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Lesser black-backed gull

The Lesser black-backed gull (Larus fuscus) is a medium to large in the family , distinguished by its slender build, long wings, bright yellow legs, and dark slate-gray mantle in adults, with a reaching up to 1.4 and a body length of approximately 58 cm. Immature birds exhibit brownish that gradually darkens, resembling young herring gulls until the distinctive back color develops. This is primarily Eurasian in , in large colonies on coastal cliffs, islands, and increasingly urban rooftops from and to , while small populations have established in and the since 2016; it winters across a broad range including the Atlantic coasts of , , and , where it is a regular but non- visitor to areas like the mid-Atlantic states and . It favors diverse habitats such as shorelines, estuaries, lakes, rivers, landfills, and agricultural fields, often associating with human activity for foraging. Omnivorous and opportunistic, the lesser black-backed gull feeds on , , , carrion, eggs, small mammals, berries, and human refuse, employing techniques like surface-plunging dives, dropping to crack them open, or scavenging behind trawlers. It is generally monogamous and territorial, nesting in dense colonies where pairs build nests of vegetation and debris, laying 1–4 eggs that are incubated for about 28 days; both parents share chick-rearing duties, which last around 35–40 days until fledging. Vocalizations include a variety of calls such as long calls during territory defense and "choking" displays in . The global population exceeds 1 million individuals and is considered of least concern by the IUCN, though regional declines have occurred in parts of the due to historical use and predation, while numbers remain stable or increasing elsewhere in . Notable behaviors include forming "loafing clubs" near colonies for resting and , occasional hybridization with herring gulls, and where it steals food from other s. records show individuals surviving up to 34 years.

Taxonomy

Classification

The lesser black-backed gull (Larus fuscus) was first formally described by the Swedish naturalist in the 10th edition of his in 1758, where it was named based on specimens from , with the type locality later restricted to . The species is placed in the genus within the family Laridae, which encompasses gulls, terns, and skimmers. It is closely related to other large white-headed gulls, particularly the herring gull (Larus argentatus) and the (Larus michahellis), forming part of a characterized by overlapping morphologies and hybridization potential. The specific epithet "fuscus" derives from the Latin word for "dark" or "dusky," referring to the distinctive dark gray to blackish mantle and upperwing coloration of the adult bird. Historically, the taxonomy of the lesser black-backed gull has been subject to debate, particularly regarding the status of certain eastern forms. For instance, Heuglin's gull (Larus heuglini), originally described as a distinct species in 1844, was long recognized separately due to its paler plumage and broader distribution across Siberia and Central Asia; however, molecular and morphological analyses have since reclassified it as a subspecies (L. f. heuglini) within L. fuscus. This reassessment reflects broader challenges in delimiting species boundaries in the Larus complex, where gene flow and clinal variation complicate traditional classifications. Phylogenetic studies based on mitochondrial DNA sequences indicate that the lesser black-backed gull diverged from closely related Larus species, such as the herring gull, during the early Pleistocene, approximately 1–2 million years ago, likely driven by glacial cycles and geographic isolation in the Holarctic region. This radiation within the large white-headed gull clade highlights a pattern of recent evolutionary diversification, with ongoing introgression further blurring phylogenetic lines among taxa.

Subspecies

The lesser black-backed gull (Larus fuscus) is classified into five , characterized by clinal variation in , particularly mantle coloration ranging from pale slate-gray to blackish, along with differences in and leg hue, increasing from west to east across their Palearctic range. These subspecies are supported by genetic evidence, including analyses revealing population structure and divergence that validate their taxonomic distinctions, particularly among the western forms. L. f. graellsii, the nominate western subspecies, features the palest slate-gray and bright yellow legs, with a relatively smaller size compared to eastern forms. It breeds primarily in , the , the , and extends to northwestern and , wintering along the coasts of southwestern to , with occasional vagrants reaching the . L. f. intermedius exhibits an intermediate dark gray mantle and yellow legs, serving as a transitional form between the paler graellsii and darker fuscus. This subspecies breeds in , from the and through , southern , and southwestern to northeastern , with wintering grounds in and . L. f. fuscus, the darkest-mantled subspecies with a blackish back and typically yellow (occasionally pinkish) legs, is confined to breeding in the , northern , and the area of . It migrates southward to winter in , including and . L. f. heuglini, formerly recognized as a distinct species (Heuglin's gull), is larger-bodied with a slate-gray similar to graellsii but with longer wings and pinkish-yellow legs. It breeds in northern from the eastward to the and migrates to winter along Pacific and coasts, from the through , , eastern China, and , with rare occurrences in . L. f. barabensis, the easternmost and paler steppe form with a light gray mantle and variable leg color, breeds in central Asian steppes from northeastern to northeastern . Its non-breeding range centers on southwestern .

