Terns are seabirds in the family Sternidae, previously considered a subfamily (Sterninae) of the gull family Laridae (van Tuinen et al., 2004). They form a lineage with the gulls and skimmers which in turn is related to skuas and auks. Terns have a worldwide distribution.
Most terns were formerly treated as belonging into one large genus Sterna, with the other genera being small, but analysis of DNA sequences supports the splitting of Sterna into several smaller genera (see list, below) (del Hoyo et al., 1996; Bridge et al. 2005; Collinson 2006).
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 Great Britain in summer 1982, reached Melbourne, Australia in October 1982, a sea journey of over 22,000 km (14,000 statute 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.
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.
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. Terns ranges in size from the Least Tern, at 42 g (1.5 oz) and 23 cm (9 inches), to the Caspian Tern, at 630 g (1.4 lbs) and 53 cm (21 inches).
Sternidae Bonaparte, 1838
The White Tern (Gygis alba) is a small seabird found across the tropical oceans of the world. Sometimes known as the Fairy Tern (but not the Fairy Tern, Sternula nereis), this small tern is famous for laying its egg on bare thin branches in a small fork or depression without a nest. This balancing act is a predator-avoidance behavior as the branches they choose are too small for rats or even small lizards to climb. Safe from predators, but still vulnerable to strong winds, the White Terns are also quick to relay should they lose the egg. The newly hatched chicks have well developed feet to hang on to their precarious nesting site with. It is a long-lived bird, having been recorded living for 17 years.
The White Tern is a small, all white tern with a long black bill, related to the noddies. It ranges widely across the Pacific and Indian Oceans, and also nests in some Atlantic islands. It nests on coral islands, usually on trees with thin branches but also on rocky ledges and on man-made structures. The White Tern feeds on small fish which it catches by plunge diving.
The White Tern is not considered threatened as it is a wide-spread species with several large colonies around the world.
The Grey-backed Tern, Onychoprion lunatus, is a seabird in the tern family. A close relative of the Bridled and Sooty Terns (with which it is sometimes confused), the Grey-backed Tern is less common than the other members of its genus and is has been studied less. The three species, along with the Aleutian Tern were recently split into a new genus Onychoprion from Sterna (Bridge et al., 2005). They resemble the Sooty Tern but with a grey back instead of a black one. Their breast and under parts are white, and the have a black eye line from the bill to the back of the head which gives them their other name, the Spectacled Tern.
The Grey-backed Tern breeds on islands of the tropical Pacific Ocean. At the northern end of its distribution it nests in the Northwestern Hawaiian Islands (with the largest population being Lisianski Island) and two small islets off Oahu, in the east as far as the Tuamotu Islands, with other colonies in the Society Islands, the Line Islands, Phoenix Islands, Mariana Islands and American Samoa. There are unconfirmed reports of breeding as far south as Fiji, and as far east as Easter Island. Little is known about the populations outside of Hawaii. Outside of the breeding season the species is partly migratory, with birds from the Hawaiian Islands flying south. It is thought that birds in other parts of the Pacific are also migratory, and will disperse as far as Papua New Guinea, the Philippines, and Easter Island.
The Arctic Tern (Sterna paradisaea) is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding colonially in Arctic and sub-Arctic regions of Europe, Asia, and North America (as far south as Brittany and Massachusetts). The species is strongly migratory, seeing two summers each year as it migrates from its northern breeding grounds to the oceans around Antarctica and back (about 24,000 miles) each year. This is the longest regular migration by any known animal.
Arctic Terns are medium-sized birds. They have a length of 33-39 centimeters (13-15 in) and a wingspan of 76-85 cm (26-30 in). They are mainly grey and white plumaged, with a red beak (as long as the head, straight, with pronounced gonys) and feet, white forehead, a black nape and crown (streaked white), and white cheeks. The grey mantle is 305 mm, and the scapulars are fringed brown, some tipped white. The upper wing is grey with a white leading edge, and the collar is completely white, as is the rump. The deeply forked tail is whitish, with grey outer webs. The hindcrown to the ear-coverts is black.
