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Seabirds live longer, breed later and have fewer young than other birds do, but they invest a great deal of time in those young that they do have. Most species nest in colonies, which can vary in size from a few dozen birds to many millions. They 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 and Human s have a long history together, they have provided food to Hunter s, guided Fishermen to fishing stocks and Sailor s to land. Many species are currently Threatened by human activities, and Conservation efforts are underway to preserve them. CLASSIFICATION OF SPECIES AS SEABIRDS There exists no one 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''". Schreiber, Elizabeth A. & Burger, Joanne.(2001.) ''Biology of Marine Birds'', Boca Raton:CRC Press, ISBN 0-8493-9882-7 However by convention the Penguin s, Tubenose s, all the Pelecaniformes except the Darter s, and some of the Charadriiformes (the Skua s, Gull s, Tern s, Auk s and Skimmer s) are all considered seabirds. The Phalarope s are usually included as well, since although they are Wader s ("shorebirds" in North America ), two of the three species are oceanic for nine months of the year, crossing the equator to feed Pelagic ally. Loon s and Grebe s, which nest on lakes but winter at sea, are included by some authors, although they are usually treated as waterbirds. Although there are a number of Sea Duck s 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 Heron s are also highly marine, living on the sea's edge, but are also not treated as seabirds. EVOLUTION AND FOSSIL RECORD OF SEABIRDS Seabirds, by virtue of living in a Geologically depositional environment (that is, in the sea where Sediment s are readily laid down) are well represented in the Fossil record. They are first known to occur in the Cretaceous era, the earliest being the Hesperornithiformes , like ''Hesperornis regalis'', a flightless Loon -like seabird that dove in a similar fashion to loons and cormorants (using its feet to move underwater) but had a beak filled with sharp teeth. While ''Hesperornis'' is not thought to have left descendants, the earliest Extant seabirds also occurred in the Cretaceous, with a species called ''Tytthostonyx glauconiticus'', which has been placed in the Procellariiformes . In the Paleogene the seas were dominated by early Procellariidae , giant Penguin s and two Extinct Families , the Pelagornithidae and the Plotopteridae (a group of large seabirds that looked like the penguins). Modern genera began their wide radiation in the Miocene although the Genus '' Puffinus '' (which includes today's Manx Shearwater and Sooty Shearwater ) dates back to the Oligocene .Schreiber, Elizabeth A. & Burger, Joanne.(2001.) ''Biology of Marine Birds'', Boca Raton:CRC Press, ISBN 0-8493-9882-7 CHARACTERISTICS OF SEABIRDS Adaptations to life at sea Seabirds have made numerous adaptations to living on and feeding in the sea. Wing morphology has been shaped by the Niche an individual species or family has Evolved , so that looking at a wing's shape and Loading can tell a scientist about its life feeding behaviour. Longer wings and low wing loading are typical of more Pelagic species, whilst diving species have shorter wings. Species such as the Wandering Albatross , which forage over huge areas of sea, have a reduced capacity for powered flight and are dependent on a type of Gliding called Dynamic Soaring (where the wind deflected by waves provides lift) as well as slope soaring. Seabirds also almost always have webbed feet, both to aid movement on the surface as well as used for diving in some species. The Procellariiformes are also unusual amongst birds in having a strong sense of Smell (olfaction) which is used to find widely distributed food in a vast ocean,Lequette, B., Verheyden, C., Jowentin, P. (1989) "Olfaction in Subantarctic seabirds: Its phylogenetic and ecological significance" ''The Condor'' 91: 732-135. {Link without Title} and possibly to locate their colonies. Salt Gland s are used by seabirds to deal with the Salt they ingest by drinking and feeding (particularly on Crustacean s), and help them Osmoregulate . The Excretion s from these glands (positioned in the head of the birds and emerging from the Nasal Cavity ) are almost pure NaCl . With the exception of the Cormorant s, all seabirds have waterprooof Plumage in common with most other birds, however unlike terrestrial birds they have far more feathers protecting their bodies. This dense plumage is better able to protect the bird from getting wet, and cold is kept out by a dense layer of Down Feathers . The cormorants allow water