Description

Physical characteristics

The lesser black-backed gull (Larus fuscus) is a medium to large gull with a body length of 52–64 cm, a wingspan of 135–150 cm, and a weight ranging from 545–1,000 g. It exhibits a slender build relative to other large gulls, characterized by long, pointed wings that project noticeably beyond the tail when perched or in flight, relatively short legs, and a robust featuring a distinct gonys . In adults, the bill is bright yellow with a prominent red spot at the gonys, the eye-ring is red, and the legs are yellow. The shows sexual size dimorphism, with males approximately 10–20% larger than females overall and no major differences in between the sexes. Compared to similar , it is smaller and slimmer than the (Larus marinus) while having a darker slate-gray back than the herring gull (Larus argentatus).

Plumage variations

The lesser black-backed gull exhibits distinct variations across its four-year maturation cycle, with seasonal changes primarily affecting the head and in adults. In , adults display a slate-gray and upperwing coverts, pure white head and underparts, black primary wingtips marked by white subterminal spots (mirrors) on the tenth and sometimes ninth primaries, a yellow with an orange-red gonydeal spot, and bright yellow legs. During the non-breeding winter phase, the head and neck develop fine brown streaking, while the 's red spot becomes less vivid, though the overall body coloration remains similar. Juveniles emerge with a scaly brown back formed by dark-centered feathers with pale fringes, mottled gray-brown underparts, pale-edged greater coverts creating a wing pattern, dark chocolate-brown primaries and secondaries, and a broad blackish tail band. In first-winter , following a partial pre-basic molt, the scaling persists but fades, with the blackish and legs flesh-colored. By second-winter, after the first complete pre-basic molt, the mantle shows mottled slate-gray feathers with brownish margins, the wings retain dark remiges without white markings, the head is whitish with brown streaks, and the tail band narrows but remains dark. Third-winter birds approach adult appearance post-molt, featuring a mostly solid slate-gray mantle with some brown-fringed coverts, blackish wingtips lacking full mirrors, a largely with a dark subterminal band, and straw- legs, while the tail is nearly white. Full adult plumage is attained in the fourth after the third pre-basic molt, with subsequent annual cycles involving a complete pre-basic molt () replacing body and , and a partial pre-alternate molt (December–April) refreshing head and body feathers for . differences among primarily involve mantle shade: the nominate L. f. fuscus has the darkest, near-blackish upperparts ( Gray Scale 13–15), while L. f. graellsii is paler slate-gray (9–11), and L. f. intermedius intermediate (11–13).

Distribution and habitat

Breeding distribution

The lesser black-backed gull (Larus fuscus) primarily breeds along the Atlantic and coasts of , ranging from and the eastward to in the east, encompassing , the , and parts of northern , , , and the . This reflects a preference for temperate to coastal environments, with the bulk of the population concentrated in . Subspecies exhibit subtle range variations; for instance, the nominate L. f. fuscus is restricted to , the , and Baltic coasts of , and . Breeding habitats favor coastal features such as cliffs, rocky islands, saltmarshes, and dunes, where colonies form on level ground with short, dense vegetation for and accessibility. Inland sites, including freshwater lakes and urban rooftops in , support expanding populations, particularly in urbanized areas like the and . Nesting is colonial, with densities varying from low (around 7 pairs per ) in sparse sites to high (up to 192 pairs per ) in optimal coastal colonies, allowing for communal against predators. The European breeding population comprised an estimated 394,000–460,000 pairs as of 2015, accounting for nearly the entire global total, with the supporting about 110,000 pairs as of 2000–2002—roughly 25% of the European figure at that time and concentrated in fewer than ten major sites. Recent monitoring indicates declines at some UK colonies, including up to 25% at natural sites between 2021 and 2023 due to highly pathogenic (HPAI). Small-scale expansion has occurred into , with breeding colonies established in since the 1990s, though numbers remain limited. Breeding occurs predominantly in lowlands near , extending occasionally to elevations around 500 m in inland or upland coastal margins.

