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Gull (commonly seagull)
Temporal range:Early Oligocene–Present
AdultVega gull
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Charadriiformes
Suborder: Lari
Family: Laridae
Genera

11, see text

Juvenile ofArmenian gullin flight, flying overLake Sevan

Gulls,or colloquiallyseagulls,areseabirdsof the familyLaridaein the suborderLari.They are most closely related to theternsandskimmersand distantly related toauks,and even more distantly 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,which is cognate with GermanMöwe,Danishmåge,Swedishmås,Dutchmeeuw,Norwegianmåke/måse,and Frenchmouette,and can still be found in certain regional dialects.[2][3][4]

Gulls are typically medium to large in size, usually grey or white, often with black markings on the head or wings. They typically have harsh wailing or squawking calls; stout, longish bills; and webbed feet. Most gulls are ground-nestingcarnivoreswhich take live food or scavenge opportunistically, particularly theLarusspecies. Live food often includes crustaceans, mollusks, fish and small birds. Gulls have unhinging jaws which allow them to consume large prey. Gulls are typically coastal or inland species, rarely venturing far out to sea, except for thekittiwakes.[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 gullsare typically long-lived birds, with a maximum age of 49 years recorded for theherring 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 displaymobbingbehavior, attacking and harassing predators and other intruders.[9]Certain species have exhibited tool-use behavior, such as the herring gull, using pieces of bread as bait with which to catchgoldfish,for example.[10]Many species of gulls have learned to coexist successfully with humans and have thrived in human habitats.[11]Others rely onkleptoparasitismto get their food. Gulls have been observed preying on live whales, landing on the whale as it surfaces to peck out pieces of flesh.[12]

Description and morphology

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ThePacific gullis a large white-headed gull with a particularly heavy bill.

Gulls range in size from thelittle gull,at120 grams (4+1⁄4ounces) and29 centimetres (11+1⁄2inches), 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 gullandswallow-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]

The gulls are generalist feeders. Indeed, 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 ofplumagein 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 gullis entirely white, and some like thelava gullandHeermann's gullhave 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]

Distribution and habitat

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See also:List of Charadriiformes by population
Swallow-tailed gullsare endemic to the Galapagos Islands.

The gulls have a worldwidecosmopolitan distribution.They breed on every continent, including the margins ofAntarctica,and are found in the high Arctic as well. They are less common on tropical islands, although a few species do live on islands such as theGalapagosandNew Caledonia.Many species breed in coastal colonies, with a preference for islands, and one species, thegrey gull,breeds in the interior of dry deserts far from water. Considerable variety exists in the 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, likeFranklin's gull,which migrates from Canada to wintering grounds in the south of South America. Other species move much shorter distances and may simply disperse along the coasts near their breeding sites.[13]

Gulls in the coat of arms ofHaugesund.

A big influence on non-breeding gull distribution are food patches. Human fisheries especially have an impact since they often provide an abundant and predictable food resource.[14]Looking at two species of gulls dependent on human fisheries, Audouin (Ichthyaetus audouinii) and black-backed gulls (Larus fuscus),their breeding distributions (especially the black-backed gull) was heavily impacted by human fishing discards and fishing ports.[14]

Looking further at environmental drivers that structure bird habitat and distribution are human and climate impacts. Looking at waterbird distribution in wetlands, changes in salinity, water depth, water body isolation and hydroperiod altered bird community structure in both a species and guild specific way.[15]Gulls in particular had high associations with salinity levels, being the main environmental predictor for waterbird assemblage.[15]

Behaviour

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Diet and feeding

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Charadriiform birdsdrink salt water, as well as fresh water, as they possessexocrine glandslocated 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 opportunistically take a wide range of prey. The food taken by gulls includes fish and marine and freshwater invertebrates, both alive and already dead; terrestrialarthropodsand 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, and terrestrial prey such as seeds, fruit, and earthworms are 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]

Hartlaub's gullfoot paddling, Cape Town

In addition to taking a wide range of prey, gulls display great versatility in how they obtain prey. Prey can be obtained in the air, on water, or on land. In the air, a number of hooded species are able tohawkinsects on the wing; larger species perform this feat more rarely. Gulls on the wing also snatch items both off water and off the ground, and over water they also plunge-dive to catch prey. Again, smaller species are more manoeuvrable and better able to hover-dip fish from the air. Dipping is also 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. In shallow water gulls may also engage in foot paddling.[17]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 apparently a learned component to the task exists, as older birds are more successful than younger ones.[18]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 to feed on deeper prey. To obtain prey from deeper down, 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 feeding around plumes of mud brought to the surface by feedinggrey whales,[19]and also betweenorcas(largest dolphin species) andkelp gulls(and other seabirds).[20]