to soak their feathers as it allows them to swim without fighting the Buoyancy that retaining air in the feathers causes, the cost of this is the need to dry out the feathers one they return to land. The plumage of most seabirds is less colourful than that of landbirds, mostly restricted to variations of black, white or grey. A few species sport colourful plumes (like the tropicbirds or some penguins), but the majority of colour in seabirds comes from the bills and legs. The plumage of seabirds is thought in many cases to be for Camouflage , both defensive (the colour of US Navy Battleship s is the same as that of Antarctic Prion s, in both cases it reduces visibility at sea), and aggressive (the white underside possessed by many seabirds helps hide them from prey below them). Seabird feeding Seabirds evolved to exploit different Food resources on the world's seas and oceans, and to a great extent their Physiology and Behaviour have been shaped by their Diet . These evolutionary forces have often caused species in different families and even orders to evolve similar strategies, and adaptations, to the same problems, leading to remarkable Convergent Evolution , such as that between Auk s and Penguin s. There are four basic feeding strategies, or ecological guilds, for at sea feeding, surface feeding, pursuit diving, plunge diving, and predation of higher vertebrates; within these guilds there are multiple variations on the theme. Surface feeding Many seabirds feed on the ocean's surface, as the action of marine Current s often concentrates food such as Krill , Fish , Squid or other prey items within reach of a dipped head. The distribution of prey on the sea's surface is often very patchy, some areas have large concentrations of food, while vast areas have none at all, so it is no coincidence that the species that exploit this resource are amongst the most efficient fliers of any of the seabirds, including the greatest long distance travelers of all, the Albatross es. Surface feeding itself can be broken up into two different approaches, surface feeding while Flying (for example as practiced by Gadfly Petrel s, Frigate-bird s and some Storm-petrel s) and surface feeding whilst swimming (examples of which are Fulmar s, Gull s, many Shearwater s and Gadfly Petrel s). Surface feeders in flight include some of the most acrobatic of seabirds, either snatching morsels from the water (as do frigate-birds and some terns), or 'walking' on the water's surface, as do the storm-petrels. Many of these do not land in the water and all and 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; Skimmer s fly 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. Surface feeders that swim often have unique bills as well, adapted for their specific prey. Prions have special bills with filters called Lamellae to filter out Plankton from mouthfulls of water,Brooke, M. (2004). ''Albatrosses And Petrels Across The World'' Oxford University Press, Oxford, UK ISBN 0-19-850125-0 and many albatross and petrels have hooked bills to snatch fast moving prey. Gulls have more generalised bills that reflect their more opportunistic lifestyle. Pursuit diving Pursuit diving exerts greater pressures (both evolutionary and physiological) on seabirds, but the reward is a greater area to feed in than is available to surface feeders. es holding the record at 12m.Prince, P.A., Huin, N., Weimerskirch, H., (1994) "Diving depths of albatrosses" ''Antarctic Science'' 6: (''3'') 353-354. Of all the wing-propelled pursuit divers, the most efficient in the air are the albatrosses, and it is no coincidence that they are the poorest divers. This is the dominant guild in polar and subpolar environments, as it is energetically inefficient in warmer waters. With their poor flying ability, many wing-propelled pursuit divers are more limited in their foraging range than other guilds, especially during the breeding season when hungry chicks need regular feeding. Plunge-diving s and Tuna to push shoaling fish up towards the surface. Au, D.W.K. & Pitman, R.L. (1986) Seabird interactions with Dolphins and Tuna in the Eastern Tropical Pacific. ''Condor'', 88: 304-317. {Link without Title} Kleptoparasitism, scavenging and other seabirds This catch-all category refers to other seabird strategies that involve the next Trophic Level up. Kleptoparasites are seabirds that make a living (or more often a part of their living) stealing food of other seabirds. Most famously Frigate-bird s and Skua s engage in this behaviour, although gulls, terns and other species will steal food opportunistically. The Nocturnal nesting behaviour of many seabirds has been