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Elegant Tern

Elegant Tern


The Elegant Tern (Sterna elegans or sometimes Thalasseus elegans) is a seabird of the tern family Sternidae. It breeds on the Pacific coasts of the southern USA and Mexico and winters south to Peru, Ecuador and Chile. Surprisingly, this Pacific species has wandered to western Europe as a rare vagrant on a number of occasions, and has interbred with the Sandwich Tern in France. This species breeds in very dense colonies on coasts and islands, and exceptionally inland on suitable large freshwater lakes close to the coast. It nests in a ground scrape and lays one to two eggs. Unlike some of the smaller white terns, it is not very aggressive toward potential predators, relying on the sheer density of the nests (often only 20-30cm apart) and nesting close to other more aggressive species such as Heermann's Gulls to avoid predation. The Elegant Tern feeds by plunge-diving for fish, almost invariably from the sea, like most Sterna terns. It usually dives directly, and not from the "stepped-hover" favoured by the Arctic Tern. The offering of fish by the male to the female is part of the courtship display. This is a medium-large tern, with a long, slender orange bill, pale grey upperparts and white underparts. Its legs are black. In winter, the forehead becomes white. Juvenile Elegant Terns have a scalier pale grey back. The call is a characteristic loud grating noise like a Sandwich Tern. This bird could be confused with the Royal Tern, but the latter species is larger and thicker-billed and shows more white on the forehead in winter. Out of range, it can also be easily confused with the Lesser Crested Tern. It is marginally paler above than the Lesser Crested Tern with a white (not grey) rump, and has a slightly longer, more slender bill. See also Orange-billed tern. Category:Sterna

Seabird

Seabirds are birds that spend much of their lives, outside the breeding season at least, at sea. Whilst the 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 adaptions. Some seabird species, such as the albatrosses and petrels are truly pelagic, breeding on sea cliffs and small islands, and wintering on the open ocean. They are totally dependent on the sea for food. Other species such as the auks and cormorants tend to be more coastal. Some seabird species are marine for only part of the year, nesting inland in marshes and on lakes. Seabirds live longer, breed later and have fewer young than other birds do, but they invest a great deal of time in those young that they do have. Most species nest in colonies, which can vary in size from a few dozen birds to many millions. They are famous for undertaking long annual migrations, crossing the equator or circumnavigating the earth in some cases. They feed both at the ocean's surface and below it, and even feed on each other. Seabirds and humans have a long history together, they have provided food to hunters, guided fishermen to fishing stocks and sailors to land. Many species are currently threatened by human activities, and conservation efforts are underway to preserve them. conservation

Classification of species as seabirds

There exists no one definition of which groups, families and species are seabirds, and most definitions are in some way arbitrary. In the words of two seabird scientists "The one common characteristic that all seabirds share is that they feed in saltwater; but, as seems to be true with any statement in biology, some do not" (Schreiber & Burger 2002). However by convention the penguins, tubenoses, all the Pelecaniformes except the darters, and some of the Charadriiformes (the skuas, gulls, terns, auks and skimmers) are all considered 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 included by some authors, although they are usually treated as waterbirds. Although there are a number of sea ducks in the family Anatidae which are truly marine, 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, but are also not treated as seabirds.

Evolution and fossil record of seabirds

Seabirds, by virtue of living in a geologically depositional environment (that is, in the sea where sediments are readily laid down) are well represented in the fossil record. They are first known to occur in the Cretaceous era, the earliest being the Hesperornithiformes, like Hesperornis regalis, a flightless loon-like seabird that dove in a similar fashion to loons and cormorants (using its feet to move underwater) but had a beak filled with sharp teeth. loon While Hesperornis is not thought to have left descendants, the earliest extant seabirds also occurred in the Cretaceous, with a species called Tytthostonyx glauconiticus, which has been placed in the Procellariiformes. In the Paleogene the seas were dominated by early Procellariidae, giant penguins and two extinct families, the Pelagornithidae and the Plotopteridae (a group of large seabirds that looked like the penguins). Modern genera began their wide radiation in the Miocene although the genus Puffinus (which includes today's Manx Shearwater and Sooty Shearwater) dates back to the Oligocene.

Characteristics of seabirds

Adaptations to life at sea

Seabirds have made numerous adaptations to living on and feeding in the sea. Wing morphology has been shaped by the niche an individual species or family has evolved, so that looking at a wing's shape and loading can tell a scientist about its life feeding behaviour. Longer wings and low wing loading are typical of more pelagic species, whilst diving species have shorter wings. Species such as the Wandering Albatross, which forage over huge areas of sea, have almost lost the ability for powered flight and are dependent on a type of gliding called static soaring (where the wind deflected by waves provides lift). Seabirds also almost always have webbed feet, both to aid movement on the surface as well as used for diving in some species. The Procellariiformes are also unusual amongst birds in using a sense of smell (olfaction) in order to find widely distributed food in a vast ocean. Salt glands are used by seabirds to deal with the salt they ingest by drinking and feeding (particularly on crustaceans), and help them osmoregulate. The excretions from these glands (positioned in the head of the birds and emerging from the nasal cavity) are almost pure NaCl. NaCl With the exception of the cormorants, all seabirds have waterprooof plumage in common with most other birds, however unlike terrestrial birds they have far more feathers protecting their bodies. This dense plumage is better able to protect the bird from getting wet, and cold is kept out by a dense layer of down feathers. The cormorants allow water to soak their feathers as it allows them to swim without fighting the buoyancy that retaining air in the feathers causes, the cost of this is the need to dry out the feathers one they return to land. The plumage of most seabirds is less colourful than that of landbirds, mostly restricted to variations of black, white or grey. A few species sport colourful plumes (like the tropicbirds or some penguins), but the majority of colour in seabirds comes from the bills and legs. The plumage of seabirds is thought in many cases to be for camoflage, both defensive (the colour of US Navy battleships is the same as that of Antarctic Prions!), and aggressive (the white underside possessed by many seabirds helps hide them from prey below them).

Seabird feeding

Seabirds evolved to exploit different food resources on the world's seas and oceans, and to a great extent their physiology and behaviour have been shaped by their diet. These evolutionary forces have often caused species in different families and even orders to evolve similar strategies, and adaptations, to the same problems, leading to remarkable convergent evolution, such as that between auks and penguins. There are four basic feeding strategies, or ecological guilds, for at sea feeding, surface feeding, pursuit diving, plunge diving, and predation of higher vertebrates; within these guilds there are multiple variations on the theme.

