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Seabirds are Bird s 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 Paleogene . 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 Sailor s to land. Many species are currently Threatened by human activities, and Conservation efforts are under way. CLASSIFICATION OF SPECIES AS SEABIRDS 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 s and Procellariiformes , all of the Pelecaniformes except the Darter s, and some of the Charadriiformes (the Skua s, Gull s, Tern s, Auk s and Skimmer s) are classified as 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 pelagically. Loon s and Grebe s, which nest on lakes but winter at sea, are usually categorised as water birds, not seabirds. 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 (coast), but are also not treated as seabirds. EVOLUTION AND FOSSIL RECORD 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 Period, the earliest being the Hesperornithiformes , like ''Hesperornis regalis'', a flightless loon-like seabird that dove in a fashion similar to grebes and loons (using its feet to move underwater)Johansson LC, Lindhe Norberg UM. (2001) "Lift-based paddling in diving grebe." ''J Exp Biol.'' 204(10) :1687–96.[http://jeb.biologists.org/cgi/reprint/204/10/1687] but had a beak filled with sharp teeth.Gregory, J. (1952) "The Jaws of the Cretaceous Toothed Birds, Ichthyornis and Hesperornis" ''Condor'' '''54'''(2): 73–88 [http://elibrary.unm.edu/sora/Condor/files/issues/v054n02/p0073-p0088.pdf#search=%22The%20Jaws%20of%20the%20Cretaceous%20Toothed%20Birds%2C%20Ichthyornis%20and%20Hesperornis%20%22] While ''Hesperornis'' is not thought to have left descendants, the earliest . At the end of the latter, the oceanic Food Web had undergone a period of upheaval due to extinction of considerable numbers of marine species;Possibly due to comparatively close (in astronomical terms - c. 150 Light-year s) Supernova activity subsequently, the spread of marine mammals seems to have prevented seabirds from reaching their erstwhile diversity.Olson, S. & Hasegawa, Y. (1979)"Fossil Counterparts of Giant Penguins from the North Pacific" '' Science '' 206(4419): 688–689. CHARACTERISTICS Adaptations to life at sea Seabirds have made numerous adaptations to living on and feeding in the sea. are unusual amongst birds in having a strong Sense Of Smell , 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. s from these glands (which are positioned in the head of the birds, emerging from the Nasal Cavity ) are almost pure Sodium Chloride . With the exception of the that retaining air in the feathers causes, yet retain enough air to prevent the bird losing excessive heat through contact with water. The plumage of most seabirds is less colourful than that of land birds, restricted in the main to variations of black, white or grey. A few species sport colourful plumes (such as the tropicbirds or some penguins), but most of the colour in seabirds appears in 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, and in both cases it reduces visibility at sea) and aggressive (the white underside possessed by many seabirds helps hide them from prey below). Diet and feeding Seabirds evolved to exploit different Food resources in 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 feeding at sea: 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. s pattering on the water's surface]] Surface feeding itself can be broken up into two different approaches, surface feeding while , 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. Surface feeders that swim often have unique bills as well, adapted for their specific prey. Prion s have special bills with filters called Lamellae to filter out Plankton from mouthfuls of water,Brooke, M. (2004). ''Albatrosses And Petrels Across The World'' Oxford University Press, Oxford, UK ISBN 0-19-850125-0 and many albatrosses 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 in which to feed than is available to surface feeders. es, 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 predation This catch-all category refers to other seabird strategies that involve the next nesting behaviour of some seabirds has been interpreted as arising due to pressure from this aerial piracy.Gaston, A. J., and S. B. C. Dechesne. (1996). Rhinoceros Auklet (''Cerorhinca monocerata''). In ''The Birds of North America, No. 212'' (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, D.C. Kleptoparasitism is not thought to play a significant part of the diet of any species, and is instead a supplement to food obtained by hunting. A study of Great Frigatebird s stealing from Masked Boobies estimated that the frigatebirds could at most obtain 40% of the food they needed, and on average obtained only 5%.Vickery, J & Brooke, M. (1994) "The Kleptoparasitic Interactions between Great Frigatebirds and Masked Boobies on Henderson Island, South Pacific " ''Condor'' 96: 331–340 Many species of gull will feed on seabird and sea mammal 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 albatrosses.