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Seabirds (also known asmarine birds) arebirds that areadapted to life within themarine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit strikingconvergent evolution, as the same environmental problems and feedingniches have resulted in similar adaptations. The first seabirds evolved in theCretaceousperiod, while modern seabird families emerged in thePaleogene.
Seabirds generally live longer,breed later and have fewer young than other birds, but they invest a great deal of time in their young. Mostspecies nest incolonies, varying in size from a few dozen birds to millions. Many species are famous for undertaking long annualmigrations, crossing theequator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even on each other. Seabirds can be highlypelagic, 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 tohunters, guidedfishermen to fishing stocks, and ledsailors to land. Many species are currentlythreatened by human activities such asoil spills, nets,climate change and severe weather.Conservation efforts include the establishment of wildlife refuges and adjustments to fishing techniques.
There exists no single definition of which groups, families and species are seabirds, and most definitions are in some way arbitrary. Elizabeth Shreiber and Joanna Burger, two seabird scientists, said, "The one common characteristic that all seabirds share is that they feed insaltwater; but, as seems to be true with any statement in biology, some do not."[3] However, by convention, all of theSphenisciformes (penguins), all of thePhaethontiformes (tropicbirds), all of theProcellariiformes (albatrosses andpetrels), all of theSuliformes (gannets,boobies,frigatebirds, andcormorants) except thedarters, one family of thePelecaniformes (pelicans), and some of theCharadriiformes (gulls,skuas,terns,auks, andskimmers) are classified as seabirds. Thephalaropes are usually included as well, since although they arewaders ("shorebirds" in North America), two of the three species (red andred-necked) are oceanic for nine months of the year, crossing the equator to feed pelagically.[4][5]
Loons andgrebes, which nest on lakes but winter at sea, are usually categorized as water birds, not seabirds. Although there are a number ofsea ducks in the familyAnatidae that are truly marine in the winter, by convention they are usually excluded from the seabird grouping. Manyherons andwaders (or shorebirds), such ascrab-plovers, are also highly marine, living on the sea's edge (coast), but are also not treated as seabirds. Fish-eating birds of prey, such assea eagles andospreys, are also typically excluded, however tied to marine environments they may be.[6] Some birds, such asdarters andanhingas, are primarily found in freshwater habitats, but may occasionally venture into marine or coastal areas as well;[7][8] such birds are generally not considered to be seabirds.
German ornithologistGerald Mayr defined the "core waterbird" cladeAequornithes in 2010. This lineage gives rise to theProcellariiformes,Sphenisciformes,Suliformes,Pelecaniformes,Ciconiiformes (not seabirds), andGaviiformes (not seabirds).[9] Thetropicbirds (Phaethontiformes) are part of theEurypygimorphae lineage, which issister to the Aequornithes;[10] this clade also includes the non-seabirdEurypygiformes (kagu andsunbittern). TheCharadriiformes are more distantly related to the other seabirds, being more closely related to the non-seabirdGruiformes (rails andcranes) andOpisthocomiformes (hoatzin) in the cladeGruae.[11]
Seabirds, by virtue of living in ageologically depositional environment (that is, in the sea wheresediments are readily laid down), are well represented in thefossil record.[3] They are first known to occur in theCretaceous period, the earliest being theHesperornithes. These were flightless seabirds that could dive in a fashion similar to grebes and loons (using its feet to move underwater),[12] but had beaks filled with sharp teeth.[13] Other Cretaceous seabirds included the gull-likeIchthyornithes.[14] Flying Cretaceous seabirds do not exceed wingspans of two meters; piscivorouspterosaurs occupied seagoing niches above this size.[15]
WhileHesperornis is not thought to have left descendants, the earliestmodern seabirds also occurred in the Cretaceous, with a species calledTytthostonyx glauconiticus, which has features suggestive of Procellariiformes and Fregatidae.[16] As a clade, the Aequornithes either became seabirds in a single transition in the Cretaceous or some lineages such as pelicans and frigatebirds adapted to sea living independently from freshwater-dwelling ancestors.[17] In thePaleogene both pterosaurs and marine reptiles became extinct, allowing seabirds to expand ecologically. These post-extinction seas were dominated by earlyProcellariidae, giantpenguins and twoextinctfamilies, thePelagornithidae and thePlotopteridae (a group of large seabirds that looked like the penguins).[18] Modern genera began their wide radiation in theMiocene, although thegenusPuffinus (which includes today'sManx shearwater andsooty shearwater) might date back to theOligocene.[3] Within the Charadriiformes, the gulls and allies (Lari) became seabirds in the late Eocene, and then waders in the middle Miocene (Langhian).[17] The highest diversity of seabirds apparently existed during the Late Miocene and thePliocene. At the end of the latter, the oceanicfood web had undergone a period of upheaval due to extinction of considerable numbers of marine species; subsequently, the spread of marine mammals seems to have prevented seabirds from reaching their erstwhile diversity.[19][needs update]
