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A seabird is a bird that spends most of its time at sea. Seabirds gather their food from the sea either by themselves or in large feeding flocks.
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations. The first seabirds evolved in the Cretaceous period, and modern seabird families emerged in the Palaeogene.
In general, seabirds live longer, breed later and have fewer young than other birds do, but they invest a great deal of time in their young. Most species nest in colonies, which can vary in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even feed on each other. Seabirds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely.
Seabirds and humans have a long history together: they have provided food to hunters, guided fishermen to fishing stocks and led sailors to land. Many species are currently threatened by human activities, and conservation efforts are under way.
There exists no single definition of which groups, families, and species are seabirds, and most definitions are in some way arbitrary. In the words of two seabird scientists, "The one common characteristic that all seabirds share is that they feed in saltwater; but, as seems to be true with any statement in biology, some do not." However, by convention all of the penguins and Procellariiformes, all of the Pelecaniformes except the darters, and some of the Charadriiformes (the skuas, gulls, terns, auks and skimmers) are classified as seabirds. The phalaropes are usually included as well, since although they are waders ("shorebirds" in North America), two of the three species are oceanic for nine months of the year, crossing the equator to feed pelagically.
Loons and grebes, which nest on lakes but winter at sea, are usually categorized as water birds, not seabirds. Although there are a number of sea ducks in the family Anatidae which are truly marine in the winter, by convention they are usually excluded from the seabird grouping. Many waders (or shorebirds) and herons are also highly marine, living on the sea's edge (coast), but are also not treated as seabirds.
Many seabirds feed on the ocean's surface, as the action of marine currents often concentrates food such as krill, fish, squid or other prey items within reach of a dipped head.
Surface feeding itself can be broken up into two different approaches, surface feeding while flying (for example as practiced by gadfly petrels, frigatebirds and storm-petrels), and surface feeding whilst swimming (examples of which are practiced by fulmars, gulls, many of the shearwaters and gadfly petrels). Surface feeders in flight include some of the most acrobatic of seabirds, which either snatch morsels from the water (as do frigate-birds and some terns), or "walk", pattering and hovering on the water's surface, as some of the storm-petrels do. Many of these do not ever land in the water, and some, such as the frigatebirds, have difficulty getting airborne again should they do so. Another seabird family that does not land while feeding is the skimmer, which has a unique fishing method: flying along the surface with the lower mandible in the water—this shuts automatically when the bill touches something in the water. The skimmer's bill reflects its unusual lifestyle, with the lower mandible uniquely being longer than the upper one.
Like many birds, seabirds often migrate after the breeding season. Of these, the trip taken by the Arctic Tern is the farthest of any bird, crossing the equator in order to spend the Austral summer in Antarctica. Other species also undertake trans-equatorial trips, both from the north to the south, and from south to north. The population of Elegant Terns, which nest off Baja California, splits after the breeding season with some birds travelling north to the Central Coast of California and some travelling as far south as Peru and Chile to feed in the Humboldt Current. The Sooty Shearwater undertakes an annual migration cycle that rivals that of the Arctic Tern; birds that nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 40,000 statute miles (64,000 km).
Many seabirds are little studied and poorly known, due to living far out to sea and breeding in isolated colonies. However, some seabirds, particularly, the albatrosses and gulls, have broken into popular consciousness. The albatrosses have been described as "the most legendary of birds", and have a variety of myths and legends associated with them, and today it is widely considered unlucky to harm them, although the notion that sailors believed that is a myth which derives from Samuel Taylor Coleridge's famous poem, "The Rime of the Ancient Mariner", in which a sailor is punished for killing an albatross by having to wear its corpse around his neck.
The Common Guillemot or Common Murre (Uria aalge) is a large auk. It is also known as the Thin-billed Murre in North America. It has a circumpolar distribution, occurring in low-Arctic and boreal waters in the North-Atlantic and North Pacific. It spends most of its time at sea, only coming to land to breed on rocky cliff shores or islands.Common Guillemots breed in colonies at high densities, nesting pairs may be in bodily contact with their neighbours. They make no nest, their single egg is incubated on bare rock. Eggs hatch after ~30 days incubation. The chick is born downy, and can regulate its body temperature after 10 days. They leave the nest site in around 20 days accompanied by the male parent. Chicks cannot fly when they leave the nest but are capable of diving as soon as they hit the water. The female stays at the nest site about 14 days after the chick has left.
The Common Guillemot can venture far from its breeding grounds to forage; distances of 100 km and more are often observed though if sufficient food is available closer by, birds only travel much shorter distances. The Common Guillemot mainly eats small schooling fish 200 mm long or less, such as polar cod, capelin, sand lances, sprats, sandeels, Atlantic cod and Atlantic herring. Capelin and sand lances are favourite food, but what the main prey is at any one time depends much on what is available in quantity. It also eats some molluscs, marine worms, squid, and crustaceans such as amphipods. It consumes 20-32 grams of food in a day on average. It is often seen carrying fish in its bill with the tail hanging out
Common Guillemot eggs are large (around 11% of female weight), and are pointed at one end. There are a few theories to explain their pyriform shape:
In areas such as Newfoundland, the birds, along with the related Brunnich's Guillemot, are referred to as 'turrs' or 'tuirs', and are consumed. The meat is dark and quite oily, due to the birds' diet of fish. Eggs have also been harvested. Eggers from San Francisco took almost half a million eggs a year from the Farallon Islands in the mid-19th century to feed the growing city.
The Parakeet Auklet is a small seabird of the North Pacific. It used to be placed on its own in the genus Cyclorrhynchus (Kaup, 1829) but recent morphological and genetic evidence suggest it should be placed in the genus Aethia. It is associated with the boreal waters of Alaska and Kamchatka and Siberia. It breeds on the cliffs, slopes and boulder fields of offshore islands, generally moving south during the winter.