Surface feeding

Many seabirds feed on the ocean's surface, as the action of marine currents often concentrates food such as krill, fish, squid or other prey items within reach of a dipped head. The distribution of prey on the sea's surface is often very patchy, some areas have large concentrations of food, while vast areas have none at all, so it is no coincidence that the species that exploit this resource are amongst the best fliers of any of the seabirds, including the greatest traveler of all, the albatrosses. albatross Surface feeding itself can be broken up into two different approaches, surface feeding while flying (for example as practiced by skimmers, frigate-birds and some storm-petrels) and surface feeding whilst swimming (examples of which are fulmars, gulls, many shearwaters and gadfly petrels. Surface feeders in flight include some of the most acrobatic of seabirds, either snatching morsels from the water (as do friagte-birds and some terns), or 'walking' on the water's surface, as do the storm-petrels. Another seabird family that does not land while feeding is the skimmer, which has a unique method; skimmers fly along the surface with the lower mandible in the water, this shuts automatically when the bill touches something in the water. The skimmer's bill relfects its unusual lifestlye, with the lower mandible uniquely being longer than the upper one. Surface feeders that swim often have unique bills, adapted for their specific prey. Prions have special bills with filters called lamellae to filter out plankton from mouthfulls of water, and many albatross and petrels have hooked bills to snatch fast moving. Gulls have more generalised bills that reflect their more opportunistic lifestyle.

Pursuit diving

plankton Pursuit diving exerts greater pressures (both evolutionary and physiological) on seabirds, but the reward is a greater area to feed in than is available to surface feeders. Propulsion underwater can be provided by wings (as used by penguins, auks, diving petrels, and some petrels), or feet (as used by cormorants (as well as grebes and divers and several types of fish-eating ducks). Wing-propelled divers generally are faster than feet-propelled divers. In both cases the use of wings or feet for diving has limited its utility in other situations, divers and grebes walk with extreme difficulty (if at all), penguins cannot fly, and auks have sacrificed flight to a great extent for underwater diving. For example, the razorbill (an Atlantic auk) requires 64% more energy to fly as an equivalent petrel. However no generalised rule exists in biology without being broken, and recent research using capilllary depth recorders has shown that many species of albatross, petrel and shearwater are actually reasonably good divers as well as excellent fliers. Some albatross species are capable of diving as far as 13m, and the Short-tailed Shearwater has been recorded below 70m! Of all the wing-propelled pursuit divers the best 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. The poor flying ability many pursuit divers are more confined 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 from flight into the water. This uses less energy than dedicated pursuit divers, and they are able to use more spread out food resources, for example 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 use it but do so with less skill and from lower heights. In Brown Pelicans the skills of plunge diving take several years to develop fully, once mature they can dive from 20 m above the water's surface, shifting the body before impact to avoid injury. Plunge divers are restricted in their hunting grounds to clear waters that afford a view of their prey from the air, and are the dominant guild in the tropics. Some plunge divers (as well as surface feeders) are dependent on predatory fish like tuna and dolphins to push shoaling fish up towards the surface.

Kleptoparasitism, scavenging and other seabirds

dolphinThis catch-all category refers to other seabird strategies that involve the next trophic level up. Kleptoparasites are seabirds that make a living (or more often a part of their living) stealing food of other seabirds. Most famously frigate-birds and skuas engage in this behaviour, although gulls, terns and other species will steal food opportunistically. The nocturnal nesting behaviour of many seabirds has been interpreted as arising due to pressure from this arial piracy. Many species of gull will also feed on seabird and sea mammal carrion when the opportunity arises, as will giant petrels. Some species will also feed on other seabirds, for example gulls, skuas and giant petrels will often take eggs, chicks and even small seabirds on nesting colonies.

Life-history

Seabirds' life-histories are dramatically different from those of land birds. In general they are K-selected, live much longer (anywhere between 20 and 60 years), they delay breeding for longer (for up to 10 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), and many species (like the tubenoses and sulids), only one egg a year. There is also a long period of care for the young, extending for as long as six months, among the longest for birds. For example, once Common Guillemot chicks fledge they remain with the male parent for several months at sea. This life-history strategy has probably evolved both in response to the challenges of living at sea and the relative lack of predation compared to that of land living birds. Because of the greater investment in raising the young and because foraging for food may occur far from the nest site, in most species both parents participate in caring for the young and pairs are typically at least seasonally monogamous.

Seabird colonies

:See also Seabird colony Seabird colony 95% of seabirds (not including the grebes and loons) are colonial, and seabird colonies are amongst the largest in the world, and provide one of Earth's great wildlife spectacles. Colonies of over a million birds have been recorded, both in the tropics (such as Kiritimati in the Pacific) and in the polar latitudes (as found in Antarctica). Seabird colonies occur exclusively for the purpose of breeding, non-breeding birds will only collect together outside the breeding season in areas where prey species are densely aggregated. Seabird colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed like a murre colony. In most seabird colonies several different species will nest on the same colony, often exhibiting some niche separation. Seabirds can nest in trees (if any are available), on the ground (with or without nests), on cliffs, in burrows under the ground and in rocky crevices. Many seabirds show remarkable site fidelity, returning to the same burrow, nest or site for many years, and they will defend that site from rivals with great vigour. This increases breeding success, provides an place for returning mates to reunite, and reduces the costs of prospecting for a new site. Young adults breeding for the first time usually return to their natal colony, and often nest very close to where they hatched. Colonies are thought to provide protection to seabirds, which are often very clumsy on land, and are usually situated on islands where land mammals have difficulty getting to. Coloniality often arises in other 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 disadvantages to colonial life, particularly the spread of disease. 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.

Seabird migration

diseaseLike 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 spend the Austral summer of Antarctica. Other species also undertake trans-equatorial trips, both from the north to the south, like Elegant Terns, which nest off Baja California and feed off Peru in the Humboldt Current, or the two species of marine phalaropes, the Grey Phalarope and the Red-necked Phalarope; to those that undertake south to north, like the Sooty Shearwaters that nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific. Other species also migrate shorter distances away from the breeding sites, their distribution at sea determined by the avaliablity of food. After fledging, juvenile birds often disperse further than adults to, and to different areas, and are commonly sighted far from a species' normal range. Some species, such as the auks, do not have a concerted migration effort, but drift southwards as the winter approaches. Other species, such as some of the storm-petrels, diving petrels and cormorants, never disperse at all, staying near the breeding colonies year round.

Away from the sea

Whilst the definition of seabirds suggests that the birds in question spend their lives on the 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. The Marbled Murrelet nests inland in old-growth forest, seeking ancient conifers with large branches to nest on. Other species, such as the California Gull nest and feed inland on lakes, and then move to the coasts in the winter. Some cormorants, 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 gulls, cities and argicultural land. Some seabirds, principally those that nest in tundra like skuas and phalaropes, will migrate across 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 large numbers to exhausted adults after a large storm, an event known as a wreck, where they are prized sightings for birders.