Seabirds have made numerous adaptations to living on and feeding in the sea.Wing morphology has been shaped by theniche an individual species or family hasevolved, so that looking at a wing's shape andloading can tell a scientist about its life feeding behaviour. Longer wings and low wing loading are typical of morepelagic species, while diving species have shorter wings.[20] Species such as thewandering albatross, which forage over huge areas of sea, have a reduced capacity for powered flight and are dependent on a type ofgliding calleddynamic soaring (where the wind deflected by waves provides lift) as well as slope soaring.[21] Seabirds also almost always havewebbed feet, to aid movement on the surface as well as assisting diving in some species. TheProcellariiformes are unusual among birds in having a strongsense of smell, which is used to find widely distributed food in a vast ocean,[22] and help distinguish familiar nest odours from unfamiliar ones.[23]
Salt glands are used by seabirds to deal with thesalt they ingest by drinking and feeding (particularly oncrustaceans), and to help themosmoregulate.[25] Theexcretions from these glands (which are positioned in the head of the birds, emerging from thenasal cavity) are almost puresodium chloride.[26]
With the exception of thecormorants and some terns, and in common with most other birds, all seabirds have waterproofplumage. However, compared to land 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 ofdown feathers. The cormorants possess a layer of unique feathers that retain a smaller layer of air (compared to other diving birds) but otherwise soak up water.[24] This allows them to swim without fighting thebuoyancy that retaining air in the feathers causes, yet retain enough air to prevent the bird losing excessive heat through contact with water.[27]
The plumage of most seabirds is less colourful than that of land birds, restricted in the main to variations of black, white or grey.[20] A few species sport colourful plumes (such as the tropicbirds and 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 forcamouflage, both defensive (the colour ofUS Navybattleships is the same as that ofAntarctic prions,[20] and in both cases it reduces visibility at sea) and aggressive (the white underside possessed by many seabirds helps hide them from prey below). The usually black wing tips help prevent wear, as they contain melanins that help the feathers resist abrasion.[28]
Seabirds evolved to exploit different food resources in the world's seas and oceans, and to a great extent, theirphysiology andbehaviour have been shaped by theirdiet. 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 remarkableconvergent evolution, such as that between auks and penguins. There are four basic feeding strategies, or ecological guilds, for feeding at sea: surface feeding, pursuit diving, plunge diving, and predation ofhigher vertebrates; within these guilds, there are multiple variations on the theme.[29]
Many seabirds feed on the ocean's surface, as the action of marinecurrents often concentrates food such askrill,forage 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 whileflying (for example as practiced bygadfly petrels,frigatebirds, andstorm petrels), and surface feeding while swimming (examples of which are practiced bygulls,fulmars, many of theshearwaters and gadfly petrels). Surface feeders in flight include some of the most acrobatic of seabirds, which either snatch morsels from the water (as do frigatebirds and some terns), or "walk", pattering and hovering on the water's surface, as some of the storm petrels do.[30] 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.[31] Another seabird family that does not land while feeding is theskimmer, 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.[32]
Surface feeders that swim often have unique bills as well, adapted for their specific prey.Prions have special bills with filters calledlamellae to filter outplankton from mouthfuls of water,[33] and many albatrosses and petrels have hooked bills to snatch fast-moving prey. On the other hand, most gulls are versatile and opportunistic feeders who will eat a wide variety of prey, both at sea and on land.[34]
