Gulls, or colloquially seagulls, are of the subfamily Larinae. They are most closely related to and skimmers, distantly related to , and even more distantly related to . Until the 21st century, most gulls were placed in the genus Larus, but that arrangement is now considered polyphyletic, leading to the resurrection of several genera.[ An older name for gulls is mews; this still exists in certain regional English dialects and is cognate with German Möwe, Danish måge, Swedish mås, Dutch meeuw, Norwegian måke/måse, and French mouette.]
Gulls are usually grey or white, often with black markings on the head or wings. They normally have harsh wailing or squawking calls, stout bills, and webbed feet. Most gulls are ground-nesting or which take live food or scavenge opportunistically, particularly the Larus species. Live food often includes , , 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 the and Sabine's gull.
Gulls nest in large, densely packed, noisy colonies. They lay two or three speckled eggs in nests composed of vegetation. The young are precocial, born with dark mottled down and mobile upon hatching.[Alcock, J. (1998). Animal Behavior: An Evolutionary Approach (7th edition). Sinauer Associates, Inc. Sunderland, Massachusetts. .] Certain species, such as the herring gull, have exhibited tool-use behaviour, for example using pieces of bread as bait with which to catch goldfish.
Description and morphology
Gulls range in size from the little gull, at and , to the great black-backed gull, at and . 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 being Sabine's gull and swallow-tailed gulls, which have forked tails, and Ross'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.
Gulls are a generalist 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.
The general pattern of plumage 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, the ivory gull is entirely white, and some like the lava gull and Heermann'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.
Distribution and habitat
Gulls have a worldwide cosmopolitan distribution. They breed on every continent, including the margins of Antarctica, and are even found in the high Arctic. They are less common in the tropics, although a few species do live on tropical islands such as the Galapagos and New Caledonia. Many species breed in coastal colonies, with a preference for islands; one particular species, the grey gull, breeds in the interior of dry deserts far from water. Considerable variety exists in the Laridae family, and species may breed and feed in marine, freshwater, or terrestrial habitats.
Most gull species are Bird migration, with birds moving to warmer habitats during the winter, but the extent to which they migrate varies by species. Some migrate long distances, notably Sabine's gull, which migrates from the Arctic coasts to wintering grounds off the west coasts of South America and southern Africa, and Franklin'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.
Other environmental drivers that structure bird habitat and distribution are human activity and climate impacts. For example, waterbird distribution in Mediterranean is influenced by changes in salinity, water depth, water body isolation and , all of which have been observed to affect the bird community structure in both a species- and guild-specific way.
Behaviour
Diet and feeding
Charadriiform birds drink salt water, as well as fresh water, as they possess located in supraorbital grooves of the skull by which salt can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance.
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
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.
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.
Breeding
Gulls are monogamous and Seabird colony 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 of Philopatry, 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 of may breed in colonies of other bird species. Within colonies, gull pairs are territorial, defending an area of varying size around the nesting site from others of their species. This area can be as large as a radius around the nest in the European herring gull to just a tiny area of cliff ledge in the .
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 their , 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.
Nest building is an important part of the pair-bonding process. Most gull nests are mats of 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 in . Both sexes gather nesting material and build the nest, but the division of labour is not always exactly equal.
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 sexes Egg incubation the eggs; incubation bouts last between one and four hours during the day, and one parent incubates through the night.
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 they fledge. 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.
Taxonomy
The family Laridae was introduced (as Laridia) by the French polymath Constantine Samuel Rafinesque in 1815.
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Large white-headed gull is used to describe the 18 or so herring gull-like species, from California gull to lesser black-backed gull in the taxonomic list below.
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White-winged gull is used to describe the four pale-winged, high Arctic-breeding taxa within the former group; these are Iceland gull, glaucous gull, Thayer's gull, and Kumlien's gull.
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.