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 from nesting colonies.Punta, G, Herrera, G. (1995) "Predation by Southern Giant Petrels ''Macronectes giganteus'' on adult Imperial Cormorants ''Phalacrocorax atriceps''" ''Marine Ornithology'' '''23''' 166-167 {Link without Title} Life history Seabirds' life histories are dramatically different from those of land birds. In general, they are and Sulid s), only one egg a year. pair "billing" during courtship; like all seabirds except the phalaropes they maintain a pair bond throughout the breeding season.]] Care of young is protracted, 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. The Frigatebird s have the longest period of parental care of any bird, with the chicks fledging after four to six months and with continued assistance after that for up to fourteen months.Metz, V.G. & Schreiber, E.A. (2002) "Great Frigatebird (''Fregata minor'')" In ''The Birds of North America, No 681'', (Poole, A. & Gill, F., eds) The Birds of North America Inc:Philadelphia Due to the extended period of care, breeding occurs every two years rather than annually for some species. This life-history strategy has probably evolved both in response to the challenges of living at sea (collecting widely scattered prey items), the frequency of breeding failures due to unfavourable marine conditions, 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 all seabird species except the phalaropes, both parents participate in caring for the young, and pairs are typically at least seasonally Monogamous . Many species, such as gulls, auks and penguins, retain the same mate for several seasons, and many Petrel species mate for life. The albatrosses and Procellariid s which mate for life can take many years to form a pair bond before they breed, and the albatrosses have an elaborate breeding dance that is part of pair-bond formation.Pickering, S.P.C., & Berrow, S.D., (2001) "Courtship behaviour of the Wandering Albatross ''Diomedea exulans'' at Bird Island, South Georgia" ''Marine Ornithology'' 29: 29–37 {Link without Title} Breeding and colonies :''See also Seabird Colony s breed on densely packed colonies on offshore rocks, islands and cliffs.]] Ninety-five per cent of seabirds are colonial, and seabird colonies are amongst the largest bird colonies in the world, providing 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 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 as with 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 Burrow s under the ground and in rocky crevices. Competition can be strong both within species and between species, with aggressive species such as Sooty Tern s pushing less dominant species out of the most desirable nesting spaces.Schreiber, E. A., C. J. Feare, B. A. Harrington, B. G. Murray, Jr., W. B. Robertson, Jr., M. J. Robertson, and G. E. Woolfenden. 2002. Sooty Tern (''Sterna fuscata''). In ''The Birds of North America'', No. 665 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. The tropical Bonin Petrel nests during the winter to avoid competition with the more aggressive Wedge-tailed Shearwater . When the seasons overlap, the Wedge-tailed Shearwaters will kill young Bonin Petrels in order to use their burrows.Seto, N. W. H., and D. O'Daniel. (1999) Bonin Petrel (''Pterodroma hypoleuca''). In ''The Birds of North America, No. 385'' (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. Many seabirds show remarkable site s nesting near Corsica , found that of nine out of 61 male chicks that returned to breed at their natal colony bred in the burrow they were raised in, and two actually bred with their own mother.Rabouam, C., Thibault, J.-C., Bretagnole, V., (1998) "Natal Philopatry and Close Inbreeding in Cory's Shearwater (''Calonectris diomedea'')" ''Auk'' 115(2): 483–486 {Link without Title} Colonies are usually situated on islands, cliffs or headlands which land . Colonies also attract the attention of Predators , principally other birds, 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} Migration flock flying over Havana Bay area. These birds come to Cuba every year from North America in the north hemisphere winter season.]]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 Tern s, 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 .Burness, G. P., K. Lefevre, and C. T. Collins. 1999. Elegant Tern (''Sterna elegans''). In ''The Birds of North America'', No. 404 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. 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 Mile s (64,000 km).Shaffer S.A., Tremblay Y., Weimerskirch H., Scott D., Thompson D.R., Sagar P.M., Moller H., Taylor G.A., Foley D.G., Block B.A., Costa D.P. (2006) "Migratory shearwaters integrate oceanic resources across the Pacific Ocean in an endless summer." ''Proc Natl Acad Sci.'' '''103'''(34): 12799–12802 Other species also migrate shorter distances away from the breeding sites, their distribution at sea determined by the availability of food. If oceanic conditions are unsuitable, seabirds will emigrate to more productive areas, sometimes permanently if the bird is young.Oro, D., Cam, E., Pradel, R. & Martinetz-Abrain, A. (2004) "Influence of food availability on demography and local population dynamics in a long-lived seabird" ''Proc. R. Soc. London B.'' 271:387–396 After fledging, juvenile birds often disperse further than adults, and to different areas, so 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 their breeding colonies year round. Away from the sea While the definition of seabirds suggests that the birds in question spend their lives on the ocean, many seabird families have many species that spend some or even most of their lives inland away from the sea. Most strikingly, many species breed many tens, hundreds or even thousands of miles inland. Some of these species still return to the ocean to feed; for example, the -like skuas and phalaropes, will migrate over land as well. The more marine species, such as . RELATIONSHIP WITH HUMANS Seabirds and fisheries Seabirds have had a long association with both Fisheries and Sailor s, and both have drawn benefits and disadvantages from the relationship. Fishermen have traditionally used seabirds as indicators of both fish that might indicate fish stocks, and of potential landfall. In fact, the known association of seabirds with land was instrumental in allowing the Polynesia ns to locate tiny landmasses in the Pacific. Seabirds have provided food for fishermen away from home, as well as bait. Famously, tethered Cormorant 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 