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. Underwaterpropulsion is provided by wings (as used by penguins, auks,diving petrels and some other species of petrel) orfeet (as used by cormorants,grebes,loons and several types of fish-eatingducks). Wing-propelled divers are generally faster than foot-propelled divers.[3] The use of wings or feet for diving has limited their utility in other situations: loons and grebes walk with extreme difficulty (if at all), penguins cannot fly, and auks have sacrificed flight efficiency in favour of diving. For example, therazorbill (an Atlantic auk) requires 64% more energy to fly than a petrel of equivalent size.[35] Manyshearwaters are intermediate between the two, having longer wings than typical wing-propelled divers but heavier wing loadings than the other surface-feedingprocellariids, leaving them capable of diving to considerable depths while still being efficient long-distance travellers. Theshort-tailed shearwater is the deepest diver of the shearwaters, having been recorded diving below 70 metres (230 ft).[36]
Some albatross species are also capable of limited diving, withlight-mantled sooty albatrosses holding the record at 12 metres (40 ft).[37] Of all the wing-propelled pursuit divers, the most efficient in the air are the albatrosses, and they are also the poorest divers. This is the dominant guild in polar and subpolar environments, but 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.[38]
Gannets,boobies,tropicbirds, some terns, andbrown pelicans all engage in plunge diving, taking fast-moving prey by diving into the water from flight. Plunge diving allows birds to use the energy from the momentum of the dive to combat natural buoyancy (caused by air trapped in plumage),[39] and thus uses less energy than the dedicated pursuit divers, allowing them to utilise more widely distributed food resources, for example, in impoverishedtropical seas. In general, this is the most specialised method of hunting employed by seabirds; other non-specialists (such as gulls and skuas) may employ it but do so with less skill and from lower heights. In brown pelicans, the skills of plunge diving take several years to fully develop—once mature, they can dive from 20 m (66 ft) above the water's surface, shifting the body before impact to avoid injury.[40]
It may be that plunge divers are restricted in their hunting grounds to clear waters that afford a view of their prey from the air.[41] While they are the dominantguild in the tropics, the link between plunge diving andwater clarity is inconclusive.[42] Some plunge divers (as well as some surface feeders) are dependent ondolphins andtuna to push shoaling fish up towards the surface.[43]
This catch-all category refers to other seabird strategies that involve the nexttrophic level up.Kleptoparasites are seabirds that make a part of their living stealing food of other seabirds. Most famously,frigatebirds andskuas engage in this behaviour, although gulls, terns and other species will steal food opportunistically.[44] Thenocturnal nesting behaviour of some seabirds has been interpreted as arising due to pressure from this aerial piracy.[45] 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.[3] A study ofgreat frigatebirds stealing frommasked boobies estimated that the frigatebirds could at most obtain 40% of the food they needed, and on average obtained only 5%.[46] Many species of gull will feed on seabird and sea mammalcarrion when the opportunity arises, as willgiant petrels. Some species of albatross also engage in scavenging: an analysis of regurgitatedsquid 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.[47] Some species will also feed on other seabirds; for example, gulls, skuas and pelicans will often take eggs, chicks and even small adult seabirds from nesting colonies, while the giant petrels can kill prey up to the size of small penguins and seal pups.[48]
Seabirds' life histories are dramatically different from those of land birds. In general, they areK-selected, live much longer (anywhere between twenty and sixty years), delay breeding for longer (for up to ten years), and invest more effort into fewer young.[3][49] Most species will only have oneclutch a year, unless they lose the first (with a few exceptions, like theCassin's auklet),[50] and many species (like thetubenoses andsulids) will only lay one egg a year.[33]
Care of young is protracted, extending for as long as six months, among the longest for birds. For example, oncecommon guillemot chicksfledge, they remain with the male parent for several months at sea.[35] The frigatebirds have the longest period of parental care of any bird except a few raptors and thesouthern ground hornbill,[51] with each chick fledging after four to six months and continued assistance after that for up to fourteen months.[52] 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.[3]