Seabirds and humans

Seabirds and fisheries

Seabirds have had a long association with both fisheries and sailors. Both fisheries and seabirds have drawn benefits and disadvantages from the long relationship. Fishermen have long used seabirds as indicators of both fish shoals, underwater banks that might indicate fish stocks, and of potential land. In fact the known association of seabirds with land was instrumental in allowing the Polynesians to locate tiny landmasses in the Pacific. Seabirds also 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, although longlining fisheries also have to deal with bait-stealing. There have been claims of prey-depletion by seabirds of fishery stocks, and while there is some small evidence of this, the effects of seabirds are considered smaller than that of marine mammals and predatory fish (like tuna). tunaSome species and families of seabirds have benefited from fisheries, particularly from discarded fish and offal. These discards comprise 30% of the food of seabirds in the North Sea, for example, and comprise up to 70% of the total food of some species. 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. 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 albatross are a source of increasing concern to conservationists. The by-catch of seabirds entangled in nets or hooked on fishing lines has had a big impact on seabird numbers, for example an estimated 44,000 albatross are hooked each year on tuna lines set out by Japanese fleets. Overall many hundreds of thousands or possibly millions 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 Albatross are known to still exist). Seabirds also suffer when stocks of fish are overfished.

Exploitation of seabirds

The hunting of seabirds, and the collecting of seabird eggs, have contributed to the declines of many species of seabirds, as well as the extinction of one species, the Great Auk. Seabirds have been hunted for food by many coastal people over time, and have become locally extinct in many places. In particular at least 20 species out of 29 no longer breed on Easter Island. In the 19th century the hunting of seabirds for fat deposits and feathers for the millinery trade reached industrial levels. In the Falkland Islands hundreds of thousands of penguins were harvested for their oil each year. Seabird eggs have also long been an important source of food for sailors undertaking long sea voyages, as well as being taken when cities grow in areas near a colony. Eggers from San Francisco took almost half a millions eggs a year from the Farallon Islands in the mid 19th century, a period in the island's history from which the seabird species are still recovering. Both hunting and egging continue today, although not at the level that occurred in the past, and generally in a more controlled level. For example, the Maori of Stewart Island/Rakiura continue to harvest the chicks of the Sooty Shearwater as they have done so for centuries, using traditional methods (called kaitiakitanga) to manage the harvest, but now also work with the University of Otago in studying the populations.

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 overall on small isolated islands, have lost many predator defense behaviour. Feral cats are capable of taking out seabirds as large as albatross, and many introduced rodents, such as the Pacific rat can take eggs hidden in burrows. Introduced goats, cattle, rabbits and other herbivores can also lead to problems, particularly when species need vegetation to protect or shade their young. Disturbance of breeding colonies by people is often a problem as well, visitors, even well meaning tourists, can flush a colony leaving chicks and eggs vulnerable to predators. tourist The build up of toxins and pollutants in seabirds is also a concern. Seabirds, being apex predators, suffered from the ravages of DDT until they were banned, and concern continues with other pollutants, for example Forster's Terns in San Francisco were found to have high levels of polybrominated diphenyl ethers (PBDEs), used as fire retardants. Oil spills are also a major 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.

Seabird conservation

The threats faced by seabirds have not gone unnoticed by scientists or the conservation movement. As early as 1903 Theodore Roosevelt was convinced of the need to declare Pelican Island in Florida a National Wildlife Refuge to protect the bird colonies (including the nesting Brown Pelicans), a few years later in 1909 he protected the Farallon Islands. Today many important seabird colonies are given some measure of protection, from Heron Island in Australia to Triangle Island in British Columbia. The field of island restoration, developed initially by New Zealand, is removing exotic invaders from increasingly large islands. Feral cats have been removed from Wake Island, rabbits from Laysan, and rats from Campbell Island. The removal of these introduced species has lead to increases in surviving species and even the return of expirated ones. The plight of albatross and other large seabirds, as well as other marine creatures, being taken as by-catch by longline fisheries, has been taken up by a large number of NGOs (including BirdLife International and the RSPB). This lead to Agreement on the Conservation of Albatrosses and Petrels signed as part of the Convention on Migratory Species, a legally binding treaty designed to protect these threatened species (it has currently been ratified by eight countries, Argentina, Australia, Ecuador, New Zealand, Spain, France, Peru and South Africa.

Seabirds in culture

South AfricaMany seabirds, living far out to sea and breeding in isolated colonies, have been and still are very obscure and unknown, even to scientists. Some seabirds have made the break into popular consciousness, most particularly the albatross and gulls. 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. The albatross have been described as the most legendary of birds, and have a variety of myths and legends associated with them, and even today it is widely considered unlucky to harm them (though unfortunately not on long-lining boats). These tales are also associated with Samuel Taylor Coleridge's famous poem, the Rime of the Ancient Mariner. In a similar fashion, it was also considered unlucky to touch a storm-petrels, especially one that has landed on the ship. Gulls are one of the most commonly seen seabirds, given their use of human made habitats (such as cities and dumps), and their often fearless nature. They therefore also have made it into the popular consciousness, if only as the 'flying rats' berated in Finding Nemo. They have been used metaphorically, as in Jonathan Livingston Seagull, by Richard Bach, or to denote a closeness to the sea, such as their use in the Lord of the Rings, both in the insignia of Gondor, and therefore Númenor (used in the design of the film), and to call Legolas to, and across, the sea.

Seabird families

The following are the groups of birds normally classed as seabirds. Sphenisciformes (Antarctic and southern waters; 16 species)
- Spheniscidae penguins Procellariiformes (Tubenoses: pan-oceanic and pelagic; 93 species)
- Diomedeidae albatross
- Procellariidae fulmars, prions, shearwaters, gadfly and other petrels
- Pelacanoididae diving petrels
- Hydrobatidae storm-petrels (see also petrel) 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


- del Hoyo, Josep, Elliott, Andrew & Sargatal, Jordi (1992). Handbook of Birds of the World Vol 1. Barcelona:Lynx Edicions, ISBN 84-87334-10-5
- Gaston, Anthony J. & Jones, Ian L. (1998). The Auks Oxford:Oxford University Press, ISBN 0-19-854032-9
- Gaston, Anthony J. (2004). Seabirds: A Natural History New Haven:Yale University Press, ISBN 0-300-10406-5
- Löfgren, Lars (1984). Ocean Birds, Gothenburg:Nordbok, ISBN 0-394-53101-9
- Schreiber, Elizabeth A. & Burger, Joanne.(2001.) Biology of Marine Birds, Boca Raton:CRC Press, ISBN 0-8493-9882-7

External links


- [http://www.otago.ac.nz/titi/default.html Project Titi; a collaboration between the Maori of Stewart Island and the University of Otago to manage Sooty Shearwater harvests]
- [http://www.birdlife.org/action/campaigns/save_the_albatross/index.html BirdLife International; Save the Albatross Campaign]
- [http://www.marineornithology.org/ Marine Ornithology, the Journal of Seabird Science and Conservation]
- ja:海鳥

Tern



- Sterna

  - (Gelochelidon)

  - (Hydroprogne)

  - (Thalasseus)