interpreted as arising due to pressure from this arial piracy. Many species of gull will also feed on seabird and sea mammal Carrion when the opportunity arises, as will Giant Petrel s. Some species of albatross also engage in scavanging, an analysis of the regurgitated Squid beaks has shown that many of the squid eaten are too large to have been caught alive, and include mid-water species likely to be beyond the reach of albatross. Croxall, J.P. & Prince, P.A. (1994). "Dead or alive, night or day: how do albatrosses catch squid?" ''Antarctic Science'' 6: 155–162. Some species will also feed on other seabirds, for example gulls, skuas and giant petrels will often take eggs, chicks and even small seabirds on nesting colonies. Life-history Seabirds' life-histories are dramatically different from those of land birds. In general they are ), and many species (like the Tubenose s and Sulid s), only one egg a year. There is also a long period of care for the young, extending for as long as six months, among the longest for birds. For example, once Common Guillemot chicks fledge they remain with the male parent for several months at sea. This life-history strategy has probably evolved both in response to the challenges of living at sea and the relative lack of predation compared to that of land living birds. Because of the greater investment in raising the young and because foraging for food may occur far from the nest site, in most species both parents participate in caring for the young and pairs are typically at least seasonally monogamous. Seabird colonies :''See also Seabird Colony 95% of seabirds are colonial,Schreiber, Elizabeth A. & Burger, Joanne.(2001.) ''Biology of Marine Birds'', Boca Raton:CRC Press, ISBN 0-8493-9882-7 and seabird colonies are amongst the largest in the world, and provide one of Earth's great wildlife spectacles. Colonies of over a million birds have been recorded, both in the Tropic s (such as Kiritimati in the Pacific ) and in the polar latitudes (as found in Antarctica ). Seabird colonies occur exclusively for the purpose of breeding, non-breeding birds will only collect together outside the breeding season in areas where prey species are densely aggregated. Seabird colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed like a Murre colony. In most seabird colonies several different species will nest on the same colony, often exhibiting some Niche separation. Seabirds can nest in Tree s (if any are available), on the ground (with or without Nest s), on Cliff s, in burrows under the ground and in rocky crevices. Many seabirds show remarkable site Fidelity , returning to the same burrow, nest or site for many years, and they will defend that site from rivals with great vigour. This increases breeding success, provides an place for returning mates to reunite, and reduces the costs of prospecting for a new site. Young adults breeding for the first time usually return to their natal colony, and often nest very close to where they hatched. Colonies are thought to provide protection to seabirds, which are often very clumsy on land, and are usually situated on islands where land Mammal s have difficulty getting to. Coloniality often arises in other types of bird which do not defend feeding territories (such as Swift s, which have a very variable prey source), this may be a reason why it arises more frequently in seabirds. There are other possible advantages, colonies may act as information centres, where seabirds returning to the sea to forage can find out where prey is by studying returning individuals of the same species There are disadvantages to colonial life, particularly the spread of Disease . Colonies also attract the attention of Predator s, principally avian predators, and many species attend their colonies Nocturnally to avoid predation. Keitt, B.S., Tershy, B.R. & Croll, D.A (2004). "Nocturnal behavior reduces predation pressure on Black-vented Shearwaters Puffinus opisthomelas" ''Marine Ornithology'' 32 (3): 173-178. {Link without Title} Seabird migration 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 of Antarctica . Other species also undertake trans-equatorial trips, both from the north to the south, like Elegant Tern s, which nest off Baja California and feed off Peru in the Humboldt Current , or the two species of marine Phalarope s, the Grey Phalarope and the Red-necked Phalarope ; to those that undertake south to north, like the Sooty Shearwater s that nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific . Other species also migrate shorter distances away from the breeding sites, their distribution at sea determined by the availability of food. After