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 seasonallymonogamous. Many species, such as gulls, auks and penguins, retain the same mate for several seasons, and manypetrel species mate for life.[33] Albatrosses andprocellariids, which mate for life, 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.[53]
Ninety-five percent of seabirds are colonial,[3] and seabird colonies are among 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 tropics (such asKiritimati in thePacific) and in the polar latitudes (as inAntarctica). 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.[54]
Seabird colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed as with amurre colony. In most seabird colonies, several different species will nest on the same colony, often exhibiting someniche separation. Seabirds can nest in trees (if any are available), on the ground (with or withoutnests), on cliffs, inburrows under the ground and in rocky crevices. Competition can be strong both within species and between species, with aggressive species such assooty terns pushing less dominant species out of the most desirable nesting spaces.[55] The tropicalBonin petrel nests during the winter to avoid competition with the more aggressivewedge-tailed shearwater. When the seasons overlap, the wedge-tailed shearwaters will kill young Bonin petrels in order to use their burrows.[56]
Many seabirds show remarkable sitefidelity, returning to the same burrow, nest or site for many years, and they will defend that site from rivals with great vigour.[3] This increases breeding success, provides a place for returning mates to reunite, and reduces the costs of prospecting for a new site.[57] Young adults breeding for the first time usually return to their natal colony, and often nest close to where they hatched. This tendency, known asphilopatry, is so strong that a study ofLaysan albatrosses found that the average distance between hatching site and the site where a bird established its own territory was 22 metres (72 ft);[58] another study, this time onCory's shearwaters nesting nearCorsica, 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.[59]
Colonies are usually situated on islands, cliffs or headlands, which land mammals have difficulty accessing.[60] This is thought to provide protection to seabirds, which are often very clumsy on land. Coloniality often arises in types of birds that do not defend feeding territories (such asswifts, which have a very variable prey source); this may be a reason why it arises more frequently in seabirds.[3] 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 ofpredators, principally other birds, and many species attend their colonies nocturnally to avoid predation.[61] Birds from different colonies often forage in different areas to avoid competition.[62]
Like many birds, seabirds oftenmigrate after thebreeding season. Of these, the trip taken by theArctic tern is the farthest of any bird, crossing theequator 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 ofelegant terns, which nest offBaja California, splits after the breeding season with some birds travelling north to theCentral Coast of California and some travelling as far south as Peru and Chile to feed in theHumboldt Current.[63] Thesooty 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 64,000 kilometres (40,000 mi).[64]
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.[65] 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.[35] Other species, such as some of the storm petrels, diving petrels and cormorants, never disperse at all, staying near their breeding colonies year round.[66][67][68]
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 tens, hundreds or even thousands of miles inland. Some of these species still return to the ocean to feed; for example, thesnow petrel, the nests of which have been found 480 kilometres (300 mi) inland on the Antarctic mainland, are unlikely to find anything to eat around their breeding sites.[69] Themarbled murrelet nests inland inold growth forest, seeking hugeconifers with large branches to nest on.[70] Other species, such as theCalifornia gull, nest and feed inland on lakes, and then move to the coasts in the winter.[71] Some cormorant,pelican, gull and tern species have individuals that never visit the sea at all, spending their lives on lakes, rivers,swamps and, in the case of some of the gulls, cities andagricultural land. In these cases, it is thought that these terrestrial or freshwater birds evolved from marine ancestors.[20] Some seabirds, principally those that nest intundra, as skuas and phalaropes do, will migrate over land as well.[4][72]
The more marine species, such as petrels, auks andgannets, 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 great numbers to exhausted adults after largestorms, an event known as awreck.[73]
Seabirds have had a long association with bothfisheries andsailors, and both have drawn benefits and disadvantages from the relationship.