- Chlidonias

- Phaetusa

- Anous

- Procelsterna

- Gygis

- Larosterna ]] Terns are seabirds in the family Sternidae, previously considered a subfamily Sterninae of the gull family Laridae. They are less closely related to the waders, auks and skimmers. They have a worldwide distribution. Most terns belong to the large genus Sterna, with the other genera being small, though some authorities split the genus Sterna into several smaller genera (see list, below). Many terns breeding in temperate zones are long-distance migrants, and the Arctic Tern probably sees more daylight than any other creature, since it migrates from its northern breeding grounds to Antarctic waters. One Arctic Tern, ringed as a chick (not yet able to fly) on the Farne Islands off the Northumberland coast in eastern Britain in summer 1982, reached Melbourne, Australia in October 1982, a sea journey of over 22,000 km (14,000 miles) in just three months from fledging - an average of over 240 km per day, and one of the longest journeys ever recorded for a bird. They are in general medium to large birds, typically with grey or white plumage, often with black markings on the head. They have longish bills and webbed feet. They are lighter bodied and more streamlined than gulls, and look elegant in flight with long tails and long narrow wings. Terns in the genus Sterna have deeply forked tails, those in Chlidonias and Larosterna shallowly forked tails, while the noddies (genera Anous, Procelsterna, Gygis) have unusual 'notched wedge' shaped tails, the longest tail feathers being the middle-outer, not the central nor the outermost. Most terns (Sterna and the noddies) hunt fish by diving, often hovering first, but the marsh terns (Chlidonias) pick insects of the surface of fresh water. Terns only glide infrequently; a few species, notably Sooty Tern, will soar high above the sea. Apart from bathing, they only rarely swim, despite having webbed feet. Terns are generally long-lived birds, with several species now known to live in excess of 25-30 years.

Classification & species list


- Genus Sterna
- Subgenus Gelochelidon
  - Gull-billed Tern, Sterna nilotica (Gelochelidon nilotica)
- Subgenus Hydroprogne - Caspian Tern.
  - Caspian Tern, Sterna caspia (Hydroprogne caspia)
- Subgenus Thalasseus - crested terns.
  - Royal Tern, Sterna maximus (Thalasseus maximus)
  - Greater Crested Tern or Swift Tern, Sterna bergii (Thalasseus bergii)
  - Chinese Crested Tern, Sterna bernsteini (Thalasseus bernsteini)
  - Elegant Tern, Sterna elegans (Thalasseus elegans)
  - Lesser Crested Tern Sterna bengalensis (Thalasseus bengalensis)
  - Sandwich Tern, Sterna sandvicensis (Thalasseus sandvicensis)
- Subgenus Sterna - typical white terns
  - River Tern Sterna aurantia
  - Roseate Tern, Sterna dougallii
  - White-fronted Tern, Sterna striata
  - Black-naped Tern, Sterna sumatrana
  - South American Tern, Sterna hirundinacea
  - Common Tern Sterna hirundo
  - Arctic Tern Sterna paradisaea
  - Antarctic Tern, Sterna vittata
  - Kerguelen Tern, Sterna virgata
  - Forster's Tern, Sterna forsteri
  - Trudeau's Tern, Sterna trudeaui
  - White-cheeked Tern Sterna repressa
  - Black-bellied Tern, Sterna acuticauda
  - Black-fronted Tern, Sterna albostriata
- Subgenus Sternula - little tern group.
  - Little Tern Sterna albifrons
  - Saunders' Tern, Sterna saundersi (Often considered conspecific with Little Tern)
  - Least Tern Sterna antillarum (Often considered conspecific with Little Tern)
  - Yellow-billed Tern, Sterna superciliaris
  - Peruvian Tern, Sterna lorata
  - Fairy Tern, Sterna nereis
  - Damara Tern, Sterna balaenarum
- Subgenus Haliplana - "brown-backed" terns.
  - Aleutian Tern, Sterna aleutica
  - Grey-backed Tern, Sterna lunata
  - Bridled Tern, Sterna anaethetus
  - Sooty Tern, Sterna fuscata
- Chlidonias - marsh terns.
  - Whiskered Tern Chlidonias hybridus
  - White-winged Tern or White-winged Black Tern Chlidonias leucopterus
  - Black Tern Chlidonias niger
- Phaetusa - Large-billed Tern.
  - Large-billed Tern Phaetusa simplex
- Anous, Procelsterna, Gygis - noddies. A tropical group, characterised by the notch-wedge shaped (not forked) tail; coastal and pelagic oceanic.
  - Brown Noddy Anous stolidus
  - Black Noddy Anous minutus
  - Lesser Noddy, Anous tenuirostris
  - Blue Noddy, Procelsterna cerulea
  - Grey Noddy, Procelsterna albivitta
  - White Tern, Gygis alba
- Larosterna - Inca Tern.
  - Inca Tern Larosterna inca

Other usage

In North East Scotland people who are talking about "the Tern" are quite likely referring to an oil field or oil platform operated in the Shetland basin by Shell/ExxonMobil. All of this consortium's UK assets are referred to by the names of various seabirds (though when they have bought assets from other operators, they have sometimes retained existing names). Category:Terns

Pacific

:For other meanings of Pacific, see Pacific (disambiguation). The Pacific Ocean (from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan) is the world's largest body of water. It encompasses a third of the Earth's surface, having an area of 179.7 million km² (69.4 million sq miles). Extending approximately 15,500 km (9,600 miles) from the Bering Sea in the Arctic to the icy margins of Antarctica's Ross Sea in the south (although the Antarctic regions of the Pacific are sometimes described as part of the circumpolar Southern Ocean)the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 km (12,300 miles) from Indonesia to the coast of Colombia. The western limit of the ocean is often placed at the Strait of Malacca. The lowest point on earth—the Mariana Trench—lies some 10,911 m (35,797 ft) below sea level. The Pacific contains about 25,000 islands (more than the total number in the rest of the world's oceans combined), the majority of which are found south of the equator. (See: Pacific Islands.) Along the Pacific Ocean's irregular western margins lie many seas, the largest of which are the Celebes Sea, Coral Sea, East China Sea, Sea of Japan, South China Sea, Sulu Sea, Tasman Sea, and Yellow Sea. The Straits of Malacca joins the Pacific and the Indian Oceans on the west, and the Straits of Magellan links the Pacific with the Atlantic Ocean on the east. As the Pacific straddles the ±180° longitude where East becomes West, the Asian side of the ocean (where latitudes are E) is correctly referred to as East Pacific and the opposite side (eastwards) where latitudes are W is the West Pacific. To retain the popular "left is western" and "right is eastern" means of reference, the Western Pacific is thus the East Pacific and the Eastern Pacific the West Pacific. The International Date Line follows the ±180° longitude to the greater part of its North-South demarcation but veers far eastwards around Kiribati (Caroline Island, which, not coincidentally, was renamed Millennium Island) and westwards round the Aleutian Islands as can be seen on the map at International Date Line. For most of Ferdinand Magellan's voyage from the Straits of Magellan to the Philippines, the Portuguese explorer indeed found the ocean peaceful. However, the Pacific is not always peaceful. Many typhoons and hurricanes batter the islands of the Pacific and the lands around the Pacific rim are full of volcanoes and often rocked by earthquakes. Tsunamis, caused by underwater earthquakes, have devastated many islands and wiped out whole towns. Tsunami

