(Redirected from Seabirds)
The
Sooty Tern is highly aerial and marine and will spend years flying at sea without returning to land.
'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
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
sailors 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
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 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 categorised 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.
Evolution and fossil record
Seabirds, by virtue of living in a
geologically depositional environment (that is, in the sea where
sediments 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)
[1] but had a beak filled with sharp teeth.
[2]
The Cretaceous seabird ''Hesperornis''
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 seems allied to the
Procellariiformes and/or
Pelecaniformes. In the
Paleogene the seas were dominated by early
Procellariidae, giant
penguins and two
extinct families, the
Pelagornithidae and the
Plotopteridae (a group of large seabirds that looked like the penguins).
[3] Modern genera began their wide radiation in the
Miocene, although the
genus ''
Puffinus'' (which includes today's
Manx Shearwater and
Sooty Shearwater) might date back to the
Oligocene.
[Schreiber, Elizabeth A. & Burger, Joanne.(2001.) ''Biology of Marine Birds'', Boca Raton:CRC Press, ISBN 0-8493-9882-7] The highest diversity of seabirds apparently existed during the Late Miocene and the
Pliocene. 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;
[4] subsequently, the spread of marine mammals seems to have prevented seabirds from reaching their erstwhile diversity.
[5]
Characteristics
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.
[Gaston, Anthony J. (2004). ''Seabirds: A Natural History'' New Haven:Yale University Press, ISBN 0-300-10406-5] 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.
[6] Seabirds also almost always have webbed feet, to aid movement on the surface as well as assisting diving in some species. The
Procellariiformes are unusual amongst birds in having a strong
sense of smell, which is used to find widely distributed food in a vast ocean,
[7] and possibly to locate their colonies.
Salt glands are used by seabirds to deal with the
salt they ingest by drinking and feeding (particularly on
crustaceans), and to help them
osmoregulate.
[Harrison, C. S. (1990) ''Seabirds of Hawaii, Natural History and Conservation'' Ithica:Cornell University Press, ISBN 0-8014-2449-6] The
excretions from these glands (which are positioned in the head of the birds, emerging from the
nasal cavity) are almost pure
sodium chloride.
Cormorants, like this Double-crested Cormorant, have plumage that is partly wettable, allowing them to dive without fighting buoyancy.
With the exception of the
cormorants and some terns, and in common with most other birds, all seabirds have waterproof
plumage. 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 of
down 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.
[8] This allows them to swim without fighting the
buoyancy 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 battleships is the same as that of
Antarctic Prions,
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
auks and
penguins. 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
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.
[9] 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.
[10] 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.
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 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
The Chinstrap Penguin is a highly streamlined pursuit diver.
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.
Propulsion underwater can be provided by wings (as used by penguins, auks,
diving petrels, and some other species of petrel) or feet (as used by
cormorants,
grebes,
loons and several types of fish-eating
ducks). Wing-propelled divers are generally faster than foot-propelled divers.
[Schreiber, Elizabeth A. & Burger, Joanne.(2001.) ''Biology of Marine Birds'', Boca Raton:CRC Press, ISBN 0-8493-9882-7] In both cases, 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 underwater diving. For example, the
razorbill (an
Atlantic auk) requires 64% more energy to fly than a petrel of equivalent size.
[Gaston, Anthony J. & Jones, Ian L. (1998). ''The Auks'' Oxford:Oxford University Press, ISBN 0-19-854032-9] Many
shearwaters are intermediate between the two, having longer wings than typical wing-propelled divers but heavier wing loadings than the other surface-feeding
procellariids, leaving them capable of diving to considerable depths while still being efficient long-distance travellers. The most impressive diving exhibited by shearwaters is found in the
Short-tailed Shearwater, which has been recorded diving below 70 m.
[11] Some albatross species are also capable of some limited diving, with
Light-mantled Sooty Albatrosses holding the record at 12 m.
[12] 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
Gannets,
boobies,
tropicbirds, some
terns and
Brown 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),
[13] and thus uses less energy than the dedicated pursuit divers, allowing them utilise more widely distributed food resources, for example, in impoverished
tropical 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 (70 ft) above the water's surface, shifting the body before impact to avoid injury.
[Elliot, A. (1992) "Family Pelecanidae (Pelicans)" in ''Handbook of Birds of the World'' Vol 1. Barcelona:Lynx Editions, ISBN 84-87334-10-5] It has been suggested that plunge divers are restricted in their hunting grounds to clear waters that afford a view of their prey from the air,
[14] and while they are the dominant guild in the tropics, the link between plunge diving and water clarity is inconclusive.
