Albatross
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Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Procellariiformes
Family: Diomedeidae
Genera: Diomedea, Thalassarche, Phoebastria, Phoebetria
[Photo] Short-tailed Albatross or Steller's Albatross (Phoebastria albatrus) showing tubenose structure. Date Issued: January 28 2002. Creator: Steve Moore. Source: U.S. Fish and Wildlife Service (http://images.fws.gov). License: public domain.
Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes (the tubenoses). They range widely in the Southern Ocean and the North Pacific. They are absent from the North Atlantic, although fossil remains show they once occurred there too and occasional vagrants turn up. Albatrosses are amongst the largest of flying birds, and the great albatrosses (genus Diomedea) have the largest wingspans of any extant birds. The albatrosses are usually regarded as falling into four genera, but there is disagreement over the number of species.
Albatrosses are highly efficient in the air, using dynamic soaring and slope soaring to cover great distances with little exertion. They feed on squid, fish and krill by either scavenging, surface seizing or diving. Albatrosses are colonial, nesting for the most part on remote oceanic islands, often with several species nesting together. Pair bonds between males and females form over several years, with the use of ritualised dances, and will last for the life of the pair. A breeding season can take over a year from laying to fledging, with a single egg laid in each breeding attempt.
Of the 21 species of albatrosses recognised by the IUCN, 19 are threatened with extinction. Numbers of albatrosses have declined in the past due to harvesting for feathers, but today the albatrosses are threatened by introduced species such as rats and feral cats that attack eggs, chicks and nesting adults; by pollution; by a serious decline in fish stocks in many regions largely due to overfishing; and by long-line fishing. Long-line fisheries pose the greatest threat, as feeding birds are attracted to the bait and become hooked on the lines and drown. Governments, conservation organisations and fishermen are all working towards reducing this by-catch.
Species
Current thinking divides the albatrosses into four genera. The number of species is a matter of some debate. The IUCN and BirdLife International among others recognise the interim taxonomy of 21 extant species, other authorities retain the more traditional 14 species, and one recent paper proposed a reduction to 13:
Great albatrosses (Diomedea)
Wandering Albatross Diomedea exulans
Antipodean Albatross Diomedea (exulans) antipodensis
Amsterdam Albatross Diomedea (exulans) amsterdamensis
Tristan Albatross Diomedea (exulans) dabbenena
Northern Royal Albatross Diomedea (epomorpha) sanfordi
Southern Royal Albatross Diomedea epomophora
North Pacific albatrosses (Phoebastria)
Waved Albatross Phoebastria irrorata
Short-tailed Albatross Phoebastria albatrus
Black-footed Albatross Phoebastria nigripes
Laysan Albatross Phoebastria immutabilis
Mollymawks (Thalassarche)
Black-browed Albatross Thalassarche melanophris
Campbell Albatross Thalassarche (melanophris) impavida
Shy Albatross Thalassarche cauta
Chatham Albatross Thalassarche (cauta) eremita
Salvin's Albatross Thalassarche (cauta) salvini
Grey-headed Albatross Thalassarche chrysostoma
Atlantic Yellow-nosed Albatross Thalassarche chlororhynchos
Indian Yellow-nosed Albatross Thalassarche (chlororhynchos) carteri
Buller's Albatross Thalassarche bulleri
Sooty albatrosses (Phoebetria)
Dark-mantled Sooty Albatross Phoebetria fusca
Light-mantled Sooty Albatross Phoebetria palpebrata.
Taxonomy and evolution
The albatrosses comprise between 13 and 24 species (the number of species is still a matter of some debate, 21 being the most commonly accepted number) in 4 genera. The four genera are the great albatrosses (Diomedea), the mollymawks (Thalassarche), the North Pacific albatrosses (Phoebastria), and the sooty albatrosses or sooties (Phoebetria). Of the four genera, the North Pacific albatrosses are considered to be a sister taxon to the great albatrosses, while the sooty albatrosses are considered closer to the mollymawks.