Ocean bottom

The ocean floor of the central Pacific basin is relatively uniform, an abyssal plain with a mean depth of about 4270 m (14,000 ft). The major irregularities in the basin are the extremely steep-sided, flat-topped submarine peaks known as seamounts. The western part of the floor consists of mountain arcs that rise above the sea as island groups, such as the Solomon Islands and New Zealand, and deep oceanic trenches, such as the Mariana Trench, the Philippine Trench, and the Tonga Trench. Most of the trenches lie adjacent to the outer margins of the wide western Pacific continental shelf. Along the eastern margin of the Pacific Basin is the East Pacific Rise, which is a part of the worldwide mid-oceanic ridge. About 3000 km (1800 miles) across, the rise stands about 3 km (2 miles) above the adjacent ocean floor. Because a relatively small land area drains into the Pacific, and because of the ocean's immense size, most sediments are authigenic or pelagic in origin. Authigenic sediments include montmorillonite and phillipsite. Pelagic sediments derived from seawater include pelagic red clays and the skeletal remains of sea life. Terrigenous sediments eroded from land masses are confined to narrow marginal bands close to land.

Elevation extremes


- lowest point: -10,924 m (-35,840 ft). at the bottom of the Mariana Trench
- highest point: 0 m (0 ft), sea level.

Water characteristics

Water temperatures in the Pacific vary from freezing in the poleward areas to about 29°C (84°F) near the equator. Salinity also varies latitudinally. Water near the equator is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. Poleward of the temperate latitudes salinity is also low, because little evaporation of seawater takes place in these frigid areas. The surface circulation of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific Gyre) and anti-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current. Turning eastward at about 45°N, the Kuroshio forks and some waters move northward as the Aleutian Current, while the rest turn southward to rejoin the North Equatorial Current. The Aleutian Current branches as it approaches North America and forms the base of an anti-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled slow, south-flowing California Current. The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50°S, and joins the main westerly circulation of the Southern Pacific, which includes the Earth-circling Antarctic Circumpolar Current. As it approaches the Chilean coast, the South Equatorial Current divides; one branch flows around Cape Horn and the other turns north to form the Peru or Humboldt Current.

Climate

Only the interiors of the large land masses of Australia, New Guinea, and New Zealand escape the pervasive climatic influence of the Pacific. Within the area of the Pacific, five distinctively different climatic regions exist: the mid-latitude westerlies, the trades, the monsoon region, the typhoon region, and the doldrums. Mid-latitude westerly air streams occur in both northerly and southerly latitudes, bringing marked seasonal differences in temperature. Closer to the equator, where most of the islands lie, steadily blowing trade winds allow for relatively constant temperatures throughout the year of 21-27°C (70-81°F). The monsoon region lies in the far western Pacific between Japan and Australia. Characteristic of this climatic region are winds that blow from the continental interior to the ocean in winter and in the opposite direction in summer. Consequently, a marked seasonality of cloudiness and rainfall occurs. Typhoons often cause extensive damage in the west and southwest Pacific. The greatest typhoon frequency exists within the triangle from southern Japan to the central Philippines to eastern Micronesia. Although more poorly defined than the other climatic regions, two major doldrum areas lie within the ocean, one located off the western shores of Central America and the other within the equatorial waters of the western Pacific. Both areas are noted for their high humidity, considerable cloudiness, light fluctuating winds, and frequent calms.

Geology

The Andesite Line is the most significant regional distinction in the Pacific. It separates the deeper, basic igneous rock of the Central Pacific Basin from the partially submerged continental areas of acidic igneous rock on its margins. The Andesite Line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand. The dissimilarity continues northeastward along the western edge of the Albatross Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand—all eastward extensions of the continental blocks of Australia and Asia—lie outside the Andesite Line. Within the closed loop of the Andesite Line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Central Pacific Basin. It is here that basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the Andesite Line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism.

Landmasses

The largest landmass entirely within the Pacific Ocean is the island of New Guinea— the second largest in the world. Almost all of the smaller islands of the Pacific lie between 30°N and 30°S, extending from South-east Asia to Easter Island; the rest of the Pacific Basin is almost entirely submerged. The great triangle of Polynesia, connecting Hawaii, Easter Island, and New Zealand, encompasses the island arcs and clusters of the Cook, Marquesas, Samoa, Society, Tokelau, Tonga, and Tuamotu islands. North of the equator and west of the international date line are the numerous small islands of Micronesia, including the Caroline Islands, the Marshall Islands, and the Mariana Islands. In the southwestern corner of the Pacific lie the islands of Melanesia, dominated by New Guinea. Other important island groups of Melanesia include the Bismarck Archipelago, Fiji, New Caledonia, the Solomon Islands, and Vanuatu. Islands in the Pacific Ocean are of four basic types: continental islands, high islands, coral reefs, and uplifted coral platforms. Continental islands lie outside the Andesite Line and include New Guinea, the islands of New Zealand, and the Philippines. These islands are structurally associated with the nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands. The third and fourth types of islands are both the result of coralline island building. Coral reefs are low-lying structures that have built up on basaltic lava flows under the ocean's surface. One of the most dramatic is the Great Barrier Reef off northeastern Australia. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Examples include Banaba (formerly Ocean Island) and Makatea in the Tuamotu group of French Polynesia.