Fishermen have traditionally used seabirds as indicators of bothfish shoals,[43] underwaterbanks that might indicate fish stocks, and of potential landfall. In fact, the known association of seabirds with land was instrumental in allowing thePolynesians to locate tiny landmasses in the Pacific.[3] Seabirds have provided food for fishermen away from home, as well as bait. Famously, tethered cormorants have been used to catch fish directly. Indirectly, fisheries have also benefited fromguano from colonies of seabirds acting asfertilizer for the surrounding seas.[74]
Negative effects on fisheries are mostly restricted to raiding by birds onaquaculture,[75] althoughlong-lining fisheries also have to deal withbait 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 ofmarine mammals and predatory fish (liketuna).[3]
Some seabird species have benefited from fisheries, particularly from discarded fish andoffal. These discards compose 30% of the food of seabirds in theNorth Sea, for example, and compose up to 70% of the total food of some seabird populations.[76] This can have other impacts; for example, the spread of thenorthern fulmar through theUnited Kingdom is attributed in part to the availability of discards.[77] Discards generally benefit surface feeders, such as gannets and petrels, to the detriment of pursuit divers like penguins and guillemots, which can get entangled in the nets.[78]
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.[79][80][needs update] Overall, many hundreds of thousands of birds are trapped and killed each year, a source of concern for some of the rarest species (for example, only about 2,000short-tailed albatrosses are known to still exist). Seabirds are also thought to suffer when overfishing occurs.[81] Changes to the marine ecosystems caused by dredging, which alters the biodiversity of the seafloor, can also have a negative impact.[82]
Thehunting of seabirds and the collecting of seabirdeggs have contributed to the declines of many species, and theextinction of several, including thegreat auk and thespectacled cormorant. Seabirds have been hunted for food by coastal peoples throughout history—one of the earliest instances known is in southern Chile, wherearchaeological excavations in middens has shown hunting of albatrosses, cormorants and shearwaters from 5000 BP.[83] This pressure has led to some species becoming extinct in many places; in particular, at least 20 species of an original 29 no longer breed onEaster Island. In the 19th century, the hunting of seabirds forfat deposits and feathers for themillinery trade reached industrial levels.Muttonbirding (harvesting shearwater chicks) developed as important industries in both New Zealand and Tasmania, and the name of one species, theprovidence petrel, is derived from its seemingly miraculous arrival onNorfolk Island where it provided a windfall for starving European settlers.[84] In theFalkland 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 settlements grow in areas near a colony. Eggers fromSan Francisco took almost half a million eggs a year from theFarallon Islands in the mid-19th century, a period in the islands' history from which the seabird species are still recovering.[85]
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, theMāori ofStewart Island / Rakiura continue to harvest the chicks of the sooty shearwater as they have done for centuries, using traditional stewardship,kaitiakitanga, to manage the harvest, but now also work with theUniversity of Otago in studying the populations.[86] InGreenland, however, uncontrolled hunting is pushing many species into steep decline.[87]
Other human factors have led to declines and even extinctions in seabird populations and species. Of these, perhaps the most serious areintroduced species. Seabirds, breeding predominantly on small isolated islands, are vulnerable to predators because they have lost many behaviours associated with defence from predators.[60]Feral cats can take seabirds as large as albatrosses, and many introduced rodents, such as thePacific rat, take eggs hidden in burrows. Introduced goats, cattle, rabbits and otherherbivores can create problems, particularly when species need vegetation to protect or shade their young.[88] The disturbance of breeding colonies by humans is often a problem as well—visitors, even well-meaning tourists, can flush brooding adults off a colony, leaving chicks and eggs vulnerable to predators.[89][90]
The build-up oftoxins and pollutants in seabirds is also a concern. Seabirds, beingapex predators, suffered from the ravages of the insecticideDDT until it was banned; DDT was implicated, for example, in embryo development problems and the skewed sex ratio ofwestern gulls in southern California.[91]Oil spills are also a threat to seabirds: the oil is toxic, and bird feathers become saturated by the oil, causing them to lose their waterproofing.[92] Oil pollution in particular threatens species with restricted ranges or already depressed populations.[93][94]