The taxonomy of the albatross group has been a source of a great deal of debate. The Sibley-Ahlquist taxonomy places seabirds, birds of prey and many others in a greatly enlarged order Ciconiiformes, whereas the ornithological organisations in North America, Europe, South Africa, Australia and New Zealand retain the more traditional order Procellariiformes. The albatrosses can be separated from the other Procellariiformes both genetically and through morphological characteristics, size, their legs and the arrangement of their nasal tubes (see Morphology and flight).
Within the family the assignment of genera has been debated for over a hundred years. Originally placed into a single genus, Diomedea, they were rearranged by Reichenbach into four different genera in 1852, then lumped back together and split apart again several times, acquiring 12 different genus names in total (though never more than eight at one time) by 1965 (Diomedea, Phoebastria, Thalassarche, Phoebetria, Thalassageron, Diomedella, Nealbatrus, Rhothonia, Julietata, Galapagornis, Laysanornis, and Penthirenia).
By 1965, in an attempt to bring some order back to the classification of albatrosses, they were lumped into two genera, Phoebetria (the sooty albatrosses which most closely seemed to resemble the procellarids and were at the time considered "primitive" ) and Diomedea (the rest). Though there was a case for the simplification of the family (particularly the nomenclature), the classification was based on the morphological analysis of Elliott Coues in 1866, and paid little attention to more recent studies and even ignored some of Coues's suggestions.
More recent research by Gary Nunn of the American Museum of Natural History (1996) and other researchers around the world studied the mitochondrial DNA of all 14 accepted species, finding that there were four, not two, monophyletic groups within the albatrosses. They proposed the resurrection of two of the old genus names, Phoebastria for the North Pacific albatrosses and Thalassarche for the mollymawks, with the great albatrosses retaining Diomedea and the sooty albatrosses staying in Phoebetria. Both the British Ornithologists' Union and the South African authorities split the albatrosses into four genera as Nunn suggested, and the change has been accepted by the majority of researchers.
While there is some agreement on the number of genera, there is less agreement on the number of species. Historically, up to 80 different taxa have been described by different researchers; most of these were incorrectly identified juvenile birds.
Based on the work on albatross genera, Robertson and Nunn went on in 1998 to propose a revised taxonomy with 24 different species, compared to the 14 then accepted. This interim taxonomy elevated many established subspecies to full species, but was criticised for not using, in every case, peer reviewed information to justify the splits. Since then further studies have in some instances supported or disproved the splits; a 2004 paper analysing the mitochondrial DNA and microsatellites agreed with the conclusion that the Antipodean Albatross and the Tristan Albatross were distinct from the Wandering Albatross, per Robertson and Nunn, but found that the suggested Gibson's Albatross, Diomedea gibsoni, was not distinct from the Antipodean Albatross. For the most part, an interim taxonomy of 21 species is accepted by the IUCN and many other researchers, though by no means all ??? in 2004 Penhallurick and Wink called for the number of species to be reduced to 13 (including the lumping of the Amsterdam Albatross with the Wandering Albatross), although this paper was itself controversial. On all sides, there is the widespread agreement on the need for further research to clarify the issue.
Sibley and Ahlquist's molecular study of the evolution of the bird families has put the radiation of the Procellariiformes in the Oligocene period (35???30 million years ago), though this group probably originated earlier, with a fossil sometimes attributed to the order, a seabird known as Tytthostonyx, being found in late Cretaceous rocks (70 mya). The molecular evidence suggests that the storm-petrels were the first to diverge from the ancestral stock, and the albatrosses next, with the procellarids and diving petrels separating later. The earliest fossil albatrosses were found in Eocene to Oligocene rocks, although some of these are only tentatively assigned to the faimly and none appear to be particularly close to the living forms. They are Murunkus (Middle Eocene of Uzbekistan), Manu (early Oligocene of New Zealand), and an undescribed form from the Late Oligocene of South Carolina. Similar to the last was Plotornis, formerly often considered a petrel but now accepted as an albatross. It is from the Middle Miocene of France, a time when the split between the four modern genera was already underway as evidenced by Phoebastria californica and Diomedea milleri, both being mid-Miocene species from Sharktooth Hill, California. These show that the split between the great albatrosses and the North Pacific albatrosses occurred by 15 mya. Similar fossil finds in the southern hemisphere put the split between the sooties and mollymawks at 10 mya. The fossil record of the albatrosses in the northern hemisphere is more complete than that of the southern, and many fossil forms of albatross have been found in the North Atlantic, which today has no albatrosses. The remains of a colony of Short-tailed Albatrosses have been uncovered on the island of Bermuda, and the majority of fossil albatrosses from the North Atlantic have been of the genus Phoebastria (the North Pacific albatrosses); one, Phoebastria anglica, has been found in deposits in both North Carolina and England. See the genus accounts for more data on fossil species.