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 evidence of this, the effects of seabirds are considered smaller than that of Marine Mammal s and predatory fish (like Tuna ). Some seabird species have benefited from fisheries, particularly from discarded fish and through the British Isles is attributed in part to the availability of discards.Thompson, P.M., (2004) "Identifying drivers of change; did fisheries play a role in the spread of North Atlantic fulmars?" in '' Management of marine ecosystems: monitoring change in upper trophic levels''. Cambridge: Cambridge University Press {Link without Title} Discards generally benefit surface feeders, such as gannets and petrels, to the detriment of pursuit divers like penguins. Fisheries also have negative effects on seabirds, and these effects, particularly on the long-lived and slow-breeding albatrosses, are a source of increasing concern to conservationists. The bycatch of seabirds entangled in nets or hooked on fishing lines has had a big impact on seabird numbers; for example, an estimated 100,000 albatrosses are hooked and drown each year on tuna lines set out by long-line fisheries.BirdLife International/RSPB (2005) Save the Albatross: The Problem Retrieved es are known to still exist). Seabirds are also thought to suffer when overfishing occurs. Exploitation The , 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 settlements grow in areas near a colony. Eggers from San Francisco took almost half a million eggs a year from the Farallon Islands in the mid-19th century, a period in the islands' 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 levels that occurred in the past, and generally in a more controlled manner. For example, the Māori of Stewart Island/Rakiura continue to harvest the chicks of the Sooty Shearwater as they have done for centuries, using traditional methods (called '' Kaitiakitanga '') to manage the harvest, but now 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 , can flush brooding adults off a colony leaving chicks and eggs vulnerable to predators. spill of 2004.]] The build-up of s are also a threat to seabird species, as both a toxin and because the feathers of the birds become saturated by the oil, causing them to lose their waterproofing.Dunnet, G., Crisp, D., Conan, G., Bourne, W. (1982) "Oil Pollution and Seabird Populations Discussion " ''Philosophical Transactions of the Royal Society of London. B'' 297(1087): 413–427 Oil pollution threatens species with restricted ranges or already depressed populations. Conservation The threats faced by seabirds have not gone unnoticed by scientists or the . Today many important seabird colonies are given some measure of protection, from Heron Island in Australia to Triangle Island in British Columbia . . The removal of these introduced species has led to increases in numbers of species under pressure and even the return of extirpated ones. After the removal of cats from Ascension Island, seabirds began to nest there again for the first time in over a hundred years.BirdLife International (2005) Stamps celebrate seabird return . Retrieved August 12 2006 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 by using bird scarers,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 the surrounding islands. The area is home to huge colonies of gannets, Puffin s, 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. Seabird tourism can provide income for coastal communities as well as raise the profile of seabird conservation. For example, the Northern Royal Albatross colony at Taiaroa Head in New Zealand attracts 40,000 visitors a year. The plight of albatross and large seabirds, as well as other marine creatures, being taken as bycatch by long-line fisheries, has been addressed by a large number of Non-governmental Organization s (including BirdLife International and the Royal Society For The Protection Of Birds ). This led to the Agreement On The Conservation Of Albatrosses And Petrels , a legally binding treaty designed to protect these threatened species, which has been ratified by eight countries as of 2006 (namely Australia, Ecuador , France , New Zealand, Peru , South Africa , Spain , and the United Kingdom ).Australian Antarctic Division Agreement on the Conservation of Albatrosses and Petrels Site Retrieved September 2 2006 Role in culture , Kent .]] 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",Carboneras, C. (1992) "Family Diomedeidae (Albatrosses)" in ''Handbook of Birds of the World'' Vol 1. Barcelona:Lynx Edicions, ISBN 84-87334-10-5 and have a variety of '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. ''Instead of the Cross the Albatross'' ''About my neck was hung'' Sailors did, however, consider it unlucky to touch a Storm-petrel , especially one that has landed on the ship.Carboneras, C. (1992) "Family Hydrobatidae (Storm-petrels)" in ''Handbook of Birds of the World'' Vol 1. Barcelona:Lynx Edicions, ISBN 84-87334-10-5 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 - they have been used Metaphor ically, as in '' Jonathan Livingston Seagull '' by Richard Bach , or to denote a closeness to the sea, such as their use in the '' The Lord Of The Rings '' – both in the Insignia of Gondor and therefore Númenor (used in the design of the films), and to call Legolas to (and across) the sea. Other species have also made an impact; Pelican s have long been associated with mercy and Altruism because of an early Western Christian myth that they split open their breast to feed their starving chicks. SEABIRD FAMILIES The following are the groups of birds normally classed as seabirds. Sphenisciformes (Antarctic and southern waters; 16 species)
Procellariiformes (Tubenoses: pan-oceanic and pelagic; 93 species)
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 EXTERNAL LINKS
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