The American Ornithologists' Union combines the Sternidae, Stercorariidae, and Rhynchopidae as Subfamily in the family Laridae, but early 21st-century research
A molecular 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 genus Saundersilarus.
List of species
This is a list of the 54 gull species, presented in taxonomic sequence.
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| | Larus |
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Pacific gull Larus pacificus
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Belcher's gull Larus belcheri
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Olrog's gull Larus atlanticus
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Black-tailed gull Larus crassirostris
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Heermann's gull Larus heermanni
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Common gull Larus canus
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Short-billed gull Larus brachyrhynchus
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Ring-billed gull Larus delawarensis
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California gull Larus californicus
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Great black-backed gull Larus marinus
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Kelp gull Larus dominicanus ("southern black-backed gull" or " karoro" in New Zealand)
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Cape gull Larus dominicanus vetula
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Glaucous-winged gull Larus glaucescens
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Western gull Larus occidentalis
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Yellow-footed gull Larus livens
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Glaucous gull Larus hyperboreus
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Iceland gull Larus glaucoides
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Kumlien's gull Larus glaucoides kumlieni
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Thayer's gull Larus glaucoides thayeri
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European herring gull Larus argentatus
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American herring gull Larus smithsonianus
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Caspian gull Larus cachinnans
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Yellow-legged gull Larus michahellis
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Vega gull Larus vegae
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Armenian gull Larus armenicus
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Slaty-backed gull Larus schistisagus
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Lesser black-backed gull Larus fuscus
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Heuglin's gull Larus fuscus heuglini
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| | Ichthyaetus |
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White-eyed gull Ichthyaetus leucophthalmus
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Sooty gull Ichthyaetus hemprichii
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Pallas's gull (or Great black-headed gull) Ichthyaetus ichthyaetus
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Audouin's gull Ichthyaetus audouinii
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Mediterranean gull Ichthyaetus melanocephalus
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Relict gull Ichthyaetus relictus
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| | Leucophaeus | |
| | Chroicocephalus |
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Silver gull Chroicocephalus novaehollandiae
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Huahine gull Chroicocephalus utunui (extinct)
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Hartlaub's gull Chroicocephalus hartlaubii
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Brown-hooded gull Chroicocephalus maculipennis
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Grey-headed gull Chroicocephalus cirrocephalus
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Andean gull Chroicocephalus serranus
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Black-billed gull Chroicocephalus bulleri
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Brown-headed gull Chroicocephalus brunnicephalus
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Black-headed gull Chroicocephalus ridibundus
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Slender-billed gull Chroicocephalus genei
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Bonaparte's gull Chroicocephalus philadelphia
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| | Saundersilarus |
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Saunders's gull, Saundersilarus saundersi
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| | Hydrocoloeus (may include Rhodostethia) | |
| | Rhodostethia |
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Ross's gull Rhodostethia rosea
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| | Kittiwake |
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Black-legged kittiwake Rissa tridactyla
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Red-legged kittiwake Rissa brevirostris
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| | Pagophila | |
| | Xema |
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Sabine's gull Xema sabini
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| | Creagrus |
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Swallow-tailed gull Creagrus furcatus
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Evolutionary history
The Laridae are known from not-yet-published fossil evidence since the Early Oligocene, some 30–33 million years ago. Three gull-like species were described by Alphonse Milne-Edwards from the early Miocene of Saint-Gérand-le-Puy, France. A fossil gull from the Middle Miocene to Late Miocene of Cherry County, Nebraska, US, is placed in the prehistoric genus Gaviota;[Miller, A. H. and Sibley (1941) described Gaviota niobrara from the upper Miocene of Nebraska] apart from this and the undescribed Early Oligocene fossil, all prehistoric species were tentatively assigned to the modern genus Larus. Among those of them that have been confirmed as gulls, Milne-Edwards' "Larus" elegans and "L." totanoides from the Late Oligocene/Early Miocene of southeast France have since been separated in Laricola.
Further reading
External links