History and economy

See the Oceania article for information on one set of the Pacific Island states listed below here. Important human migrations occurred in the Pacific in prehistoric times, most notably those of Polynesians from Tahiti to Hawaii and New Zealand. The ocean was sighted by Europeans early in the 16th century, first by Vasco Núñez de Balboa (1513) and then by Ferdinand Magellan, who crossed the Pacific during his circumnavigation (1519-1522). In 1564 conquistadors crossed the ocean from Mexico led by Miguel López de Legazpi who sailed to the Philippines and Mariana Islands. For the remainder of the 16th century Spanish influence was paramount, with ships sailing from Spain to the Philippines, New Guinea, and the Solomons. The Manila Galleons linked Manila and Acapulco. During the 17th century the Dutch, sailing around southern Africa, dominated discovery and trade; Abel Janszoon Tasman discovered (1642) Tasmania and New Zealand. The 18th century marked a burst of exploration by the Russians in Alaska and the Aleutian Islands, the French in Polynesia, and the British in the three voyages of James Cook (to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest). Growing imperialism during the 19th century resulted in the occupation of much of Oceania by Great Britain and France, followed by the United States. Significant contributions to oceanographic knowledge were made by the voyages of the HMS Beagle in the 1830s, with Charles Darwin aboard; the HMS Challenger during the 1870s; the U.S.S. Tuscarora (1873-76); and the German Gazelle (1874-1876). Although the United States took the Philippines in 1898, Japan controlled the western Pacific by 1914, and occupied many other islands during World War II. By the end of that war the U.S. Pacific Fleet was the virtual master of the ocean. Seventeen independent states are located in the Pacific: Australia, Fiji, Japan, Kiribati, Marshall Islands, Micronesia, Nauru, New Zealand, Palau, Papua New Guinea, the Philippines, Samoa, Solomon Islands, Republic of China (Taiwan), Tonga, Tuvalu, and Vanuatu. Eleven of these nations have achieved full independence since 1960. The Northern Mariana Islands are self-governing with external affairs handled by the United States, and Cook Islands and Niue are in similar relationships with New Zealand. Also within the Pacific are the U.S. state of Hawaii and several island territories and possessions of Australia, Chile, Ecuador, France, Japan, New Zealand, the United Kingdom, and the United States. The exploitation of the Pacific's mineral wealth is hampered by the ocean's great depths. In shallow waters of the continental shelves off the coasts of Australia and New Zealand, petroleum and natural gas are extracted, and pearls are harvested along the coasts of Australia, Japan, Papua New Guinea, Nicaragua, Panama, and the Philippines, although in sharply declining volume. The Pacific's greatest asset is its fish. The shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish. In 1986, the member nations of the South Pacific Forum declared the area a nuclear-free zone in an effort to halt nuclear testing and prevent the dumping of nuclear waste there.

Ports and harbours


- Acapulco (Mexico)
- Anchorage (United States)
- Auckland (New Zealand)
- Brisbane (Australia)
- Callao (Peru)
- Hong Kong (Hong Kong (China (PRC)))
- Honolulu (United States)
- Kobe (Japan)
- Long Beach (United States)
- Los Angeles (United States)
- Panama City (Panama)
- Portland (Oregon) (United States)
- Prince Rupert (Canada)
- San Diego (United States)
- San Francisco (United States)
- Sapporo (Japan)
- Seattle (United States)
- Shanghai (China (PRC))
- Sydney (Australia)
- Taipei (China (ROC))
- Vancouver (Canada)
- Victoria (Canada)
- Vladivostok (Russia)
- Yokohama (Japan)

Bibliography


- Barkley, R.A., Oceanographic Atlas of the Pacific Ocean (1969)
- Cameron, I., Lost Paradise (1987)
- Couper, A., Development in the Pacific Islands (1988)
- Crump, D.J., ed., Blue Horizons (1980)
- Gilbert, John, Charting the Vast Pacific (1971)
- Lower, J. Arthur, Ocean of Destiny: A Concise History of the North Pacific, 1500-1978 (1978)
- Oliver, D.L., The Pacific Islands, 3nd ed. (1989)
- Ridgell, R., Pacific Nations and Territories, 2nd ed. (1988)
- Soule, Gardner, The Greatest Depths (1970)
- Spate, O.H., Paradise Found and Lost (1988)
- Terrell, J.E., Prehistory in the Pacific Islands (1986). :Based on public domain text from US Naval Oceanographer

External links


- [http://www.epic.noaa.gov/epic/ewb/ EPIC Pacific Ocean Data Collection] Viewable on-line collection of observational data
- [http://dapper.pmel.noaa.gov/dchart/ NOAA In-situ Ocean Data Viewer] Plot and download ocean observations
- [http://www.mapsouthpacific.com/ Map South Pacific]
- [http://www.oscar.noaa.gov/datadisplay/ NOAA Ocean Surface Current Analyses - Realtime (OSCAR)] Near-realtime Pacific Ocean Surface Currents derived from satellite altimeter and scatterometer data
- [http://floats.pmel.noaa.gov/floats/ NOAA PMEL Argo profiling floats] Realtime Pacific Ocean data
- [http://www.pmel.noaa.gov/tao/jsdisplay/ NOAA TAO El Nino data] Realtime Pacific Ocean El NIno buoy data
- [http://www.southpacific.org/ South Pacific Organizer] Category:Oceans
- zh-min-nan:Thài-pêng-iûⁿ ko:태평양 ja:太平洋 simple:Pacific Ocean th:มหาสมุทรแปซิฟิก

USA

:For alternative meanings, see the disambiguation page for US, USA, United States, or American. The United States of America is a federal democratic republic situated primarily in central North America. It comprises 50 states and one federal district, and has several territories. It is also referred to, with varying formality, as the United States, the U.S., the U.S.A., the States, or simply and most commonly, America. The official founding date of the United States is July 4, 1776, when the Second Continental Congress—representing thirteen British colonies—adopted the Declaration of Independence. However, the structure of the government was profoundly changed in 1788, when the states replaced the Articles of Confederation with the United States Constitution. The date on which each of the fifty states adopted the Constitution is typically regarded as the date that state "entered the Union" (became part of the United States). Since the mid-20th century, following World War II, the United States has emerged as a dominant global influence in economic, political, military, scientific, technological, and cultural affairs.

Geography and climate

The United States shares land borders with Canada (to the north) and Mexico (to the south), and territorial water boundaries with Canada, Russia, the Bahamas, and numerous smaller nations. It is otherwise bounded by the Pacific Ocean and the Bering Sea, in the west; the Arctic Ocean, in the northernmost areas; and the Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea, in the eastern and southeastern areas. Forty-eight of the states are in the single region between Canada and Mexico; this group is referred to, with varying precision and formality, as the continental or contiguous United States, sometimes abbreviated CONUS, and as the Lower 48. Alaska, which is not included in the term contiguous United States, is at the northwestern end of North America, separated from the Lower 48 by Canada. The archipelago of Hawaii is in the Pacific Ocean. The capital city, Washington, District of Columbia is a federal district located on land donated by the state of Maryland. (Virginia also donated land, but it was returned in 1847.) The United States also has overseas territories with varying levels of independence and organization. When inland water is included in the total area, only Russia and Canada are larger than the United States; if inland water is excluded, China ranks third and the U.S. ranks fourth. The United States' total area is 3,718,711 square miles (9,631,418 km²), of which land makes up 3,537,438 square miles (9,161,923 km²) and water makes up 181,273 square miles (469,495 km²). The United States' landscape is one of the most varied among those of the world's nations: among its many features are temperate forestland and rolling hills, on the east coast; mangrove, in Florida; the Great Plains, in the center of the country; the Mississippi–Missouri river system; the Great Lakes, four of the five of which are shared with Canada; the Rocky Mountains, west of the Great Plains; deserts and temperate coastal zones, west of the Rocky Mountains; and temperate rain forests, in the Pacific northwest. Alaska's tundra, and the volcanic, tropical islands of Hawaii add to the geographic diversity. Hawaii The climate varies along with the landscape, from tropical in Hawaii and southern Florida to tundra in Alaska and atop some of the highest mountains. Most of the North and East experience a temperate continental climate, with warm summers and cold winters. Most of the South experiences a subtropical humid climate with mild winters and long, hot, humid summers. Rainfall decreases markedly from the humid forests of the Eastern Great Plains to the semi-arid shortgrass prairies on the high plains abutting the Rocky Mountains. Arid deserts, including the Mojave, extend through the lowlands and valleys of the southwest, from westernmost Texas to California and northward throughout much of Nevada. Some parts of California have a Mediterranean climate. Rainforests line the windward mountains of the Pacific Northwest from Oregon to Alaska.

