Geographic Complete Birds of North America. 2nd edition. National Geographic Society, Washington D.C. Close , 13 Kenefick, M. and Hayes, F.E. (2006). Trans-Atlantic vagrancy of Palearctic birds in Trinidad and Tobago. J. Carib. Orn.. 19(2): 61–72. Close ). There are also records from French Guyana and Colombia (14 Donegan, T., Salaman, P., Caro, D. and McMullan, M. (2010). Revision of the status of bird species occurring in Colombia 2010. Conserv. Colombiana 13: 25–54. Close ). The wintering birds in NE America, several thousand birds, include a proportion from Iceland and Greenland (1 Olsen, K. M., and H. Larsson (2003). Gulls of Europe, Asia and North America. Christopher Helm, London, UK. Close ).

The reported diet is extremely broad and opportunistic but shows a tendency towards a greater reliance on natural foods during the breeding season and on foods of anthropogenic origins in winter (15 Cramp, S., and K. E. L. Simmons, Editors (1983). The Birds of the Western Palearctic. Volume 3. Waders to Gulls. Oxford University Press, Oxford, UK. Close ). The breeding season diet varies according to location but often includes large quantities of aquatic and terrestrial insects as well as earthworms. In Baltic, 93% of stomachs contained insects, 5% molluscs, and 3% each oligochaetes (May only) and fish. Flocks may 'flycatch' flying insects, such as ants or chironomids, when these are abundant (16 Källander, H. (2014). Black-headed Gulls Chroicocephalus ridibundus capturing chironomids in flight: have flight costs been overestimated? Journal of Ornithology. 155(3): 825–827. Close ). Birds nesting at coastal colonies may also rely on marine invertebrates , and to lesser extent on fish. Habitat switching between inshore, intertidal and terrestrial habitats is reported from coastal colonies on the German coast and may be widespread; switching may occur on a daily basis (related to tidal cycle) and over the whole breeding season, the latter switch most probably being the result of lower prey availability in the terrestrial habitats and an increasing quality (in terms of prey abundance and energy intake) of the marine area (17 Schwemmer, P. and Garthe, S. (2008). Regular habitat switch as an important feeding strategy of an opportunistic seabird species at the interface between land and sea. Estuarine Coastal and Shelf Science 77(1): 12–22. Close ).

Feeds by swimming and seizing objects from surface, or dipping head under surface; along coast, by walking on mudflats and probing for shrimps and marine worms; sometimes by foot-stirring and foot-paddling. Also follows fishing boats and ferries that churn up food items, and may feed at night. Plant material is taken opportunistically: it includes fruits and seeds from trees and shrubs in summer in autumn; for example, olives, figs and acorns, and cereal grain from autumn stubble or spring sowings (15 Cramp, S., and K. E. L. Simmons, Editors (1983). The Birds of the Western Palearctic. Volume 3. Waders to Gulls. Oxford University Press, Oxford, UK. Close ). Frequently kleptoparasitic in Europe on Northern Lapwing (Vanellus vanellus) and European Golden-Plover (Pluvialis apricaria) feeding on pastures, where it steals earthworms; also robs Northern Lapwings and other waders on mudflats; kleptoparasitism has been shown to be most effective when practiced by adults, suggesting that it is a skill that is refined over time (18 Barnard, C.J. and Thompson, D.B.A. (1985). Gulls and Plovers. The Ecology and Behaviour of Mixed-species Feeding Groups. Croom Helm, London. Close , 19 Källander, H. (2000). Learning the task: age-related differences in the proficiency of Black-headed Gulls kleptoparasitising Lapwings Abstract HANS Ornis Svecica. 10(1): 7–12. Close ). Occasionally kleptoparasitic on terns and and takes eggs but not chicks of Sandwich Tern (Thalasseus sandvicensis)). In non-breeding season, also relies heavily on various artificial food sources provided by man , especially in W Europe; following fishing boats near harbours, frequenting sewage outfalls, taking scraps in parks and feeding at landfill rubbish dumps. Different individuals have been shown by experiment to develop preferences for either anthropogenic or natural foods in winter, perhaps as a result of early experience (20 Scott, P., Duncan, P. and Green, J. A. (2015). Food preference of the Black-headed Gull Chroicocephalus ridibundus differs along a rural–urban gradient. Bird Study. 62(1): 56–63. Close ).

Notoriously noisy at breeding colonies, producing screaming, downslurred but melodious "krreeaarh" or similar calls, often repeatedly. Feeding flocks often give similar but quieter calls. Also gives a short "kek" or "kekekek" (21 Svensson, L., K. Mullarney, and D. Zetterström (2009). Collins Bird Guide. Second Edition. HarperCollins, London, UK. Close ).

