Gulls, informally called seagulls (see Taxonomy), are seabirds of the subfamily Larinae. They are most closely related to terns and skimmers, and are placed with them in the family Laridae. They are also related, more distantly, to auks and skuas, and more distantly still to waders. Until the 21st century, most gulls were placed in the genus Larus, but that arrangement is now considered polyphyletic, leading to the readoption and revision of several genera. An older name for gulls is mew; 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; both 'gull' and 'mew' are ultimately onomatopoeic in origin, derived from the calls of the birds. Gulls are usually grey and white, often with black markings on the head or wings, strong bills, and all have webbed feet. They normally have harsh mewing, wailing or squawking calls. Most gulls are ground-nesting piscivores or carnivores which take live food or scavenge opportunistically, particularly the larger species in the genus Larus. Live food includes crustaceans, molluscs, fish, and for the larger species, birds and mammals. Gulls' jaws can unhinge to allow them to consume large prey. They are typically coastal or inshore (or even inland) species, rarely venturing far out to sea, except the kittiwakes and Sabine's gull. 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 the European herring gull. Gulls nest in large, often 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. Gulls are resourceful, inquisitive, and intelligent, the larger species in particular, demonstrating complex methods of communication and a highly developed social structure. For example, many gull colonies display mobbing behaviour, attacking and harassing predators and other intruders. 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. Many species of gulls have learned to coexist successfully with humans and thrive in human habitats. Others rely on kleptoparasitism 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.
Description and morphology
Gulls range in size from the little gull, at 120 grams (4+1⁄4 ounces) and 29 centimetres (11+1⁄2 inches), to the great 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 being Sabine's gull and swallow-tailed gull, 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 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 on or near the primary feather tips. The head of a gull may be covered by a dark hood or be entirely white. The plumage of the head varies between breeding and non-breeding seasons. In dark-hooded gulls, the hood is lost out of the breeding season, usually leaving a diffuse dark spot or mask through or behind the eye; in white-headed gulls, nonbreeding heads often have dark streaking on the head and neck.
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. Many gull species are migratory, 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.
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