[15] Some plunge divers (as well as some surface feeders) are dependent on
dolphins 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. [5]]
Kleptoparasitism, scavenging and predation
This catch-all category refers to other seabird strategies that involve the next
trophic level up.
Kleptoparasites are seabirds that make a part of their living stealing food of other seabirds. Most famously,
frigatebirds and
skuas engage in this behaviour, although gulls, terns and other species will steal food opportunistically.
[16] The
nocturnal nesting behaviour of some seabirds has been interpreted as arising due to pressure from this aerial piracy.
[17] 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 Frigatebirds stealing from
Masked Boobies estimated that the frigatebirds could at most obtain 40% of the food they needed, and on average obtained only 5%.
[18] Many species of gull will feed on seabird and sea mammal
carrion when the opportunity arises, as will
giant petrels. Some species of albatross also engage in scavenging: an analysis of 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 albatrosses.
[19] 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.
[20]
Life history
Seabirds' life histories are dramatically different from those of land birds. In general, they are
K-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.
Most species will only have one
clutch a year, unless they lose the first (with a few exceptions, like the
Cassin's Auklet),
[22] and many species (like the
tubenoses and
sulids), only one egg a year.
Northern Gannet 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
frigatebirds 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.
[23] 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
procellariids 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.
[24]
Breeding and colonies
:''See also
Seabird colony
Common Murres 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
tropics (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
trees (if any are available), on the ground (with or without
nests), on
cliffs, in
burrows under the ground and in rocky crevices. Competition can be strong both within species and between species, with aggressive species such as
Sooty Terns pushing less dominant species out of the most desirable nesting spaces.
[25] 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.
[26]
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 a place for returning mates to reunite, and reduces the costs of prospecting for a new site.
[27] Young adults breeding for the first time usually return to their natal colony, and often nest close to where they hatched. This tendency, known as
philopatry, is so strong that a study of
Laysan Albatrosses found that the average distance between hatching site and the site where a bird established its own territory was 22 m;
[28] another study, this time on
Cory's Shearwaters 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.
[29]
Colonies are usually situated on islands, cliffs or headlands which land
mammals have difficulty accessing.
[Moors, P.J.; Atkinson, I.A.E. (1984). ''Predation on seabirds by introduced animals, and factors affecting its severity.''. In ''Status and Conservation of the World's Seabirds''. Cambridge: ICBP. ISBN 0-946888-03-5.] This is thought to provide protection to seabirds, which are often very clumsy on land. Coloniality often arises in types of bird which do not defend feeding territories (such as
swifts, 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
predators, principally other birds, and many species attend their colonies
nocturnally to avoid predation.
[30]
Migration
Arctic Terns breed in the arctic and subarctic and winter in Antarctica.
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.
[31] 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).
[32]
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.
[33] 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-petrels,
diving petrels and
cormorants, 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
Snow Petrel, the nests of which have been found 300 miles inland on the Antarctic mainland, are unlikely to find anything to eat around their breeding sites.
[34] The
Marbled Murrelet nests inland in
old growth forest, seeking huge
conifers with large branches to nest on.
[35] Other species, such as the
California Gull, nest and feed inland on
lakes, and then move to the coasts in the winter.
[36] 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 and
agricultural land. In these cases it is thought that these terrestrial or freshwater birds evolved from marine ancestors.
[Gaston, Anthony J. (2004). ''Seabirds: A Natural History'' New Haven:Yale University Press, ISBN 0-300-10406-5] Some seabirds, principally those that nest in
tundra-like skuas and phalaropes, will migrate over land as well.
The more marine species, such as
petrels,
auks, and
gannets, 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 large
storms, an event known as a ''wreck'',
[37] where they provide prized sightings for
birders.
Relationship with humans
Seabirds and fisheries
Seabirds have had a long association with both
fisheries and
sailors, and both have drawn benefits and disadvantages from the relationship.
Fishermen have traditionally used seabirds as indicators of both fish
shoals,
[Au, D.W.K. & Pitman, R.L. (1986) Seabird interactions with Dolphins and Tuna in the Eastern Tropical Pacific. ''Condor'', '88': 304–317. [11]] underwater
banks that might indicate fish stocks, and of potential landfall. In fact, the known association of seabirds with land was instrumental in allowing the
Polynesians to locate tiny landmasses in the Pacific.
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 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,
[38] although
long-lining 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 mammals and predatory fish (like
tuna).
Seabirds (mostly Northern Fulmars) flocking at a long-lining vessel
Some seabird species have benefited from fisheries, particularly from discarded fish and
offal. These discards compose 30% of the food of seabirds in the
North Sea, for example, and compose up to 70% of the total food of some seabird populations.