The Parakeet Auklet is a small (23 cm) auk with a short orange bill that is upturned to give the bird its curious fixed expression. The bird's plumage is dark above and white below. with a single white plume projecting back from the eye. There is a small amount of variation between breeding and winter plumage. The Parakeet Auklet's food varies with season, during the breeding season it takes mostly small planktonic crustaceans such as euphausiids, copepods and amphipods. Recent research shows it also preys on jellyfish in some areas. It often feeds at a considerable distance from the colony, diving up to 30 m to reach its prey.
The Parakeet Auklet is not considered threatened, there are estimated to be over a million individuals in the North Pacific. It is not thought to have declined recently, but may be threatened in the future by introduced predators and oil spills.
The Double-crested Cormorant (Phalacrocorax auritus) is a member of the cormorant family of seabirds. It occurs along inland waterways as well as in coastal areas, and is widely distributed across North America, from the Aleutian Islands in Alaska down to Florida and Mexico. Measuring 70–90 cm (28–35 in) in length, it is an all-black bird which gains a small double crest of black and white feathers in breeding season. It has a bare patch of orange-yellow facial skin. Five subspecies are recognized.
The Double-crested Cormorant is a large waterbird with a stocky body, long neck, medium-sized tail, webbed feet and a medium sized hooked bill. It has a body length of between 70–90 cm (28–35 in) long, with a wingspan of between 114–132 cm (45–52 in).[12][13] Double-crested Cormorants weigh between 1200–2500 g (42.36–88.25 ounces) Males and females do not display sexual dimorphism. A very common and widespread species, it winters anywhere that is ice-free along both coasts, as far north as southern Alaska (on the west coast) and southern New England (on the east coast). It can be found as far south as Mexico and the Bahamas. It migrates from the coldest parts of its breeding range, such as eastern Canada, and has occurred in Europe as a very rare vagrant, for example in Great Britain, Ireland and the Azores.
The Double-crested Cormorant swims low in the water, often with just its neck and head visible, and dives from the surface. It uses its feet for propulsion and is able to dive to a depth of 1.5–7.5 m (5–25 feet) for 30–70 seconds. After diving, it spends long periods standing with its wings outstretched to allow them to dry, since they are not fully waterproofed. This species flies low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single-file lines.Breeding occurs in coastal areas as well as near inland rivers and lakes. They build stick nests in trees, on cliff edges, or on the ground on suitable islands. They are gregarious birds usually found in colonies, often with other aquatic birds, and have a deep, guttural grunt call.
The Northern Fulmar (Fulmarus glacialis), or Arctic Fulmar lives in the north Atlantic and north Pacific. These fulmars look superficially like gulls, but are unrelated, and are in fact petrels. The species is grey and white with a yellow bill, 43-52 cm in length with a 101-117 cm wingspan. The Northern Fulmar has both a light morph and dark morph plumage.
They are highly pelagic outside the breeding season, like most tubenoses, feeding on fish, oil or offal. Recent studies in the North Sea have shown them especially susceptible to plastic discards. The range of these species increased greatly last century due to the availability of fish offal from commercial fleets, but may contract because of less food from this source and climatic change. The population increase has been especially notable in the British Isles.
Like other petrels, their walking ability is limited, but they are strong fliers, with a stiff wing action quite unlike the gulls. They look bull-necked compared to gulls, and have short stubby bills. They are long-lived, with a lifespan of 40 years not uncommon. The Sibley-Ahlquist taxonomy gives a radically different scientific arrangement for this group based on DNA studies.
The Short-tailed Albatross or Steller's Albatross, Phoebastria albatrus, is a large rare seabird from the North Pacific. Although related to the other North Pacific albatrosses, it also exhibits behavioural and morphological links to the albatrosses of the Southern Ocean. It was described by the German naturalist Peter Simon Pallas from skins collected by the intrepid Georg Wilhelm Steller (after whom its other common name is derived). Once common, it was brought to the edge of extinction by the trade in feathers, but with protection has recently made a recovery.
The Short-tailed Albatross is a medium sized albatross, with a wingspan of 215–230 cm (85–91 in), a length of 84–94 cm (33–37 in) and a body weight of about 4.3–8.5 kg (9.5–19 lb). Its plumage as an adult is overall white with black flight feathers, some coverts, as well as a black terminal bar on its tail. It has a yellow-stained nape and crown. Its bill is large and pink; however, older birds will gain a blue tip.
Short-tailed Albatrosses now nest on only two islands, with the majority of birds nesting on Torishima, and the remainder nesting on Minami-kojima in the Senkaku Islands. During non-breeding season they range across the North Pacific, with the males and juveniles gathering in the Bering Sea, and the females feeding off the coast of Japan and eastern Russia. They can also be found as far east as California. In fact, the Short-tailed Albatross is seen on a number of the United States' state endangered species lists including Washington State.
The Short-tailed Albatross came perilously close to extinction. They were hunted on an almost industrial scale for their feathers in the later half of the 19th century with some estimates claiming upward of 10 million birds hunted. By the 1930s the only population left was on Torishima, between 1927 and until 1933 hunting continued when the Japanese government declared the ban of hunting to save the species, after which the albatrosses stopped breeding on the island. At this point the species was assumed to be extinct and research became impossible with the outbreak of World War II. On 1949 an American researcher arriving on this island declared the species to be extinct, but an estimated 50 individuals, most likely juveniles, survived at sea (all albatross species take a long time to reach sexual maturity and will not return to their natal colony for many years). After the return of the birds they were more carefully protected, and the first egg was laid by the returning birds in 1954. Varieties of albatross decoys were placed around on the island after it was discovered that like other albatross species, this species also were enticed to breed if placed in a group.