Non-breeding distribution and migration

The lesser black-backed gull exhibits varied migratory behaviors depending on subspecies. Northern populations, such as the nominate Larus fuscus fuscus breeding in Scandinavia and the Baltic region, are long-distance migrants that primarily winter in eastern and central Africa, with some individuals reaching the eastern Mediterranean, Middle East, or northwest Africa along coastal routes. In contrast, southern subspecies like L. f. graellsii, which breed in Britain, Iceland, and western Europe, are partially migratory; many remain resident or dispersive within the British Isles and western Europe year-round, while others move southward to subtropical West Africa. Wintering grounds span from the and coastal southward to tropical , where birds exploit marine and coastal resources. In recent decades, the species has shown a marked increase in , particularly along the Atlantic coast from to , with smaller numbers reaching the and Gulf Coast; these non-breeding visitors, observed annually in thousands, are predominantly of the graellsii from Icelandic and Greenlandic breeding origins. Migration typically involves post-breeding dispersal beginning in late July to August, with adults departing breeding colonies earlier than juveniles, followed by southward movements along the Atlantic flyway that peak from September to November; northward return migration occurs from March to May, timed with the thawing of northern breeding grounds. Birds often follow coastal corridors or associate with fishing vessels to minimize energy expenditure during transit. Vagrancy records highlight the species' exploratory tendencies, with rare occurrences along the Pacific coast of North America, such as in California, where sightings remain sporadic despite gradual increases. In Asia, vagrants are uncommon outside the western breeding range, typically limited to coastal areas. Recent genetic and population analyses trace many North American vagrants to rapidly expanding Greenlandic populations, with earlier influxes linked to Icelandic sources, underscoring how population growth drives transatlantic dispersal. During the non-breeding season, lesser black-backed gulls favor coastal estuaries, harbors, beaches, and open ocean, but also adapt to inland sites including rivers, lakes, marshes, fields, and urban landfills, where they scavenge diverse food sources. This flexibility supports their presence in human-modified environments across winter ranges.

Reproduction

Breeding biology

The lesser black-backed gull typically breeds from to July in northern parts of its range, such as the and , with arrival on breeding grounds occurring from late to early May and egg-laying concentrated between and ; in southern regions like the Mediterranean, breeding commences earlier, often by late . Pairs are generally and exhibit strong fidelity, often maintaining bonds across multiple breeding seasons, though serial monogamy can occur if previous attempts fail. First breeding usually happens at 4–5 years of age, with some individuals delaying until 7 years. Courtship involves a combination of aerial and ground displays to establish and reinforce pair bonds. Aerial rituals include sky-pointing, where the flies upward with wings raised and head tilted skyward, often accompanied by long calls—a series of high-pitched, drawn-out notes delivered with the outstretched. Ground behaviors feature head-tossing, in which the bird rapidly flicks its head back while calling, as well as mutual of head and feathers and food solicitation by the through upward movements, prompting the to regurgitate food. These displays, along with postures (head lowered with ), help synchronize the pair and advertise territory. Breeding occurs in large colonies ranging from hundreds to thousands of pairs, often on coastal islands, cliffs, or inland rooftops, where aggressive territory defense is prominent. Both sexes vigorously protect a small area around the nest site using long calls, alarm chuckles, and physical attacks like pecking or wing-slapping against intruders. Clutch size is typically 3 eggs (range 1–4), laid at intervals of 1–2 days, with both parents sharing duties for 24–27 days until hatching. Chicks are semi-precocial, downy, with eyes open and capable of limited mobility, but remain brooded and dependent, fledging after 35–40 days.