Morphology and flight
The albatrosses are a group of large to very large birds; they are the largest of the procellariiformes. The bill is large, strong and sharp-edged, the upper mandible terminating in a large hook. This bill is composed of several horny plates, and along the sides are the two "tubes", long nostrils that give the order its former name. The tubes of all albatrosses are along the sides of the bill, unlike the rest of the Procellariiformes where the tubes run along the top of the bill. These tubes allow the albatrosses to have an acute sense of smell, an unusual ability for birds. Like other Procellariiformes they use this olfactory ability while foraging in order to locate potential food sources. The feet have no hind toe and the three anterior toes are completely webbed. The legs are strong for Procellariiformes, in fact, almost uniquely amongst the order in that they and the giant petrels are able to walk well on land.
The adult plumage of most of the albatrosses is usually some variation of dark upper-wing and back, white undersides, often compared to that of a gull. Of these, the species range from the Southern Royal Albatross which is almost completely white except for the ends and trailing edges of the wings in fully mature males, to the Amsterdam Albatross which has an almost juvenile-like breeding plumage with a great deal of brown, particularly a strong brown band around the chest. Several species of mollymawks and North Pacific albatrosses have face markings like eye patches or have grey or yellow on the head and nape. Three albatross species, the Black-footed Albatross and the two sooty albatrosses, vary completely from the usual patterns and are almost entirely dark brown (or dark grey in places in the case of the Light-mantled Sooty Albatross). Albatrosses take several years to get their full adult breeding plumage.
The wingspans of the largest great albatrosses (genus Diomedea) are the largest of any bird, exceeding 340 cm (over 11 feet), although the other species' wingspans are considerably smaller. The wings are stiff and cambered, with thickened streamlined leading edges. Albatrosses travel huge distances with two techniques used by many long-winged seabirds, dynamic soaring and slope soaring. Dynamic soaring enables them to minimise the effort needed by gliding across wave fronts gaining energy from the vertical wind gradient. Slope soaring is more straightforward: the albatross turns to the wind, gaining height, from where it can then glide back down to the sea. Albatross have high glide ratios, around 22:1 to 23:1, meaning that for every metre they drop, they can travel forward 22 metres. They are aided in soaring by a shoulder-lock, a sheet of tendon that locks the wing when fully extended, allowing the wing to be kept outstretched without any muscle expenditure, a morphological adaptation they share with the giant petrels.
Albatrosses combine these soaring techniques with the use of predictable weather systems; albatrosses in the southern hemisphere flying north from their colonies will take a clockwise route, and those flying south will fly counterclockwise. Albatrosses are so well adapted to this lifestyle that their heart rates while flying are close to their basal heart rate when resting. This efficiency is such that the most energetically demanding aspect of a foraging trip is not the distance covered, but the landings, take-offs and hunting they undertake having found a food source. This efficient long-distance travelling underlies the albatross's success as a long-distance forager, covering great distances and expending little energy looking for patchily distributed food sources. Their adaptation to gliding flight makes them dependent on wind and waves, however, as their long wings are ill-suited to powered flight and most species lack the muscles and energy to undertake sustained flapping flight. Albatrosses in calm seas are forced to rest on the ocean's surface until the wind picks up again. They also sleep while resting on the surface (and not while on the wing as is sometimes thought). The North Pacific albatrosses can use a flight style known as flap-gliding, where the bird progresses by bursts of flapping followed by gliding. When taking off, albatrosses need to take a run up to allow enough air to move under the wing to provide lift.
