Black-headed gull

The black-headed gull was formally described in 1766 by the Swedish naturalist Carl Linnaeus in the twelfth edition of his Systema Naturae. He placed it with the other gulls in the genus Larus and coined the binomial name Larus ridibundus. Linnaeus specified the locality as Mari Europaeo or European seas. Genetic studies published early in the 21st century showed that the genus Larus was paraphyletic with respect to other gull genera, and extensive changes to the taxonomy of gulls were made with many species of gull removed from Larus and transferred to other genera. The black-headed gull is now placed with nine other species in the resurrected genus Chroicocephalus that had originally been introduced in 1836 by Thomas Eyton. The genus name Chroicocephalus combines the Ancient Greek χρωικος/khrōikos meaning "coloured" with -κεφαλος /-kephalos meaning "-headed". The specific epithet ridibundus is Latin meaning "laughing". Subspecies Some authorities treat the black-headed gull as a monotypic species with no subspecies, while others treat it as having two subspecies, C. r. ridibundus in the west and centre of the range, and C. r. sibiricus in the far east (eastern Siberia; wintering in Japan and eastern China). The latter is slightly larger and relatively longer-winged. The variation is likely clinal, with intergrades in central Siberia. ==Description==

This gull is long with a wingspan and weighs ; males (186–400 g) average heavier than females (166–350 g), but with considerable overlap. In flight, the white leading edge of the outer wing (the outer primaries) is a good field mark, particularly combined with the dark underside of the inner primaries, which distinguishes it from the white underside of those feathers in its close relative the Bonaparte's gull. The summer adult has a chocolate-brown head (not black, although does look black from a distance), white neck, underparts and tail, pale grey wings and back, black tips to the primary wing feathers, and red bill and legs. The hood is lost in winter, leaving just two dark spots above and behind the eye. Summer plumage occurs from March to July (rarely from late January, and into August), winter plumage from late July until March or April. It breeds in colonies in large reed beds or marshes, or on islands in lakes, nesting on the ground; colonies may range from a few (or even single) pairs up to several thousand pairs, exceptionally over 10,000 pairs. ==Distribution==

Black-headed gulls breed across the Palearctic over much of Europe and northern Asia, from Iceland and Ireland east to Japan and eastern China. They migrate south and west away from regions which freeze hard in winter, reaching northern Africa and southern Asia (with small numbers south to the Equator). Areas within the breeding range with milder winters such as Great Britain receive large influxes of migrants from colder areas like Scandinavia, Poland, the Baltic States, and Russia; the British winter population is around 3 million. Small numbers occur in winter in northeast North America as far south as Virginia, often in flocks of the similar-looking Bonaparte's gull. Vagrancy South of its regular range in eastern North America, it is recorded as a very rare transient south to the Carolina coast, and also in some Caribbean islands and Mexico. and others at Darwin, Northern Territory in 1998, 2005, and 2006. It is also a vagrant south in Africa as far as the Pretoria area in South Africa. ==Disease==

Black-headed gulls were among the birds most heavily hit by the 2023 avian influenza outbreak, with over 4,000 birds killed in Great Britain by early May; similarly high mortality rates were also reported from France, the Netherlands, Italy and Germany. == Behaviour ==