Fledging , juvenile birds often disperse further than adults to, and to different areas, and are commonly sighted far from a species' normal range. Some species, such as the auks, do not have a concerted migration effort, but drift southwards as the winter approaches. Other species, such as some of the Storm-petrel s, Diving Petrel s and Cormorant s, never disperse at all, staying near the breeding colonies year round. Away from the sea Whilst the definition of seabirds suggests that the birds in question spend their lives on the like skuas and phalaropes, will migrate across land as well. The more marine species, such as Petrel s, Auk s, and Gannet s, are more restricted in their habits, but are occasionally seen inland as vagrants. This most commonly happens to young inexperienced birds, but can happen in large numbers to exhausted adults after a large Storm , an event known as a wreck, where they are prized sightings for Birder s. SEABIRDS AND HUMANS Seabirds and fisheries Seabirds have had a long association with both Fisheries and Sailor s. Both fisheries and seabirds have drawn benefits and disadvantages from the long relationship. Fishermen have long used seabirds as indicators of both fish s have been used to catch fish directly. Indirectly fisheries have also benefited from Guano from colonies of seabirds acting as Fertilizer for the surrounding seas. Negative effects on fisheries are mostly restricted to raiding by birds on Aquaculture , although Longlining fisheries also have to deal with Bait -stealing. There have been claims of prey-depletion by seabirds of fishery stocks, and while there is some small evidence of this, the effects of seabirds are considered smaller than that of Marine Mammal s and predatory fish (like Tuna ). Some species and families of seabirds have benefited from fisheries, particularly from discarded fish and s and Petrel s to the detriment of pursuit divers like Penguin s. Fisheries also have negative effects on seabirds, and these effects, particularly on the long lived and slow breeding are known to still exist). Seabirds also suffer when stocks of fish are overfished. Exploitation of seabirds The Hunting of seabirds, and the collecting of seabird Eggs , have contributed to the declines of many species of seabirds, as well as the Extinct ion of one species, the Great Auk . Seabirds have been hunted for food by many coastal people over time, and have become locally extinct in many places. In particular at least 20 species out of 29 no longer breed on Easter Island . In the 19th Century the hunting of seabirds for Fat deposits and feathers for the Millinery trade reached Industrial levels. In the Falkland Islands hundreds of thousands of penguins were harvested for their oil each year. Seabird eggs have also long been an important source of food for sailors undertaking long sea voyages, as well as being taken when cities grow in areas near a colony. Eggers from San Francisco took almost half a millions eggs a year from the Farallon Islands in the mid 19th century, a period in the island's history from which the seabird species are still recovering.White, Peter; ( 1995 ), The Farallon Islands, ''Sentinels of the Golden Gate'', Scottwall Associates:San Francisco, ISBN 0-942087-10-0 Both hunting and egging continue today, although not at the level that occurred in the past, and generally in a more controlled level. For example, the Māori of Stewart Island/Rakiura continue to harvest the chicks of the Sooty Shearwater as they have done so for centuries, using traditional methods (called kaitiakitanga) to manage the harvest, but now also work with the University Of Otago in studying the populations. In Greenland , however, uncontrolled hunting is pushing many species into steep decline.Burnham, W., Burnham, K.K., Cade, T.J., (2005) "Past and present assessments of bird life in Uummannaq District, West Greenland" ''Dansk Orn. Foren. Tidsskr.'' 99: 196-208 {Link without Title} Other threats Other human factors have led to declines and even extinctions in seabird populations, colonies and species. Of these, perhaps the most serious are s are capable of taking out seabirds as large as albatross, and many introduced rodents, such as the Pacific Rat can take eggs hidden in burrows. Introduced goats, cattle, rabbits and other herbivores can also lead to problems, particularly when species need vegetation to protect or shade their young. Disturbance of breeding colonies by people is often a problem as well, visitors, even well meaning Tourist s, can flush a colony leaving chicks and eggs vulnerable to predators. The build up of Toxin s and Pollutants in seabirds is