History

American history started with the migration of people from Asia across the Bering land bridge approximately 12,000 years ago following large animals that they hunted into the Americas. These Native Americans left evidence of their presence in petroglyphs, burial mounds, and other artifacts. It is estimated that 2-9 million people lived in the territory now occupied by the U.S. before European contact, and the subsequent introduction of foreign diseases such as small pox that greatly diminished the native populations. Some advanced societies were the Anasazi of the southwest, who inhabited Chaco Canyon, and the Woodland Indians, who built Cahokia, located near present-day St Louis, a city with a population of 40,000 at its peak in AD 1200. Vikings first visited North America around 1000, but did not settle permanently. Following the discovery voyages of Christopher Columbus around 1492, other Europeans began to explore and settle there. During the 1500s and 1600s, the Spanish settled parts of the present-day Southwest and Florida, founding St. Augustine, Florida in 1565 and Santa Fe (in what is now New Mexico) in 1607. The first successful English settlement was at Jamestown, Virginia, also in 1607. Within the next two decades, several Dutch settlements, including New Amsterdam (the predecessor to New York City), were established in what are now the states of New York and New Jersey. In 1637, Sweden established a colony at Fort Christina (in what is now Delaware), but lost the settlement to the Dutch in 1655. This was followed by extensive British settlement of the east coast. The British colonists remained relatively undisturbed by their home country until after the French and Indian War, when France ceded Canada and the Great Lakes region to Britain. Britain then imposed taxes on the 13 colonies, widely regarded by the colonists as unfair because they were denied representation in the British Parliament. Tensions between Britain and the colonists increased, and the thirteen colonies eventually rebelled against British rule. British Parliament, George Washington (1789-1797).]] In 1776, the 13 colonies split from Great Britain and formed the United States, the world's first constitutional and democratic federal republic, after their Declaration of Independence of that year, and the Revolutionary War (1775 to 1783). The original political structure was a confederation in 1777, ratified in 1781 as the Articles of Confederation. After long debate, this was supplanted by the Constitution in 1789, forming a more centralized federal government. Prior to all these was the Albany Congress in 1754, in which a union was first seriously proposed. From early colonial times, there was a shortage of labor, which encouraged unfree labor, particularly indentured servitude and slavery. In the mid-19th century, a major division occurred in the United States over the issue of states' rights and the expansion of slavery. The northern states had become opposed to slavery, while the southern states saw it as necessary for the continued success of southern agriculture and wanted it expanded to the territories. Several federal laws were passed in an attempt to settle the dispute, including the Missouri Compromise and the Compromise of 1850. The dispute reached a crisis in 1861, when seven southern states seceded1 from the Union and formed the Confederate States of America, leading to the Civil War. Soon after the war began, four more southern states seceded. During the war, Abraham Lincoln issued the Emancipation Proclamation, mandating the freedom of all slaves in states in rebellion, though full emancipation did not take place until after the end of the war in 1865, the dissolution of the Confederacy, and the Thirteenth Amendment took effect. The Civil War effectively ended the question of a state's right to secede, and is widely accepted as a major turning point after which the federal government became more powerful than state governments. Thirteenth Amendment). The title of the painting, from a 1726 poem by Bishop Berkeley, was a phrase often quoted in the era of Manifest Destiny, expressing a widely held belief that civilization had steadily moved westward throughout history. [http://americanart.si.edu/t2go/1lw/1931.6.1.html (more)] ]] During the 19th century, many new states were added to the original 13 as the nation expanded across the continent. Manifest Destiny was a philosophy that encouraged westward expansion in the United States. As the population of the Eastern states grew and as a steady increase of immigrants entered the country, settlers moved steadily westward across North America. In the process, the U.S. displaced most American Indian nations. This displacement of American Indians continues to be a matter of contention in the U.S. with many tribes attempting to assert their original claims to various lands. In some areas American Indian populations were reduced by foreign diseases contracted through contact with European settlers, and US settlers acquired those emptied lands. In other instances American Indians were removed from their traditional lands by force. Though some would say the U.S. was not a colonial power until the Spanish-American War when it acquired Puerto Rico, Guam and the Philippines, the dominion exercised over land in North America the United States claimed is essentially colonial. The Philippines became independent in 1946. During this period, the nation also became an industrial power. This continued into the 20th century, which has been termed "the American Century" because of the nation's overriding influence on the world. The US became a center for innovation and technological development; major technologies that America either developed or was greatly involved in improving include the telephone, television, computer, the Internet, nuclear weapons, nuclear power, aviation, and aeronautics. In addition to the Civil War, another major traumatic experience for the nation was the Great Depression (1929 to 1939). The nation has also taken part in several major foreign wars, including World War I and World War II (in both of which the US later joined the Allies). During the Cold War, the US was a major player in the Korean War and Vietnam War, and, along with the Soviet Union, was considered one of the world's two "superpowers". With the collapse of the Soviet Union, the US emerged as the world's leading economic and military power. Beginning in the 1990s, the United States became very involved in police actions and peacekeeping, including actions in Kosovo, Haiti, Somalia and Liberia, and the first Persian Gulf War driving Iraq out of Kuwait. After attacks on the World Trade Center and the Pentagon on September 11, 2001, the United States and other allied nations found themselves involved in what has come to be called the "War on Terrorism," which has primarily encompassed military actions in both Afghanistan and Iraq.

Government

Iraq of the United States.]]

Republic and suffrage

The United States is an example of a constitutional republic, with a government composed of and operating through a set of limited powers imposed by its design and enumerated in the United States Constitution. Specifically, the nation operates as a presidential democracy. There are three levels of government: federal, state, and local. Officials of each of these levels are either elected by eligible voters via secret ballot or appointed by other elected officials. Americans enjoy almost universal suffrage from the age of 18 regardless of race, sex, or wealth. There are some limits, however: felons are disenfranchised and in some states former felons are likewise. Furthermore, the national representation of territories and the federal district of Washington, DC in Congress is limited: residents of the District of Columbia are subject to federal laws and federal taxes but their only Congressional representative is a non-voting delegate.

