Gull

Gull, common name for approximately 47 species of long-winged, web-footed seabirds, the most familiar birds of the seashore. The commonly used name sea gull is a misnomer. Many species nest or feed inland, and most of the rest are strictly coastal; only the kittiwakes are truly oceanic during the nonbreeding season. Gulls are distributed worldwide, excluding only tropical deserts and jungles, the central Pacific islands, and most of Antarctica. Some gulls are migratory.

CHARACTERISTICS
Gull sizes, from bill to tail, range from 27 to 80 cm (11 to 31 in). The bill is hooked. Except for the totally white ivory gull, the birds vary from pale gray to black above, and from white to gray below. The heads of many have black, gray, or dark brown hoods during breeding season. Many of the gray-winged species have black or darker gray wing tips, often with white spots. The sexes are alike in color. The young have mottled brown or gray plumage, taking as long as four years (in the larger species) to attain the definitive adult coloration through a progressive series of annual molts.

Gulls are equipped for versatility rather than specialization. For example, their wings are good for soaring as well as for strong and agile powered flight, but they cannot use air currents as efficiently as albatrosses or fly as fast as falcons. The foraging of gulls includes fishing, scavenging, egg predation, insect catching, following plows for earthworms and ships for garbage, dropping shellfish from a height to break them open, and foot paddling to stir up organisms in shallow water.

LIFE CYCLE
Gulls breed colonially, mostly on the flat ground of beaches, marshes, or riverbeds, where they build simple, shallow, grass-lined nests. Several species nest on ledges of cliffs, notably the kittiwakes. The clutch consists of two or three greenish-brown, speckled eggs, which take 20 to 30 days to incubate. At hatching the chicks have down feathers, and the eyes are open. Chicks can stand but are dependent on their parents for food and warmth. The parents share in incubation of the eggs and in the brooding and feeding (by regurgitation) of the chicks, which fledge between four and six weeks after hatching. Gulls have been known to live as long as 40 years in captivity and as long as 36 years in the wild.

BEHAVIOR
Territory defense, pair formation, parent-chick interactions, and other gull activities involve communication behavior consisting of postures, movements, and calls, some of which are quite complex both in form and in function. For example, courting gulls perform threat displays, but they do so in sequences that apparently modify the meaning of the display. Recognition of one individual by another by such means has been demonstrated experimentally. Pair bonds may be long lasting.

Gulls may thrive at the expense of other species. For example, larger gulls are known to drive out smaller gulls and terns from nesting territories, partly through egg and chick predation. The scavenging of gulls can also affect the ecology of urban environments. Airfields (and the garbage dumps that are commonly located near them) attract large numbers of gulls, which present a collision hazard to aircraft; this problem has yet to be solved. In some places, gulls' eggs are collected for food.

Scientific classification: Gulls belong to the family Laridae in the order Charadriiformes.

Contributed By:
Colin G. Beer

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