[39] This can have other impacts; for example, the spread of the
Northern Fulmar through the
British Isles is attributed in part to the availability of discards.
[40] 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.
[41][42] 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 1,000
Short-tailed Albatrosses are known to still exist). Seabirds are also thought to suffer when overfishing occurs.
Exploitation
The
hunting of seabirds and the collecting of seabird
eggs have contributed to the declines of many species, and the
extinction of several, including the
Great Auk and the
Spectacled Cormorant. Seabirds have been hunted for food by coastal peoples throughout history—one of the earliest instances known is in southern
Chile, where
archaeological excavations in middens has shown hunting of albatrosses, cormorants and shearwaters from 5000 BP.
[43] 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 on
Easter Island. In the 19th century, the hunting of seabirds for
fat deposits and feathers for the
millinery trade reached
industrial levels.
Muttonbirding (harvesting shearwater chicks) developed as important industries in both New Zealand and Tasmania, and the name of one species, the
Providence Petrel, is derived from its seemingly miraculous arrival on
Norfolk Island where it provided a windfall for starving European settlers.
[Anderson, A. (1996) "Origins of Procellariidae Hunting in the Southwest Pacific" ''International Journal of Osteoarcheology'' '6': 403–410] 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 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.
[44]
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.
[45]
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
introduced species. Seabirds, breeding predominantly on small isolated islands, have lost many predator defence behaviours.
s are capable of taking seabirds as large as albatrosses, and many introduced rodents, such as the
Pacific Rat, can take eggs hidden in burrows. Introduced
goats,
cattle,
rabbits and other
herbivores can lead to problems, particularly when species need vegetation to protect or shade their young.
[Carlile, N., Proiddel, D., Zino, F., Natividad, C. & Wingate, D.B. (2003) "A review of four successful recovery programmes for threatened sub-tropical petrels" ''Marine Ornithology'' '31': 185–192] 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.
This Crested Auklet was oiled in Alaska during the M/V
Selendang Ayu spill of 2004.
The build-up of
toxins and
pollutants in seabirds is also a concern. Seabirds, being apex predators, suffered from the ravages of
DDT until it was banned; among other effects, DDT was implicated in embryo development problems and the skewed sex ratio of
Western Gulls in southern California.
[46] Oil spills 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.
[47] 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
conservation movement. As early as 1903, U.S. President
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 Pelicans),
[48] and 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.
Island restoration techniques, pioneered by
New Zealand, enable the removal of exotic invaders from increasingly large islands. Feral cats have been removed from
Ascension Island,
Arctic Foxes from many islands in the
Aleutian Islands,
[49] and rats from
Campbell 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.
[50]
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,
[51] and their deployment is increasingly required by many national fishing fleets. The international ban on the use of
drift nets 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,
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. 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 organizations (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).
[52]
Role in culture
Depiction of a pelican with chicks on a stained glass window, Saint Mark's Church,
Gillingham,
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
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[Cocker, M., & Mabey, R., (2005) ''Birds Britannica'' London:Chatto & Windus, ISBN 0-7011-6907-9] 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.
''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
metaphorically, 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;
pelicans 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)
★ Spheniscidae
penguins
'
Procellariiformes' (Tubenoses: pan-oceanic and pelagic; 93 species)
★ Diomedeidae
albatrosses
★ Procellariidae
fulmars,
prions,
shearwaters,
gadfly and other
petrels
★ Pelacanoididae
diving petrels
★ Hydrobatidae
storm-petrels
'
Pelecaniformes' (Worldwide; 57 species)
★ Pelecanidae
pelicans
★ Sulidae
gannets and
boobies
★ Phalacrocoracidae
cormorants
★ Fregatidae
frigatebirds
★ Phaethontidae
tropicbirds
Charadriiformes (Worldwide; 305 species, but only the families listed are classed as seabirds.)
★ Stercorariidae
skuas
★ Laridae
gulls
★ Sternidae
terns
★ Rhynchopidae
skimmers
★ Alcidae
auks
For an alternative taxonomy of these groups, see also
Sibley-Ahlquist taxonomy.
See also
list of birds.
References
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52. Australian Antarctic Division Agreement on the Conservation of Albatrosses and Petrels Site Retrieved September 2 2006
External links
★
Project Titi; a collaboration between the Māori of Stewart Island and the University of Otago to manage Sooty Shearwater harvests
★
BirdLife International; Save the Albatross Campaign
★
Marine Ornithology, the Journal of Seabird Science and Conservation
★
www.seabird.org, official site of the Scottish Seabird Centre
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