Distribution and range at sea
Most albatrosses range in the southern hemisphere from Antarctica to Australia, South Africa and South America. The exceptions to this are the four North Pacific albatrosses, of which three occur exclusively in the North Pacific, from Hawaii to Japan, California and Alaska; and one, the Waved Albatross, breeds in the Galapagos Islands and feeds off the coast of South America. The need for wind in order to glide is the reason albatrosses are for the most part confined to higher latitudes; being unsuited to sustained flapping flight makes crossing the doldrums extremely difficult. The exception, the Waved Albatross, is able to live in the equatorial waters around the Galapagos Islands because of the cool waters of the Humboldt Current and the resulting winds.
It is not known for certain why the albatrosses became extinct in the North Atlantic, although rising sea levels due to an interglacial warming period are thought to have submerged the site of a Short-tailed Albatross colony that has been excavated in Bermuda. Some southern species have occasionally turned up as vagrants in the North Atlantic and can become exiled, remaining there for decades. One of these exiles, a Black-browed Albatross, returned to gannet colonies in Scotland for many years in a lonely attempt to breed.
The use of satellite tracking is teaching scientists a great deal about the way albatrosses forage across the ocean in order to find food. They undertake no annual migration, but disperse widely after breeding, in the case of southern hemisphere species, often undertaking circumpolar trips. There is also evidence that there is separation of the ranges of different species at sea. A comparison of the foraging niches of two related species that breed on Campbell Island, the Campbell Albatross and the Grey-headed Albatross, showed the Campbell Albatross primarily fed over the Campbell Plateau whereas the Grey-Headed Albatross fed in more pelagic, oceanic waters. Wandering Albatrosses also react strongly to bathymetry, feeding only in waters deeper than 1000 m (3281 feet); so rigidly did the satellite plots match this contour that one scientist remarked, "It almost appears as if the birds notice and obey a 'No Entry' sign where the water shallows to less than 1000 m". There is also evidence of different ranges for the two sexes of the same species; a study of Tristan Albatrosses breeding on Gough Island showed that males foraged to the west of Gough and females to the east.
Diet
The albatross diet is dominated by cephalopods, fish and crustaceans, although they will also scavenge carrion and feed on other zooplankton. It should be noted that for most species, a comprehensive understanding of diet is only known for the breeding season, when the albatrosses regularly return to land and study is possible. The importance of each of these food sources varies from species to species, and even from population to population; some concentrate on squid alone, others take more krill or fish. Of the two albatross species found in Hawaii, one, the Black-footed Albatross, takes mostly fish while the Laysan feeds on squid.
The use of dataloggers at sea that record ingestion of water against time (providing a likely time of feeding) suggest that albatross predominantly feed during the day. Analysis of the squid beaks regurgitated by albatrosses has shown that many of the squid eaten are too large to have been caught alive, and include mid-water species likely to be beyond the reach of albatross, suggesting that, for some species (like the Wandering Albatross), scavenged squid may be an important part of the diet. The source of these dead squid is a matter of debate; some certainly comes from squid fisheries, but in nature it primarily comes from the die-off that occurs after squid spawning and the vomit of squid-eating whales (sperm whales, pilot whales and Southern Bottlenose Whales). The diet of other species, like the Black-browed Albatross or the Grey-headed Albatross, is rich with smaller species of squid that tend to sink after death, and scavenging is not assumed to play a large role in their diet.
Until recently it was thought that albatross were predominantly surface feeders, swimming at the surface and snapping up squid and fish pushed to the surface by currents, predators or death. The deployment of capillary depth recorders, which record the maximum dive depth undertaken by a bird (between attaching it to a bird and recovering it when it returns to land), has shown that while some species, like the Wandering Albatross, do not dive deeper than a metre, some species, like the Light-mantled Sooty Albatross, have a mean diving depth of almost 5 m and can dive as deep as 12.5 m. In addition to surface feeding and diving, they have now also been observed plunge diving from the air to snatch prey.
Breeding
Albatrosses are colonial, usually nesting on isolated islands; where colonies are on larger landmasses, they are found on exposed headlands with good approaches from the sea in several directions, like the colony on the Otago Peninsula in Dunedin, New Zealand. Colonies vary from the very dense aggregations favoured by the mollymawks (Black-browed Albatross colonies on the Falkland Islands have densities of 70 nests per 100 m²) to the much looser groups and widely spaced individual nests favoured by the sooty and great albatrosses. All albatross colonies are on islands that historically were free of land mammals. Albatrosses are highly philopatric, meaning they will usually return to their natal colony to breed. This tendency to return is so strong that a study of Laysan Albatross showed that the average distance between hatching site and the site where a bird established its own territory was 22 metres.
