This is an accepted version of this page
| Gull (commonly seagull) Temporal range:Early Oligocene –Present | |
|---|---|
._Saint-Malo%2c_France.jpg) | |
| AdultEuropean herring gull | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Charadriiformes |
| Family: | Laridae |
| Subfamily: | Larinae |
| Genera | |
11,see below | |
Gulls, or colloquiallyseagulls, areseabirds of the subfamilyLarinae. They are most closely related toterns andskimmers, distantly related toauks, and even more distantly related towaders. Until the 21st century, most gulls were placed in the genusLarus, but that arrangement is now consideredpolyphyletic, leading to the resurrection of several genera.[1] An older name for gulls ismews; this still exists in certain regional English dialects and is cognate with GermanMöwe, Danishmåge, Swedishmås, Dutchmeeuw, Norwegianmåke/måse, and Frenchmouette.[2][3][4]
Typically medium to large in size, gulls are usually grey or white, often with black markings on the head or wings. They normally have harsh wailing or squawking calls; stout, longish bills; and webbed feet. Most gulls are ground-nestingpiscivores orcarnivores which take live food or scavenge opportunistically, particularly theLarus species. Live food often includescrustaceans,molluscs, fish and small birds. Gulls have unhinging jaws that provide the flexibility to consume large prey. Gulls are typically coastal or inland species, rarely venturing far out to sea, except for thekittiwakes andSabine's gull.[5] The large species take up to four years to attain full adult plumage, but two years is typical for small gulls.Large white-headed gulls are usually long-lived birds, with a maximum age of 49 years recorded for theEuropean herring gull.[6]
Gulls nest in large, densely packed, noisy colonies. They lay two or three speckled eggs in nests composed of vegetation. The young areprecocial, born with dark mottled down and mobile upon hatching.[7] Gulls are resourceful, inquisitive, and intelligent, the larger species in particular,[8] demonstrating complex methods of communication and a highly developed social structure. For example, many gull colonies displaymobbing behaviour, attacking and harassing predators and other intruders.[9] Certain species, such as the herring gull, have exhibited tool-use behaviour, for example using pieces of bread as bait with which to catchgoldfish.[10] Many species of gulls have learned to coexist successfully with humans and thrive in human habitats.[11] Others rely onkleptoparasitism to get their food. Gulls have been observed preying on live whales, landing on the whale as it surfaces and pecking out pieces of flesh.[12]
Gulls range in size from thelittle gull, at 120 grams (4+1⁄4 ounces) and29 centimetres (11+1⁄2 inches), to thegreat black-backed gull, at 1.75 kg (3 lb 14 oz) and 76 cm (30 in). They are generally uniform in shape, with heavy bodies, long wing, and moderately long necks. The tails of all but three species are rounded; the exceptions beingSabine's gull andswallow-tailed gulls, which have forked tails, andRoss's gull, which has a wedge-shaped tail. Gulls have moderately long legs, especially when compared to the similar terns, with fully webbed feet. The bill is generally heavy and slightly hooked, with the larger species having stouter bills than the smaller species. The bill colour is often yellow with a red spot for the larger white-headed species and red, dark red or black in the smaller species.[13]
Gulls are ageneralist species that can thrive in various environments and survive on a widely varied diet. They are the least specialised of all the seabirds, and their morphology allows for equal adeptness in swimming, flying, and walking. They are more adept walking on land than most other seabirds, and the smaller gulls tend to be more manoeuvrable while walking. The walking gait of gulls includes a slight side to side motion, something that can be exaggerated in breeding displays. In the air, they are able to hover and they are also able to take off quickly with little space.[13]
The general pattern ofplumage in adult gulls is a white body with a darker mantle; the extent to which the mantle is darker varies from pale grey to black. A few species vary in this, theivory gull is entirely white, and some like thelava gull andHeermann's gull have partly or entirely grey bodies. The wingtips of most species are black, which improves their resistance to wear and tear, usually with a diagnostic pattern of white markings. The head of a gull may be covered by a dark hood or be entirely white. The plumage of the head varies by breeding season; in nonbreeding dark-hooded gulls, the hood is lost, sometimes leaving a single spot behind the eye, and in white-headed gulls, nonbreeding heads may have streaking.[13]
Gulls have a worldwidecosmopolitan distribution. They breed on every continent, including the margins ofAntarctica, and are even found in the highArctic. They are less common in thetropics, although a few species do live on tropical islands such as theGalapagos andNew Caledonia. Many species breed in coastal colonies, with a preference for islands; one particular species, thegrey gull, breeds in the interior of dry deserts far from water. Considerable variety exists in theLaridae family, and species may breed and feed in marine, freshwater, or terrestrial habitats.[13]
Most gull species aremigratory, with birds moving to warmer habitats during the winter, but the extent to which they migrate varies by species. Some migrate long distances, notablySabine's gull, which migrates from the Arctic coasts to wintering grounds off the west coasts of South America and southern Africa, andFranklin's gull, which migrates from Canada to winter off the west coast of South America. Other species move much shorter distances and may simply disperse along the coasts near their breeding sites.[13]
A big influence on non-breeding gull distribution is the availability of food patches. Humanfisheries especially have an impact, since they often provide an abundant and predictable food resource.[14] Two species of gulls dependent on human fisheries areAudouin's gull (Ichthyaetus audouinii) andlesser black-backed gulls (Larus fuscus); their breeding distributions (especially the black-backed gull) are heavily impacted by human fishing discards andfishing ports.[14]