Nesting and parental care

The lesser black-backed gull typically constructs its nest as a shallow scrape on the ground, often on vegetated coastal islands, isolated beaches, cliff edges, or urban rooftops, with nests spaced variably in colonies—ranging from about 2.6 m nearest neighbor distance in dense sites to 10-50 m in looser arrangements. Both sexes participate in building the mound-like structure, lining a central cup with grasses, , , lichens, feathers, and other debris for and . Nests with substantial surrounding (>300° coverage) enhance success by reducing predation exposure. The female lays a of 1-4 s, most commonly 3, at intervals of 1–2 days, with each measuring approximately 67 x 47 mm and featuring an olive-buff to brown or blue-green ground color blotched with dark brown spots. Both parents incubate the s for 24-27 days, with the female handling most of the early duties. Upon hatching, the semi-precocial emerge gray-brown, with and capable of limited within hours, though they remain brooded by the for the first few days to regulate . success averages around 76-94% in three-egg clutches, influenced by egg size (larger eggs hatch better), laying date (mid-season optimal), and nest concealment, with about 1.9 eggs hatching per pair on average. Parental care is biparental throughout the chick-rearing period, with both adults regurgitating partially digested food—often , , or terrestrial items like —to provision the young near the nest site. Adults aggressively defend the brood against predators such as foxes, , and conspecific through alarm calls, upright postures, and physical attacks involving pecks and wing strikes, with males often leading territorial displays. Chicks become independent at 6-7 weeks, fledging after 35–40 days but continuing to receive supplemental feeding from parents for several additional weeks while learning skills; overall success yields 0.5-1.6 fledglings per pair, varying with predation, weather, and food availability.

Ecology and behavior

Feeding habits

The lesser black-backed gull (Larus fuscus) exhibits an omnivorous that varies significantly by region and , incorporating , terrestrial, and sources. In coastal and northern populations, prey dominates, with such as gadoids (e.g., saithe), , and sandeels comprising up to 74-81% of diets by aggregate percent by prey mass and frequency of occurrence in pellets. Crustaceans, mollusks (e.g., zebra mussels), and marine worms also feature prominently, while terrestrial components include , earthworms, and small vertebrates like or . In contrast, inland populations rely heavily on terrestrial and human-derived foods, with refuse in 61% of regurgitated boluses (e.g., , , plastics), beetles in 84% of pellets, and moles in 36% of pellets, and no food remains found in samples (only 0.3% of trips to the sea). Carrion, eggs, and nestlings of other supplement the diet opportunistically across habitats. Dietary composition shifts seasonally to meet nutritional demands. During the breeding season, adults and parents prioritize high-protein marine fish to provision chicks, enhancing growth and reproductive success through nutrient-rich items like and gadoids. In winter and non-breeding periods, reliance increases on scraps and refuse from landfills or fisheries, reflecting opportunistic in altered environments. provides an additional strategy, with lesser black-backed gulls stealing prey from other seabirds to supplement their intake without direct capture efforts. Like other scavenging , it has strong gastric acidity ( typically 1-2), enabling safe consumption of carrion and potentially contaminated refuse by neutralizing pathogens. Their slender, hooked bill facilitates surface-pecking for and probing soft substrates for or crustaceans, while maintaining on mixed diets without reduced digestive performance. Adults require substantial energy, consuming food equivalent to 900-1400 kJ daily in captivity (primarily from , with 75% ), while juveniles receive prioritized high-protein feeds like to support rapid development. Stable isotope analyses (δ¹³C and δ¹⁵N) confirm regional diet variability, with coastal birds showing signatures (enriched δ¹³C) and urban or inland individuals exhibiting depleted values indicative of higher and terrestrial input, such as refuse in landfills. This flexibility underscores the species' adaptability but highlights dependency on human-altered food webs in populated areas.

Social and migratory behavior

The lesser black-backed gull exhibits highly gregarious outside the breeding season, forming large flocks numbering in the thousands at communal roosts and feeding sites, where individuals engage in resting, , and social interactions. These flocks often include mixed-species assemblages with other and waterbirds, facilitating collective opportunities. Within feeding groups, dominance hierarchies emerge based on age and size, with adults typically asserting priority access to food resources through aggressive displays such as pecking and chasing, while juveniles and smaller individuals are frequently displaced by larger conspecifics or sympatric species like the herring gull. Foraging techniques among lesser black-backed gulls are diverse and opportunistic, including surface-dipping for , plunge-diving from heights of up to several meters to capture , and scavenging at human waste sites such as landfills and discards. , or food , is a notable strategy, with individuals attempting to steal prey from other seabirds; success rates in such interactions average around 26-37% depending on the context and victim , though this behavior constitutes a minor but regular component of their foraging repertoire in some populations. These techniques are often performed in loose flocks, enhancing efficiency through information sharing about food patches. Vocalizations play a key role in social communication, with over 10 distinct call types documented, including —a series of descending, higher-pitched notes used to advertise territory and pair bonds—and the mew call, a shorter, alarm-like signaling threats or intruders. Other calls, such as the kyow and displays, facilitate greetings and warnings during group interactions. These vocal signals are particularly prominent in colonies, where they help maintain spacing and coordinate defenses against predators. During migration, lesser black-backed gulls undertake diurnal flights in loose, flexible flocks, often utilizing and breezes to cover distances efficiently, with daily distances averaging around 175 km on travel days and overall speeds up to 50 km/h depending on wind conditions. Navigation relies on a combination of visual cues, including coastal landmarks for route-following and celestial orientation via stars during nocturnal segments, enabling precise orientation over long distances from breeding grounds in to wintering areas in the Mediterranean and . Social interactions extend to interspecific relations, where lesser black-backed gulls aggressively defend colony territories against intruders through dives, calls, and physical confrontations, occasionally preying on eggs or nestlings of smaller seabirds. Rare hybridization occurs with the herring gull in overlap zones, producing intermediates with mixed and leg coloration, though such events are infrequent and do not significantly impact .