also a concern. Seabirds, being apex predators, suffered from the ravages of DDT until they were banned, and concern continues with other pollutants, for example Forster's Tern s in San Francisco were found to have high levels of polybrominated diphenyl ethers (PBDEs), used as fire retardants. Oil Spill s are also a major threat to seabird species, as both a toxin and because the Feather s of the birds become saturated by the oil, causing them to lose their waterproofing. Seabird conservation The threats faced by seabirds have not gone unnoticed by scientists or the Conservation movement. As early as 1903 Theodore Roosevelt was convinced of the need to declare Pelican Island in Florida a National Wildlife Refuge to protect the bird colonies (including the nesting Brown Pelican s), a few years later in 1909 he protected the Farallon Islands . Today many important seabird colonies are given some measure of protection, from Heron Island in Australia to Triangle Island in British Columbia . The field of . The removal of these introduced species has led to increases in surviving species and even the return of expirated ones. After the removal of cats from Ascension Island seabirds began to nest there again for the first time in over a hundred years. Seabird mortality caused by long-line fisheries can be massively reduced by techniques such as setting long-line bait at night, dying the bait blue, setting the bait underwater, increasing the amount of weight on lines and using bird scarers can all reduce the seabird by-catch,Food and Agriculture Organisation (1999) "The incidental catch of seabirds by longline fisheries: worldwide review and technical guidelines for mitigation. FAO Fisheries Circular No.937. Food and Agriculture Organization of the United Nations, Rome. {Link without Title} and their deployment is increasingly required by many national fishing fleets. The international ban on the use of Drift Net s has also helped reduce the mortality of seabirds and other marine wildlife. One of the Millennium Projects in the UK was the Scottish Seabird Centre , near the important bird sanctuaries on Bass Rock , Fidra and other surrounding islands. The area is home to huge colonies of Gannet s, Puffins , skuas and other seabirds. The centre allows visitors to watch live video from the islands as well as learn about the threats the birds face and how we can protect them, and has helped to significantly raise the profile of seabird conservation in the UK. The plight of albatross and other large seabirds, as well as other marine creatures, being taken as by-catch by longline fisheries, has been taken up by a large number of NGOs (including BirdLife International and the RSPB ). This lead to Agreement On The Conservation Of Albatrosses And Petrels signed as part of the Convention On Migratory Species , a legally binding treaty designed to protect these threatened species (it has currently been ratified by eight countries, Argentina , Australia, Ecuador , New Zealand , Spain , France , Peru and South Africa . Seabirds in culture Many seabirds, living far out to sea and breeding in isolated colonies, have been and still are very obscure and unknown, even to scientists. Some seabirds have made the break into popular consciousness, most particularly the 's famous Poem , '' The Rime Of The Ancient Mariner '', where a sailor is punished for harming an albatross by wearing the dead bird around his neck. It was, however, considered unlucky to touch a Storm-petrel s, especially one that has landed on the ship. Gulls are one of the most commonly seen seabirds, given their use of human made Habitats (such as cities and dumps), and their often fearless nature. They therefore also have made it into the popular consciousness, if only as the 'flying rats' berated in '' Finding Nemo ''. They have been used Metaphorically , as in '' Jonathan Livingston Seagull '', by Richard Bach , or to denote a closeness to the Sea , such as their use in the Lord Of The Rings , both in the Insignia of Gondor , and therefore Númenor (used in the design of the film), and to call Legolas to, and across, the sea. SEABIRD FAMILIES The following are the groups of Bird s normally classed as seabirds. Sphenisciformes (Antarctic and southern waters; 16 species)
Procellariiformes (Tubenoses: pan-oceanic and pelagic; 93 species)
(see also Petrel ) Pelecaniformes (Worldwide; 57 species)
Charadriiformes (Worldwide; 305 species, but only the families listed are classed as seabirds.) For an alternative taxonomy of these groups, see also Sibley-Ahlquist Taxonomy . See also List Of Birds . REFERENCES
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