Gull - WikiHQ

thumb|right|Immature (probably 2nd year) [[Armenian gull in flight, flying over Lake Sevan]]

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. 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

thumb|left|upright=0.75|The [[Pacific gull is a large white-headed gull with a distinctively heavy bill.]]

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 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. Two species of gulls particularly dependent on human fisheries are Audouin's gull (Ichthyaetus audouinii) and lesser black-backed gulls (Larus fuscus); their breeding distributions (especially the black-backed gull) are heavily impacted by human fishing discards and fishing ports. Gulls in particular have high associations with salinity levels, which were found to be the main environmental predictor for waterbird assemblage.

Behaviour

Diet and feeding

thumb|left|[[Hartlaub's gull foot paddling, Cape Town]]

Like all Charadriiform birds, gulls can drink salt water, as well as fresh water, as they possess exocrine 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. Gulls are highly adaptable feeders that take a wide range of prey opportunistically. The food taken by gulls includes fish, and marine and freshwater invertebrates, both alive and already dead; terrestrial arthropods 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. or on wet grass for earthworms. One method of obtaining prey involves dropping heavy shells of clams and mussels onto hard surfaces. 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. and also between orcas (the largest dolphin species) and kelp gulls (among other seabirds).

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. This shift was linked to higher fishing efficiency and thus overall fish stock depletion. 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. Some gulls have been known to eat the eyeballs of baby seals, and directly pilfer milk from the teats of elephant seals.

Breeding

thumb|[[Black-legged kittiwakes nest colonially, but have tiny, closely packed territories.]]

thumb|The nest of a [[great black-backed gull, with three typical eggs]]

thumb|Two ring-billed gull chicks sitting amongst rocks

Gulls are monogamous and colonial 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 site 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 of band-tailed gulls 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 kittiwakes.

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 a day later; hatching is typically between 22 and 28 days, with little variation between species, the smallest only slightly shorter than the largest (little gull, 23–25 days; great black-backed gull, 27–28 days). 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. The taxonomy of gulls is confused by their widespread distribution zones of hybridisation leading to gene flow. Some have traditionally been considered ring species, but research has suggested that this assumption is questionable. Before the 21st century, 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:

Large white-headed gull is used to describe the 20 or so herring gull-like species in the genus Larus, from Ring-billed gull to Iceland gull in the taxonomic list below.
White-winged gull is used as a nickname for the two high Arctic-breeding species within the former group with no black in their wingtips; these are glaucous gull and Iceland gull. Mediterranean gull, in the genus Ichthyaetus, also has no black in the wingtips in adults and can be called "white-winged".

In common usage, members of various gull species are often referred to as 'seagulls' or 'sea gulls'; however, this is a layperson's term and often not used by 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. In common usage, gull-like seabirds that are not technically gulls (e.g. albatrosses, fulmars, terns, and skuas) may also be referred to as 'seagulls' by the layperson.

Early 21st century research usually treated the gulls as a distinct family Laridae separate from the terns in the family Sternidae. Subsequent research resulted in the merger of these two into just one family given uncertainty over the taxonomic status of the noddies, traditionally considered terns but seemingly basal in the whole group; a taxonomy that was followed by the IOC World Bird List for several years up to 2023. More comprehensive molecular phylogenetic analysis by Černý et al. in 2022 has however now shown that the noddies are basal only to the other terns, not the whole family; this was followed by the IOC World Bird List from version 14.1 in 2024. Despite this resolution of gulls and terns as separate monophyletic groups after all, they have remained placed together as subfamilies in a broad Laridae in the most recent Avilist classification.

The study published by Černý et al. found the following relationships between the genera, including the most recent generic change, the placement of Saunders's gull in its own genus Saundersilarus. 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.

References

External links

Rudy's Gull-index Pictures of less well-known plumages of large gulls