Federal government

The federal government is the national government, comprising the Legislative Branch (led by Congress), the Executive Branch (led by the President), and the Judicial Branch (led by the Supreme Court). These three branches were designed to apply checks and balances on each other. The Constitution limits the powers of the federal government to defense, foreign affairs, the issuing and management of currency, the management of trade and relations between the states, and the protection of human rights. In addition to these explicitly stated powers, the federal government—with the assistance of the Supreme Court—has gradually extended these powers into such areas as welfare and education, on the basis of the "necessary and proper" clause of the Constitution.

The Congress

necessary and proper The Congress of the United States is the legislative branch of the federal government of the United States. It is bicameral, comprising the House of Representatives and the Senate. The House of Representatives consists of 435 members, each of whom represents a congressional district and serves for a two-year term. House seats are apportioned among the states by population; in contrast, each state has two Senators, regardless of population. There are a total of 100 senators, who serve six-year terms. The powers of Congress are limited to those enumerated in the Constitution; all other powers are reserved to the states and the people. The Constitution also includes the necessary-and-proper clause, which grants Congress the power to "make all laws which shall be necessary and proper for carrying into execution the foregoing powers."

The President

necessary-and-proper clause At the top level of the executive branch is the President of the United States. The President and Vice-President are elected as 'running mates' for four-year terms by the Electoral College, for which each state, as well as the District of Columbia, is allocated a number of seats based on its representation (or ostensible representation, in the case of D. C.) in both houses of Congress (see U.S. Electoral College). The relationship between the President and the Congress reflects that between the English monarchy and parliament at the time of the framing of the United States Constitution. Congress can legislate to constrain the President's executive power, even with respect to his or her command of the armed forces; however, this power is used only very rarely—a notable example was the constraint placed on President Richard Nixon's strategy of bombing Cambodia during the Vietnam War. The President cannot directly propose legislation, and must rely on supporters in Congress to promote his or her legislative agenda. The President's signature is required to turn congressional bills into law; in this respect, the President has the power—only occasionally used—to veto congressional legislation. Congress can override a presidential veto with a two-thirds majority vote in both houses. The ultimate power of Congress over the President is that of impeachment or removal of the elected President through a House vote, a Senate trial, and a Senate vote. The threat of using this power has had major political ramifications in the cases of Presidents Andrew Johnson, Richard Nixon, and Bill Clinton. The President makes around 2,000 executive appointments, including members of the Cabinet and ambassadors, which must be approved by the Senate; the President can also issue executive orders and pardons, and has other Constitutional duties, among them the requirement to give a State of the Union address to Congress once a year. Although the President's constitutional role may appear to be constrained, in practice, the office carries enormous prestige that typically eclipses the power of Congress: the Presidency has justifiably been referred to as 'the most powerful office in the world'. The Vice President is first in the line of succession, and is the President of the Senate ex officio, with the ability to cast a tie-breaking vote. The members of the President's Cabinet are responsible for administering the various departments of state, including the Department of Defense, the Justice Department, and the State Department. These departments and department heads have considerable regulatory and political power, and it is they who are responsible for executing federal laws and regulations. George W. Bush is the 43rd President, currently serving his second term.

The Courts

George W. Bush The highest court is the Supreme Court, which consists of nine justices. The court deals with federal and constitutional matters, and can declare legislation made at any level of the government as unconstitutional, nullifying the law and creating precedent for future law and decisions. Below the Supreme Court are the courts of appeals, and below them in turn are the district courts, which are the general trial courts for federal law. Separate from, but not entirely independent of, this federal court system are the individual court systems of each state, each dealing with its own laws and having its own judicial rules and procedures. A case may be appealed from a state court to a federal court only if there is a federal question; the supreme court of each state is the final authority on the interpretation of that state's laws and constitution.

State and local governments

supreme court of each state. Note that Alaska and Hawaii are shown at different scales, and that the Aleutian Islands and the uninhabited Northwestern Hawaiian Islands are omitted from this map.]] The state governments have the greatest influence over people's daily lives. Each state has its own written constitution and has different laws. There are sometimes great differences in law and procedure between the different states, concerning issues such as property, crime, health, and education. The highest elected official of each state is the Governor. Each state also has an elected legislature (bicameral in every state except Nebraska), whose members represent the different parts of the state. Of note is the New Hampshire legislature, which is the third-largest legislative body in the English-speaking world, and has one representative for every 3,000 people. Each state maintains its own judiciary, with the lowest level typically being county courts, and culminating in each state supreme court, though sometimes named differently. In some states, supreme and lower court justices are elected by the people; in others, they are appointed, as they are in the federal system. The institutions that are responsible for local government are typically town, city, or county boards, making laws that affect their particular area. These laws concern issues such as traffic, the sale of alcohol, and keeping animals. The highest elected official of a town or city is usually the mayor. In New England, towns operate directly democratically, and in some states, such as Rhode Island and Connecticut, counties have little or no power, existing only as geographic distinctions. In other areas, county governments have more power, such as to collect taxes and maintain law enforcement agencies.

Political divisions

With the Declaration of Independence, the thirteen colonies proclaimed themselves to be nation states modeled after the European states of the time. Although considered as sovereigns initially, under the Articles of Confederation of 1781 they entered into a "Perpetual Union" and created a fully sovereign federal state, delegating certain powers to the national Congress, including the right to engage in diplomatic relations and to levy war, while each retaining their individual sovereignty, freedom and independence. But the national government proved too ineffective, so the administrative structure of the government was vastly reorganized with the United States Constitution of 1789. Under this new union, the continued status of the individual states as sovereign nation states fell into dispute in 1861, as several states attempted to secede from the union; in response, then-President Abraham Lincoln claimed that such secession was illegal, and the result was the American Civil War. Since the Union victory in 1865, the independent status of the individual states has not been broached again by any state, and the status of each state within the union has been deemed by mainstream officials and academics to be settled as being subordinate to the union as a whole. In subsequent years, the number of states grew steadily due to western expansion, the purchase of lands by the national government from other nation states, and the subdivision of existing states, resulting in the current total of 50. The states are generally divided into smaller administrative regions, including counties, cities and townships. The United States–Canadian border is the longest undefended political boundary in the world. The U.S. is divided into three distinct sections:
- the "continental United States," also known as "the Lower 48" and more accurately termed the conterminous, coterminous or contiguous United States
- Alaska, which is physically connected only to Canada
- the archipelago of Hawaii, in the central Pacific Ocean. The United States also holds several other territories, districts, and possessions, notably the federal district of the District of Columbia, which is the nation's capital, and several overseas insular areas, the most significant of which are American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands. The Palmyra Atoll is the United States' only incorporated territory; it is unorganized and uninhabited. The United States Navy has held a base at a portion of Guantanamo Bay, Cuba, since 1898. The United States government possesses a lease to this land, which only mutual agreement or United States abandonment of the area can terminate. The present Cuban government of Fidel Castro disputes this arrangement, claiming Cuba was not truly sovereign at the time of the signing. The United States argues this point moot because Cuba apparently ratified the lease post-revolution, and with full sovereignty, when it cashed one rent check in accordance with the disputed treaty.

Foreign relations and military