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Seagull Close Up View
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Gulls or seagulls are seabirds of the family Laridae in the sub-order Lari. They are most closely related to the terns (family Sternidae) and only distantly related to auks, skimmers, and more distantly to the ,waders,Until the twenty-first century most gulls were placed in the genus Larus, but this arrangement is now known to be polyphyletic, leading to the resurrection of several genera.Gulls 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, stout, longish bills, and webbed feet. Most gulls, particularly Larus species, are ground-nesting carnivores, which will take live food or scavenge opportunistically. Live food often includes crabs and small fish. Gulls have prophylactic unhinging jaws which allow them to consume large prey. 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. Large White-Headed Gulls are typically long-lived birds, with a maximum age of 49 years recorded for the Herring Gull.
Gulls nest in large, densely packed 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 upon hatching. Gulls�the larger species in particular�are resourceful, inquisitive and 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. Certain species (e.g. the Herring Gull) have exhibited tool use behaviour, using pieces of bread as bait with which to catch goldfish, for example. 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. Gulls have been observed preying on live whales, landing on the whale as it surfaces to peck out pieces of flesh. 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). They are generally uniform in shape, with heavy bodies, long wings, moderately long necks . The tails of all but three species are rounded; the exceptions being the Sabine's Gull and Swallow-tailed Gulls, which have forked tails, and the Ross's Gull, which has a wedge-shaped tail. Gulls have moderately long legs (certainly longer than the 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. The gulls are generalist feeders, indeed 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 makings. The head of gulls may be covered by a dark hood or be entirely white. The plumage of the head varies by breeding season; in non-breeding dark-hooded gulls the hood is lost, sometimes leaving a single spot behind the eye, and in white-headed gulls non-breeding heads may have streaking.gulls have a worldwide cosmopolitan distribution. They breed on every continent, including the margins of Antarctica, and are found in the high Arctic as well. They are less common on tropical islands, although a few species do live on islands such as the Galapagos and New Caledonia. Many species breed in costal colonies, with a preference for islands, and one species, the Grey Gull, breeds in the interior of dry deserts far from water. There is considerable variety in the family and species may breed and feed in marine, freshwater or terrestrial habitats. Most gull species are migratory, with birds moving to warmer habitats during the winter, but the extent to which they migrate varies by species. Some species migrate long distances, like the Franklin's Gull, which migrates from Canada to wintering grounds in the south of South America. Other species move much shorter distances and may simply disperse along the coasts near their breeding sites Charadriiform birds drink salt water as well as fresh water, as they possess exocrine glands located in supraorbital grooves of the skull by which sodium chloride can be excreted through the nostrils to assist the kidneys in maintaining electrolyte balance.
Gulls are highly adaptable feeders that opportunistically take a wide range of prey. 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, plant items such as seeds and 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, and terrestrial prey such as seeds, fruit and earthworms are more common during the breeding season while marine prey is more common in the non-breeding season when birds spend more time on large bodies of water. In addition to taking a wide range prey items gulls display great versatility in how they obtain prey. Prey can be obtained in the air, on water or on land. In the air a number of hooded species are able to hawk insects on the wing; larger species perform this feat more rarely. Gulls on the wing will also snatch items both off water and off the ground, and over water they will also plunge-dive to catch prey. Again smaller species are more manoeuvrable and better able to hover-dip fish from the air. Dipping is also common when birds are sitting on the water, and gulls may swim in tight circles or foot paddle to bring marine invertebrates up to the surface. 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. In shallow water gulls may also engage in foot paddling. A unique method of obtaining prey to gulls involves dropping heavy shells of clams and mussels onto hard surfaces. Gulls may fly some distance in order to find a suitable surface on which to drop shells, and there is apparently a learnt component to the task as older birds are more successful than younger ones. While overall feeding success is a function of age, the diversity in both prey and feeding methods is not. It has been suggested that the time taken to learn foraging skills explains the delayed maturation in gulls.
Gulls have only a limited ability to dive below the water in order to feed on deeper prey. In order to obtain prey from deeper down many species of gull feed in association with other animals, where marine hunters drive prey to the surface when hunting. Examples of such associations include four species of gull feeding around plumes of mud brought to the surface by feeding Grey Whales, and also between Orcas(largest dolphin specie)and Kelp Gulls (and other seabirds)
May 31st, 2013
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