Conservation

Population status

The lesser black-backed gull (Larus fuscus) has a global population estimated at 940,000–2,070,000 individuals (as of 2015), with the vast majority breeding in . The species is classified as Least Concern on the , based on a 2018 assessment that remains current as of 2025, reflecting an overall stable to increasing trend despite regional variations. Population monitoring is primarily conducted by organizations such as and , which provide key estimates and trend assessments. In , the breeding population is estimated at 394,000–460,000 pairs (as of 2015), representing approximately 788,000–920,000 mature individuals and comprising the core of the global total. The breeding population in the was estimated at 110,000 pairs during 1998–2002, with and together accounting for roughly 40% of the population; however, numbers have since declined by approximately 25% based on the Seabirds Count (2015–2021), but it is Amber-listed due to moderate declines observed in national surveys. For instance, numbers have decreased by more than 22% over the past two decades, with a 48% drop in between the Seabird 2000 census (1998–2002) and the Seabirds Count 2015–2021 survey. Regarding subspecies, the nominate L. f. fuscus (northern European form) has experienced declines linked to environmental contaminants but shows stability or recovery in specific areas, such as the Swedish islands of Stora Karlso and Lilla Karlso, where populations rebounded from lows based on censuses. The western L. f. graellsii, predominant in and (hosting ~87% of its global breeding population), has seen historical increases but recent contractions in line with broader regional trends. Surveys in the indicated partial recoveries post- declines for fuscus in parts of , contributing to the ' overall .

Threats and management

The lesser black-backed gull has faced historical threats from human persecution, including egg collecting and shooting, particularly in the UK where such activities contributed to population declines until the mid-20th century. In the 19th century, widespread persecution across Europe led to significant reductions, but populations rebounded following legal protections that curtailed these practices. Current threats include habitat loss from coastal development and urbanization, which reduces suitable nesting sites and forces shifts to urban areas. Pollution, particularly heavy metals and organochlorines like DDE and PCBs, accumulates in eggs and affects northern subspecies, contributing to reproductive issues and local declines. Climate change exacerbates these pressures by altering fish stocks, a key food source, and increasing storm frequency that disrupts breeding colonies. Predation has intensified in urban and coastal colonies due to expanding red fox populations, leading to higher nest losses and colony abandonment in areas like northern England and Wales. Additionally, collisions with wind turbines pose risks during migration and foraging, especially for offshore populations in the North Sea. In recent years, the 2021–2022 outbreak of highly pathogenic avian influenza (HPAI H5N1) has led to substantial mortality, contributing to further population declines, including a 25% overall reduction in the UK and up to 58% in Scotland as of 2023. Management efforts focus on legal protections and targeted interventions to mitigate threats. The species is safeguarded under the EU Birds Directive (Annex II) and the African-Eurasian Migratory Waterbird Agreement, which promote across its range. In the UK, programs are implemented at airports to reduce bird strike hazards, with licenses allowing controlled removal of pairs. Habitat restoration initiatives, such as island management in , involve vegetation control and predator exclusion to enhance nesting success amid declining populations. These measures have supported overall population stability, classified as Least Concern globally. Research gaps persist, particularly regarding the long-term impacts of ingestion, which accumulate through scavenging and may impair and , though studies on related highlight potential sublethal effects. Ongoing investigations from 2021 to 2025 explore vagrancy patterns and their role in , using data to predict source populations and inform connectivity models. A notable success story is the rebound in , where pairs increased from 1,250 in 1974 to over 40,000 by 2004, attributed to reduced persecution and improved habitat conditions.

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