Like most seabirds, albatrosses are K-selected with regard to their life history, meaning they live much longer than other birds, they delay breeding for longer, and invest more effort into fewer young. Albatrosses are very long lived; most species survive upwards of 50 years, the oldest recorded being a Northern Royal Albatross that was ringed as an adult and survived for another 51 years, giving it an estimated age of 61. Given that most albatross ringing projects are considerably younger than that, it is thought likely that other species will prove to live that long and even longer.
Albatrosses reach sexual maturity slowly, after about five years, but even once they have reached maturity, they will not begin to breed for another couple of years (even up to 10 years for some species). Young non-breeders will attend a colony prior to beginning to breed, spending many years practicing the elaborate breeding rituals and "dances" that the family is famous for. Birds arriving back at the colony for the first time already have the stereotyped behaviours that compose albatross language, but can neither "read" that behaviour as exhibited by other birds nor respond appropriately. After a period of trial and error learning, the young birds learn the syntax and perfect the dances. This language is mastered more rapidly if the younger birds are around older birds.
The repertoire of behaviour involves synchronised performances of various actions such as preening, pointing, calling, bill clacking, staring, and combinations of such behaviours (like the sky-call). When a bird first returns to the colony it will dance with many partners, but after a number of years the number of birds an individual will interact with drops, until one partner is chosen and a pair is formed. They then continue to perfect an individual language that will eventually be unique to that one pair. Having established a pair bond that will last for life, however, most of that dance will never be used ever again.
Albatrosses are thought to undertake these elaborate and painstaking rituals to ensure that the correct partner has been chosen and to perfect recognition of their partner, as egg laying and chick rearing is a huge investment. Even species that can complete an egg-laying cycle in under a year seldom lay eggs in consecutive years. The great albatrosses (like the Wandering Albatross) take over a year to raise a chick from laying to fledging. Albatrosses lay a single egg in a breeding season; if the egg is lost to predators or accidentally broken, then no further breeding attempts are made that year. The "divorce" of a pair is a rare occurrence, usually only happening after several years of breeding failure.
All the southern albatrosses create large nests for their egg, whereas the three species in the north Pacific make more rudimentary nests. The Waved Albatross, on the other hand, makes no nest and will even move its egg around the pair's territory, as much as 50 m, sometimes causing it to lose the egg. In all albatross species, both parents incubate the egg in stints that last between one day and three weeks. Incubation lasts around 70 to 80 days (longer for the larger albatrosses), the longest incubation period of any bird. It can be an energetically demanding process, with the adult losing as much as 83 g of body weight a day.
After hatching, the chick is brooded and guarded for three weeks until it is large enough to defend and thermoregulate itself. During this period the parents feed the chick small meals when they relieve each other from duty. After the brooding period is over, the chick is fed in regular intervals by both parents. The parents adopt alternative patterns of short and long foraging trips, providing meals that weigh around 12% of their body weight (around 600 g). The meals are composed of both fresh squid, fish and krill, as well as stomach oil, an energy-rich food that is lighter to carry than undigested prey items. This oil is created in a stomach organ known as a proventriculus from digested prey items by most tubenoses, and gives them their distinctive musty smell.
Albatross chicks take a long time to fledge. In the case of the great albatrosses, it can take up to 280 days; even for the smaller albatrosses, it takes anywhere between 140 and 170 days. Like many seabirds, albatross chicks will gain enough weight to be heavier than their parents, and prior to fledging they use these reserves to build up body condition (particularly growing all their flight feathers), usually fledging at the same weight as their parents. Albatross chicks fledge on their own and receive no further help from their parents, who return to the nest after fledging, unaware their chick has left. Studies of juveniles dispersing at sea have suggested an innate migration behaviour, a genetically coded navigation route, which helps young birds when they are first out at sea.
http://en.wikipedia.org/wiki/Diomedeidae
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