Returns to colonies from late February to late March; lays in late April and May. Most colonies 11–100 pairs, a few exceeding 10,000 pairs; inter-nest distances often average 1 m, and large, bulky nests often touch; solitary nesting generally rare, except in Sweden. Shows strong preference for nesting near vegetation, but some colonies deserted because of vegetation overgrowth; very variable substrate, including sand, vegetation, rocks and marshes. 1–3 eggs (mean 2·6–2·78); incubation 22–26 days; chick warm buff, boldly spotted with irregular black blotches on back and wings and smaller, rounder, sparser black spots on head; mean hatching weight declines from 26 g to 23 g during season; adults and chicks recognize each other by 4th day; fledging by 35 days. Young birds likely to return to breed in natal colony; few breed at 2 years. Recorded longevity of at least 33 years (22 Van Dijk, K., Lutterop, D., Voesten, R. and Majoor, F. (2014). Black-headed Gull of 33 years and re-appeal to stop using aluminium rings to mark gulls Dutch Birding. 36: 249–252. Close ).

Not globally threatened (Least Concern). The global population is estimated at around 4.8–8.9 million individuals. They mainly comprise 3.7–4. million individuals in W Europe together with the W Mediterranean, 770,000–1.8 million birds in E Europe including the Black Sea and E Mediterranean, and 250,000 in W and SW Asia and NE Africa (23 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). Within Europe, national populations approaching or exceeding 100,000 pairs are recently reported from Belarus, the Czech Republic, Finland, Germany, The Netherlands, Poland, Sweden and the United Kingdom, and there may be 200,000–500,000 pairs in Russia.

In the early 1980s the world population was around 2.0 million pairs, following a rapid geographical spread and population increases during 1950–1980, but later increases have been slower and an overall declining trend is now reported, although with clear regional variation Birdlife Datazone . Local factors may be responsible for some observed population changes; for example, at one site in Netherlands, eggs were collected until 1963 in order to protect colonies of Sandwich Terns Thalasseus sandvicensis; when collecting ceased, the population rebounded, increasing from 170 pairs to 6000 pairs in ten years. Similarly, at least formerly, congenital defects attributed in part to chemical pollutants were numerous in Czech and Slovak colonies, affecting 3–5% of eggs, and were particularly common in single-egg clutches.

Westward range expansion across the N Atlantic began early in the 20th century. Iceland and Greenland were colonised in about 1910 and 1969 respectively; the respective populations are recently estimated at 25,000–30,000 pairs and 5–50 pairs respectively (24 BirdLife International (2015). European Red List of Birds. Office for Official Publications of the European Communities, Luxembourg. Close ). In N America records became increasingly frequent from the 1950s onwards and the species first bred in 1977, in E Canada; there are now several small breeding colonies in Canada, west to Quebec but chiefly in Newfoundland, and in New England (12 Alderfer, J. and Dunn, J.L. eds. (2014). National Geographic Complete Birds of North America. 2nd edition. National Geographic Society, Washington D.C. Close ).

Southward range expansion in the W Mediterranean is relatively recent. The first known instance of breeding in the Iberian Peninsula was in 1960 at the Ebro delta; breeding in Spain became increasingly widespread by the late 1970s and there were over 9,000 pairs censused in 2007, at 40 sites, including the Ebro delta which held over 4,000 pairs (25 Molina, B., Editor (2009). Gaviotas reidora, sombría y patiamarilla en España. Población en 2007–2009 y método de censo. SEO/Birdlife Monograph 27. SEO/Birdlife, Madrid, Spain. Close , 3 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). Breeding in Portugal was first reported in 1995 at the Sado estuary but remains minimal (3 de Juana, E., and E. Garcia (2015). The Birds of the Iberian Peninsula. Bloomsbury, London, UK. Close ). The species has been recorded breeding in Morocco since 2002 (26 Radi, M., Qninba, A., Dakki, M. and Thévenot, M. (2004). Nidification de la Mouette rieuse Larus ridibundus et de la Sterne hansel Sterna nilotica sur le lac de barrage d’Al Massira (Maroc central). Alauda. 72(1): 53–58. Close , 27 Rad, M., Aourir, M., Qninba, A., El Mouden, H. and Znari, M. (2017). Premieres donnees sur la reproduction de la Mouette Rieuse Chroicocephalus ridibundus dans le centre-ouest du Maroc. Alauda. 85(2): 131–138. Close ), in Algeria since 2006 (28 Moulay-Meliani, K., Moali, A. and Isenmann, P. (2011). Première nidification de la Mouette rieuse Croicocephalus (Larus) ridibundus en Algérie. Alauda. 79: 79. Close ) and most recently in Tunisia (29 Azafzaf, H., Feltrup-Azafzaf, C., Dlenis, H. and Isenmann, P. (2015). Nouvelles données sur l’avifaune de Tunisie (2005–2014). [New bird records in Tunisia (2005-2014).] Alauda. 83(1): 7–28. Close ).