Gulls (often informally Seagulls) are birds in the family Laridae. They are most closely related to the terns (family Sternidae) and only distantly related to auks, and skimmers, and more distantly to the waders. Until recently, most gulls were placed in the genus Larus, but this arrangement is now known to be polyphyletic, leading to the resurrection of several genera.
They are typically medium to large birds, usually grey or white, often with black markings on the head or wings. They typically have harsh wailing or squawking calls. They have stout, longish bills, and webbed feet. Gull species range in size from the Little Gull, at 120 g (4.2 oz) and 29 cm (11.5 inches), to the Great Black-backed Gull, at 1.75 kg (3.8 lbs) and 76 cm (30 inches).
Most gulls, particularly Larus species, are ground nesting carnivores, which will take live food or scavenge opportunistically. The live food often includes crabs and small fish. Apart from the kittiwakes, gulls are typically coastal or inland species, rarely venturing far out to sea. The large species take up to four years to attain full adult plumage, but two years is typical for small gulls.
Gulls nest in large, densely packed, and noisy colonies. They lay two to three speckled eggs in nests composed of vegetation. The young are precocial, being born with dark mottled down, and mobile from birth.
Gulls—the larger species in particular—are resourceful and highly intelligent birds, demonstrating complex methods of communication and a highly developed social structure; for example, many gull colonies display mobbing behaviour, attacking and harassing would-be predators and other intruders. In addition, certain species (e.g. the Herring Gull) have exhibited tool use behaviour. Many species of gull have learned to coexist successfully with humans and have thrived in human habitats. Others rely on kleptoparasitism to get their food. The urban gull population in the United Kingdom has been growing quickly, probably due to laws such as the Clean Air Act 1956 which prohibited the burning of garbage by local landfill owners, thus increasing the availability of food for the gulls
The taxonomy of gulls is confused by their widespread distribution and geneflow leading to zones of hybridization. Some have traditionally been considered ring species, but recent evidence suggest this assumption is questionable. Until recently, most gulls were placed in the genus Larus, but this arrangement is now known to be polyphyletic, leading to the resurrection of the genera Ichthyaetus, Chroicocephalus, Leucophaeus, Saundersilarus and Hydrocoloeus. Some English names refer to species complexes within the group:
Hybridisation between species of gull occurs quite frequently, although to varying degrees depending on the species involved (see Hybridisation in gulls). The taxonomy of the large white-headed gulls is particularly complicated.
In common usage, members of various gull species are often referred to as sea gulls or seagulls. This name is used by the layman to refer to a common local species or all gulls in general, and has no fixed taxonomic meaning.
The Laridae are known from fossil evidence since the Early Oligocene, some 30-33 mya. A fossil gull from the Middle to Late Miocene of Cherry County, USA is placed in the prehistoric genus Gaviota; 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, "Larus" elegans and "L." totanoides from the Late Oligocene/Early Miocene of southeast France have since been separated in Laricola.