Climate change mainly affect seabirds via changes to theirhabitat: various processes in the ocean lead to decreased availability of food and colonies are more often flooded as a consequence ofsea level rise and extreme rainfall events. Heat stress from extreme temperatures is an additional threat.[95] Some seabirds have used changing wind patterns to forage further and more efficiently.[96]
In 2023,plasticosis, a new disease caused solely by plastics, was discovered in seabirds.The birds identified as having the disease have scarred digestive tracts from ingestingplastic waste.[97] "When birds ingest small pieces of plastic, they found, it inflames the digestive tract. Over time, the persistent inflammation causes tissues to become scarred and disfigured, affecting digestion, growth and survival."[98]
The threats faced by seabirds have not gone unnoticed by scientists or theconservation movement. As early as 1903, U.S. PresidentTheodore Roosevelt was convinced of the need to declarePelican Island in Florida aNational Wildlife Refuge to protect the bird colonies (including the nestingbrown pelicans),[99] and in 1909 he protected the Farallon Islands. Today many important seabird colonies are given some measure of protection, fromHeron Island in Australia toTriangle Island in British Columbia.[100][101]
Island restoration techniques, pioneered by New Zealand, enable the removal of exotic invaders from increasingly large islands. Feral cats have been removed fromAscension Island,Arctic foxes from many islands in theAleutian Islands,[102] and rats fromCampbell Island. 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.[103]
Seabird mortality caused bylong-line fisheries can be greatly 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,[104] and their deployment is increasingly required by many national fishing fleets.
One of the Millennium Projects in the UK was theScottish Seabird Centre, near the important bird sanctuaries onBass Rock,Fidra and the surrounding islands. The area is home to huge colonies of gannets,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. Seabird tourism can provide income for coastal communities as well as raise the profile of seabird conservation, although it needs to be managed to ensure it does not harm the colonies and nesting birds.[105] For example, thenorthern royal albatross colony atTaiaroa Head in New Zealand attracts 40,000 visitors a year.[33]
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 ofnon-governmental organizations (includingBirdLife International, theAmerican Bird Conservancy and theRoyal Society for the Protection of Birds).[106][107][108] This led to theAgreement on the Conservation of Albatrosses and Petrels, a legally binding treaty designed to protect these threatened species, which has been ratified by thirteen countries as of 2021 (Argentina, Australia, Brazil, Chile, Ecuador, France, New Zealand, Norway, Peru, South Africa, Spain, Uruguay, United Kingdom).[109]
Many seabirds are little studied and poorly known because they live far out at sea and breed in isolated colonies. Some seabirds, particularly the albatrosses and gulls, are more well known to humans. The albatross has been described as "the most legendary of birds",[110] and have a variety of myths and legends associated with them. While it is widely considered unlucky to harm them, the notion that sailors believed that is a myth[111] that derives fromSamuel 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. Sailors did, however, consider it unlucky to touch a storm petrel, especially one that landed on the ship.[112]
Gulls are one of the most commonly seen seabirds because they frequent human-made habitats (such as cities anddumps) and often show a fearless nature. Gulls have been used as metaphors, as inJonathan Livingston Seagull byRichard Bach, or to denote a closeness to the sea; inThe Lord of the Rings, they appear in the insignia ofGondor and thereforeNúmenor (used in the design of the films), and they callLegolas to (and across) the sea. Pelicans have long been associated with mercy andaltruism because of an earlyChristian myth that they split open their breast to feed their starving chicks.[40]
The following are the groups of birds normally classed as seabirds.[citation needed] For each order, the species counts given are for only the seabird portions (i.e. the listed groups), not the total number of species.
Sphenisciformes (18 species; Antarctic and southern waters)
Procellariiformes (149 species; pan-oceanic and pelagic)
Pelecaniformes (8 species; worldwide)
Suliformes (57 species; worldwide)
Phaethontiformes (3 species; worldwide tropical seas)
Charadriiformes (138 species; worldwide)
For an alternative taxonomy of these groups, see alsoSibley-Ahlquist taxonomy.
Before visiting or leaving their remote island colonies, seabirds in often engage in a behaviour termed 'rafting', where birds sit, often in groups, on the water close to the colony.
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