Other environmental drivers that structure bird habitat and distribution are human activity and climate impacts. For example, waterbird distribution inMediterraneanwetlands is influenced by changes insalinity, water depth, water body isolation andhydroperiod, all of which have been observed to affect the bird community structure in both a species- andguild-specific way.[15] Gulls in particular have high associations with salinity levels, which were found to be the main environmental predictor for waterbird assemblage.[15]
Charadriiform birds drink salt water, as well as fresh water, as they possessexocrine glands located in supraorbital grooves of the skull by which salt can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance.[16]Gulls are highly adaptable feeders that take a wide range of prey opportunistically. The food taken by gulls includes fish, and marine and freshwaterinvertebrates, both alive and already dead; terrestrialarthropods and invertebrates such as insects and earthworms; rodents, eggs, carrion,offal, reptiles, amphibians, seeds, fruit, human refuse, and even other birds. No gull species is a single-prey specialist, and no gull species forages using only a single method. The type of food depends on circumstances; terrestrial prey, e.g. seeds, fruit and earthworms, is more common during the breeding season, while marine prey is more common in the nonbreeding season when birds spend more time on large bodies of water.[13]
Gulls not only take a wide range of prey, they also display great versatility in how they obtain it; prey can be caught in the air, on water, or on land. A number of hooded species are able tohawk insects on the wing, although the larger species perform this feat more rarely. Gulls on the wing snatch items both off the water and off the ground, and they are able to plunge-dive into water to catch prey. Smaller species are more manoeuvrable and better able to hover-dip fish from the air. Dipping is common when birds are sitting on the water, and gulls may swim in tight circles or foot paddle to bring marine invertebrates up to the surface.
Food is also obtained by searching the ground, often on the shore among sand, mud or rocks. Larger gulls tend to do more feeding in this way. Gulls may also engage in foot paddling in shallow water for invertebrates[17] or on wet grass for earthworms.[18] One method of obtaining prey involves dropping heavy shells of clams and mussels onto hard surfaces.[13] Gulls may fly some distance to find a suitable surface on which to drop shells, and there is evidently a learned component to the task because older birds are more successful than younger birds.[19] While overall feeding success is a function of age, the diversity in both prey and feeding methods is not. The time taken to learn foraging skills may explain the delayed maturation in gulls.[13]
Gulls have only a limited ability to dive below the water surface to feed on deeper prey. To obtain prey from a greater depth, many species of gulls feed in association with other animals, where marine hunters drive prey to the surface when hunting.[13] Examples of such associations include four species of gulls that feed around plumes of mud brought to the surface by feedinggrey whales,[20] and also betweenorcas (the largest dolphin species) andkelp gulls (among other seabirds).[21]
Looking at the effect of humans on gull diet, overfishing of target prey such as sardines have caused a shift in diet and behaviour. Analysis of the yellow-legged gull's (Larus michahellis)pellets off the northwest coast of Spain has revealed a shift from a sardine to crustacean-based diet.[22] This shift was linked to higher fishing efficiency and thus overall fish stock depletion.[22] Lastly, closure of nearby open-air landfills limited food availability for the gulls, further creating a stress on their shift in diet.[22] From 1974 to 1994, yellow-legged gull populations onBerlenga Island, Portugal, increased from 2600 to 44,698 individuals. Analyzing both adult and chick remains, researchers found a mixture of both natural prey and human refuse. The gulls relied substantially on the Henslow's swimming crab (Polybius henslowii). Yet, in times when local prey availability is low, the gulls shift to human-related food. These temporal shifts from marine to terrestrial prey highlight the resilience of adult gulls and their ability to keep chick condition consistent.[23] Human disturbance has also been shown to have an effect on gull breeding, in which hatching failure is directly proportional to the amount of disturbance in a given plot.[24] Certain gull breeds have been known to feast on the eyeballs of baby seals and directly pilfer milk from theelephant seal's teat.[25][26]
Gulls aremonogamous andcolonial breeders that display mate fidelity which normally lasts for the life of the pair. Divorce of mated pairs does occur, but it apparently has a social cost that persists for a number of years after the break-up. Gulls also display high levels ofsite fidelity, returning to the same colony after breeding there once and even usually breeding at the same location within that colony. Gull colonies can vary from just a few pairs to over a hundred thousand pairs, and may be exclusive to that gull species or shared with other seabird species. A few species nest singly, and single pairs ofband-tailed gulls may breed in colonies of other bird species. Within colonies, gull pairs areterritorial, defending an area of varying size around the nesting site from others of their species. This area can be as large as a5-metre radius around the nest in theEuropean herring gull to just a tiny area of cliff ledge in thekittiwakes.[13]
Most gulls breed once a year and have predictable breeding seasons lasting for three to five months. Gulls begin to assemble around the colony for a few weeks prior to occupying it. Existing pairs re-establish theirpair-bonds, and unpaired birds begin courting. Pairs then move back into their territories, and new males establish new territories and attempt to court females. Gulls defend their territories from rivals of both sexes using calls and aerial attacks.[13]
Nest building is an important part of the pair-bonding process. Most gull nests are mats ofherbaceous matter with a central nest cup. Nests are usually built on the ground, but a few species establish their nests on cliffs (the usual preference for kittiwakes), and some choose to nest in trees and high places (e.g.Bonaparte's gulls). Species that nest in marshes need to construct a nesting platform to keep the nest dry, particularly species that nest intidal marshes. Both sexes gather nesting material and build the nest, but the division of labour is not always exactly equal.[13] In coastal towns, many gulls nest on rooftops and can be observed by nearby human residents.