The black-headed gull is a bold and opportunistic feeder. It eats insects, fish, seeds, worms, scraps, and carrion in towns, or invertebrates in ploughed fields with equal facility. Breeding Eggshell removal Eggshell removal is a behaviour seen in birds once the chicks have hatched, observed mostly to reduce risk of predation. The removal is done by both the male and female parents, normally lasts a few seconds and is done three times a year. Earlier hypotheses have attempted to explain the survival value of black-headed gulls removing their eggshells from the nest, including: • The sharp edges of the shells after hatching could harm the chicks The amount and response of begging signals differs throughout the nestling period. Usually, there are 3–5 begging events/hour, each lasting around one minute. High intensity begging behaviour appears at the end of the first week in the nest, but the coordination between multiple chicks emerge during the last week of the nestling period. The more siblings present, the more they coordinate their begging while decreasing the number of begging. Male birds are more likely to be born in the first egg and female birds are more likely to be born in the third. The position of a female black-headed gull in response to the food available when laying the eggs can predict the offspring's characteristics. Conspecific brood parasitism Conspecific brood parasitism is a behaviour that occurs when females lay their eggs in another female's nest, of the same species. It can reduce the cost of incubation and nestling young by passing it on to another bird. Black-headed gulls usually lay three egg clutches, and the first two are normally larger than the third. joint female nesting, and nest takeover. Intra-specific nest parasitism is a disadvantage to the hosts because the female could end up taking care of the parasitic chicks over her own and therefore neglecting them and reducing their fitness. Another disadvantage for the host is that incubating more chicks than their own takes up more energy. Extra-pair paternity The rate of extra-pair paternity (EPP) has a large variation between populations of black-headed gulls. It is primarily a context-dependent strategy, meaning not all black headed gulls experience this behaviour. The differences in the rate of EPP may be determined by multiple different factors: life history traits, ecological factors or different behavioural strategies of males. Central–periphery gradient within colonies Egg-laying can be earlier in Black-headed Gulls nesting in the centre of the colony, with central pairs tending to lay larger eggs, which have a higher hatching success, than pairs nesting at the periphery of the colony. Centrally nesting individuals have also been found to be in better condition and have higher genetic quality. Walking displays Black-headed gulls display both head-bobbing walking (HBW) and non-bobbing walking (NBW). Head-bobbing walking is expressed by a hold phase and a thrust phase. The hold phase in black-headed gulls occurs mainly during the single support phase and is when the bird balances its head to equal the environment. Head-bobbing walking occurs during a seeking type foraging by walking through water and includes benefits such as enhancing motion and pattern detection and gathering depth information from motion parallax during the thrust phase. ==Uses==

The eggs of the black-headed gull were considered a delicacy by some in the UK and eaten hard boiled. ==In popular culture==

The black-headed gull is the official bird of Tokyo, Japan, and the Yurikamome automated guideway transit in Tokyo Bay is named after it. In Richard Adams' 1972 novel Watership Down, a black-headed gull named Kehaar (who claims his name is the onomatopoeia of waves breaking against the shore) plays a major part in the story. Injured by a farm cat and left behind during the seasonal migration, Kehaar finds himself stranded on the Downs and is taken in by a warren of rabbits. He later becomes their friend and ally, and helps to save the rabbits from danger many times; instincts eventually force him to return to his colony, but he promises to visit the rabbits each winter. True to Adams' stated intentions of trying to keep his fictional animals' behaviour close to reality, Kehaar is characterised as intelligent, gregarious, noisy, messy, and impatient, and with a guttural accent. Kehaar appears in all three screen adaptations of the novel; the character was voiced by Zero Mostel in the 1978 film, Rik Mayall in the 1999 TV series, and Peter Capaldi in the 2018 miniseries. ==Gallery==

File:Larus ridibundus MWNH 0380.JPG|Eggs, Collection Museum Wiesbaden, Germany File:Chroicocephalus ridibundus Radès sea.jpg|Chroicocephalus ridibundus, Radès sea, Tunisia File:Black-headed gulls (Chroicocephalus ridibundus) mating.jpg|mating File:Black-headed gulls (Chroicocephalus ridibundus) with chicks.jpg|nesting and with chicks File:Ringing of black-headed gull Chroicocephalus ridibundus nestling.jpg|Ringing a black-headed gull nestling File:Black-headed Gull 2 - St James's Park, London - Nov 2006.jpg|Adult winter plumage in St James's Park, London File:Chroicocephalus ridibundus - closeup of head.jpg|Adult breeding plumage File:Immature black headed gull.jpg|Juvenile plumage File:Black headed gull.jpg|In flight File:Black-headed gull (Chroicocephalus ridibundus) juvenile.jpg|Juvenile at Farmoor Reservoir, Oxfordshire File:Black-headed gull (Chroicocephalus ridibundus) in flight.jpg|At Farmoor Reservoir, Oxfordshire File:Black-headed gull first winter.jpg|First winter plumage, at Blenheim Palace, Oxfordshire File:Black-Headed Gull in flight 140810 1.jpg|In flight near Großenbrode, Schleswig-Holstein; the bird is in a near-vertical position File:Black Headed Gull Navi Mumbai.jpg|From Navi Mumbai, India File:Skrattmås - (Larus ridibundus) - Ystad-2020.jpg|Ringed adult in summer File:Skrattmås (Larus ridibundus) -Ystad-2016.jpg|Juvenile first winter File:Skrattmås (Larus ridibundus) - Ystad-2018.ogg|Black-headed gulls foraging on insects File:Naurulokki 18042024.jpg|Black-headed gull standing on ice in Ämmänväylä, Oulu, Finland File:Black-headed gull.png|A black-headed gull seen from West Sussex, England. File:Mouettes rieuses sur un ponton.jpg|Group of black-headed gulls in winter, France ==References==