Looking at the effect of humans on gull diet, overfishing of target prey such as sardines have caused a shift in diet and behavior. Analysis of yellow-legged gull's (Larus michahellis)pelletsoff the northwest coast of Spain revealed a shift from a sardine to crustacean-based diet.[21]This shift was linked to higher fishing efficiency and thus overall fish stock depletion.[21]Lastly, closure of nearby open-air landfills limited food availability for the gulls, furthering creating a stress on their shift in diet.[21]Between the years of 1974–1994, yellow-legged gull populations in Berlenga 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 a marine to terrestrial prey highlight the resilience adult gulls have and their ability to keep chick condition consistent.[22]Human disturbance has also shown to have an effect on gull breeding, in which hatching failure is directly proportional to the amount of disturbance in a given plot.[23]Certain gull breeds have been known to feast on the eyeballs of baby seals, and directly pilfer milk from theelephant seal's teat.[24][25]

Breeding

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Black-legged kittiwakesnest colonially, but have tiny, closely packed territories.
The nest of agreat black-backed gull,with three typical eggs
Two ring-billed gull chicks sitting amongst rocks

Gulls aremonogamousandcolonialbreeders that display mate fidelity that usually 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 in the same location within that colony. 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 gullsmay breed in colonies of other birds. 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 a 5-m radius around the nest in theherring gullto 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 the colony. Existing pairs re-establish their pair-bonds, and unpaired birds begin courting. Birds 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 through calls and aerial attacks.[13]

Nest building is also part of the pair-bonding. Gull nests are usually mats of herbaceous matter with a central nest cup. Nests are usually built on the ground, but a few species build nests on cliffs, including the kittiwakes, which almost always nest in such habitats, and in some cases in trees, and high places likeBonaparte's gulls.Species that nest in marshes must construct a nesting platform to keep the nest dry, particularly in species that nest in tidal 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 sizeis typically three eggs, although it is two in some of the smaller species and only one egg for the swallow-tailed gull. Within colonies, birds synchronise their laying, with synchronisation being higher in larger colonies, although after a certain point, this levels off. The eggs of gulls are usually dark tan to brown or dark olive with dark splotches and scrawl markings, and are well camouflaged. Both sexes incubate the eggs, with incubation bouts lasting between one and four hours during the day and one parent incubating through the night.[13]Research on various bird species including the gull suggests that females form pair bonds with other females to obtainalloparental carefor their dependent offspring, a behavior seen in other animal species, like the elephants, wolves, and thefathead minnow.[26]

Incubation lasts between 22 and 26 days, and begins after laying the first egg, although it is discontinuous until the second egg is laid. This means the first two chicks are born close together, and the third chick some time later. Young chicks are brooded by their parents for about one or two weeks, and often at least one parent remains with them, until theyfledge,to guard them. Both parents feed the chicks, although early on in the rearing period, the male does most of the feeding and the female most of the brooding and guarding.[13]

Black-tailed gulls following a ferry inMatsushima,Japan

Taxonomy

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The family Laridae was introduced (as Laridia) by the FrenchpolymathConstantine Samuel Rafinesquein 1815.[27][28]Thetaxonomyof gulls is confused by their widespread distribution zones ofhybridizationleading togeneflow.Some have traditionally been consideredring species,but recent[when?]evidence suggests that this assumption is questionable.[29]Until recently, 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, "seagull" is a layperson's term that is not used by most ornithologists and biologists. This name is used informally to refer to a common local species or all gulls in general, and has no fixed taxonomic meaning.[30]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.

Western gullat Point Lobos State Natural Reserve, California, US

TheAmerican Ornithologists' Unioncombines theSternidae,Stercorariidae,andRhynchopidaeassubfamiliesin the family Laridae, but recent[when?]research[31][32][33]indicates this is incorrect.

Amolecular phylogeneticstudy published in 2022 found the following relationships between the genera. Some authorities place the Saunders's gull in its own genusSaundersilarus.[34]

Gulls

Creagrus– swallow-tailed gull

Hydrocoloeus– little gull

Rhodostethia– Ross's gull

Rissa– kittiwakes (2 species)

Xema– Sabine's gull

Pagophila– ivory gull

Chroicocephalus saundersi– Saunders's gull

Chroicocephalus– (10 species)

Leucophaeus– (5 species)

Ichthyaetus– (6 species)

Larus– (24 species)

List of species

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This is a list of the 54 gullspecies,presented intaxonomic sequence.

Image Genus Species
LarusLinnaeus, 1758
IchthyaetusKaup, 1829
LeucophaeusBruch, 1853
ChroicocephalusEyton, 1836
HydrocoloeusKaup, 1829(may includeRhodostethia)
RhodostethiaMacGillivray, 1842
RissaStephens, 1826
PagophilaKaup, 1829
XemaLeach, 1819
CreagrusBonaparte, 1854

Evolutionary history

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The Laridae are known from not-yet-publishedfossilevidence since theEarly Oligocene,some 30–33 million years ago. Three gull-like species were described byAlphonse Milne-Edwardsfrom the early Miocene of Saint-Gérand-le-Puy, France. A fossil gull from theMiddletoLate MioceneofCherry County, Nebraska,US, is placed in the prehistoric genusGaviota;[35]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" elegansand"L." totanoidesfrom the Late Oligocene/Early Mioceneof southeastFrancehave since been separated inLaricola.[36]

References

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Further reading

[edit]
[edit]
Look upgullin Wiktionary, the free dictionary.
Wikimedia Commons has media related toLaridae.
Wikispecieshas information related toLaridae.
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