Clutch size is typically three eggs, although some of the smaller gulls only lay two, and the swallow-tailed gull produces a single egg. Birds synchronise their laying within colonies, with a higher level of synchronisation in larger colonies. The eggs of gulls are usually dark tan to brown or dark olive with dark splotches and scrawl markings, and they are well camouflaged. Both sexesincubate the eggs; incubation bouts last between one and four hours during the day, and one parent incubates through the night.[13] Research on various bird species, including gulls, suggests that females form pair bonds with other females to obtainalloparental care for their dependent offspring, a behaviour seen in other animal species, such as elephants, wolves, and thefathead minnow.[27]
Lasting between 22 and 26 days, incubation begins after the first egg is laid but is not continuous until after the second egg is laid, meaning that the first two chicks hatch at about the same time, and the third some time later. Young chicks are brooded by their parents for about one or two weeks, and often at least one parent stays behind to guard the chicks until theyfledge. Although the chicks are fed by both parents, early on in the rearing period the male does most of the feeding and the female most of the brooding and guarding.[13]
Thefamily Laridae was introduced (as Laridia) by the FrenchpolymathConstantine Samuel Rafinesque in 1815.[28][29] Thetaxonomy of gulls is confused by their widespread distribution zones ofhybridisation leading togene flow. Some have traditionally been consideredring species, but research has suggested that this assumption is questionable.[30] Before the 21st century, most gulls were placed in the genusLarus, but this arrangement is now known to bepolyphyletic, leading to the resurrection of the generaIchthyaetus,Chroicocephalus,Leucophaeus,Saundersilarus, andHydrocoloeus.[1] Some English names refer to species complexes within the group:
In common usage, members of various gull species are often referred to as 'sea gulls' or 'seagulls'; however, this is a layperson's term and is not used by most ornithologists and biologists. The name is used informally to refer to a common local species (or all gulls in general) and has no fixed taxonomic meaning.[31] In common usage, gull-like seabirds that are not technically gulls (e.g.albatrosses,fulmars,terns, andskuas) may also be referred to as 'seagulls' by the layperson.
TheAmerican Ornithologists' Union combines theSternidae,Stercorariidae, andRhynchopidae assubfamilies in the family Laridae, but early 21st-century research[32][33][34] shows this to be incorrect.
Amolecular phylogenetic study published in 2022 found the following relationships between the genera, including the most recent generic change: the placement of Saunders's gull in its own genusSaundersilarus.[35]
| Gulls |
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This is a list of the 54 gullspecies, presented intaxonomic sequence.
| Image | Genus | Species |
|---|---|---|
 | LarusLinnaeus, 1758 |
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 | IchthyaetusKaup, 1829 |
|
 | LeucophaeusBruch, 1853 |
|
.jpg) | ChroicocephalusEyton, 1836 |
|
 | SaundersilarusDwight, 1926 |
|
_a_(4834254958).jpg) | HydrocoloeusKaup, 1829 (may includeRhodostethia) |
|
_1_(cropped).jpg) | RhodostethiaMacGillivray, 1842 |
|
.jpg) | RissaStephens, 1826 |
|
_pismo_beach%2c_slo_co%2c_ca_-01_(5156197737).jpg) | PagophilaKaup, 1829 |
|
 | XemaLeach, 1819 |
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 | CreagrusBonaparte, 1854 |
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The Laridae are known from not-yet-publishedfossil evidence since theEarly Oligocene, some 30–33 million years ago. Three gull-like species were described byAlphonse Milne-Edwards from the early Miocene of Saint-Gérand-le-Puy, France. A fossil gull from theMiddle toLate Miocene ofCherry County, Nebraska, US, is placed in the prehistoric genusGaviota;[36] apart from this and the undescribed Early Oligocene fossil, all prehistoric species were tentatively assigned to the modern genusLarus. Among those of them that have been confirmed as gulls, Milne-Edwards'"Larus" elegans and"L." totanoides from the Late Oligocene/Early Miocene of southeastFrance have since been separated inLaricola.[37]
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