Arctic Terns are long-lived birds, with many reaching twenty years of age. They eat mainly fish and small marine invertebrates. The species is abundant, with an estimated one million individuals. While the trend in the number of individuals in the species as a whole is not known, exploitation in the past has reduced this bird's numbers in the southern reaches of its range.
The Arctic Tern has a worldwide, circumpolar breeding distribution which is continuous; there are no recognized subspecies. It can be found in coastal regions in cooler temperate parts of North America and Eurasia during the northern summer. While wintering during the southern summer, it can be found at sea, reaching the southern edge of the Antarctic ice. The species' range encompasses an area of approximately ten million square kilometers.
The Arctic Tern is famous for its migration; it flies from its Arctic breeding grounds to the Antarctic and back again each year. This 19,000 km (12,000 mi) journey each way ensures that this bird sees two summers per year and more daylight than any other creature on the planet. The average Arctic Tern in its life will travel a distance equal to going to the moon and back—about 500,000 miles. One example of this bird's remarkable long-distance flying abilities involves an Arctic Tern ringed as an unfledged chick on the Farne Islands, Northumberland, UK in summer 1982, which reached Melbourne, Australia in October 1982, a sea journey of over 22,000 km (14,000 mi) in just three months from fledging. Another example is that of a chick ringed in Labrador, Canada on 23 July 1928. It was found in South Africa four months later.
The Arctic Tern is medium-sized bird approximately 33-36 cm (13-15 in) from the tip of its beak to the tip of its tail. The wingspan is 76-85 cm. The weight is 86-127 g (3.0-4.5 oz). The beak is dark red, as are the short legs and webbed feet. Like most terns, the Arctic Tern has high aspect ratio wings and a tail with a deep fork.
The Least Tern (Sternula antillarum, formerly Sterna antillarum) is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the Little Tern S. albifrons of the Old World. Other close relatives include the Yellow-billed Tern S. superciliaris and Peruvian Tern S. lorata, both from South America.
It is a small tern, 22-24 cm long, with a wingspan of 50 cm, and weighing 39-52 g. The upper parts are a fairly uniform pale gray, and the under parts white. The head is white, with a black cap and line through the eye to the base of the bill, and a small white forehead patch above the bill; in winter, the white forehead is more extensive, with a smaller and less sharply defined black cap. The bill is yellow with a small black tip in summer, all blackish in winter. The legs are yellowish. The wings are mostly pale gray, but with conspicuous black markings on their outermost primaries. In behavior, it flies over water with fast, jerky wingbeats and a distinctive hunchback appearance, with the bill pointing slightly downward.
It is migratory, wintering in Central America, the Caribbean and northern South America. It has occurred as a vagrant to Europe, with one record in Great Britain.
It differs from Little Tern mainly in that its rump and tail are gray, not white, and it has a different, more squeaking call; from Yellow-billed Tern in being paler gray above and the bill having a short (not no) black tip; and from Peruvian Tern in being paler gray above and white (not pale gray) below and a shorter black tip to the bill.
The Large-billed Tern (Phaetusa simplex) is a species of tern in the Sternidae family.
It is found in Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Trinidad and Tobago, Uruguay, and Venezuela. It has occurred as a vagrant in Aruba, Bermuda, Cuba, Panama and the United States. Its natural habitats are rivers and freshwater lakes.
The Caspian Tern (Hydroprogne caspia, formerly Sterna caspia; syn. Hydroprogne tschegrava) is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic, with no subspecies accepted. In New Zealand it is also known by the Maori name Taranui.
It is the world's largest tern, 48-56 cm long, with a wingspan of 127-140 cm and a weight of 574-782g. Adult birds have black legs, and a long thick red-orange bill with a small black tip. They have a white head with a black cap and white neck, belly and tail. The upper wings and back are pale grey; the under wings are pale with dark primary feathers. In flight, the tail is less forked than other terns and wing tips black on the underside. In winter, the black cap is still present (unlike many other terns), but with some white streaking on the forehead. The call is a loud heron-like croak.
Their breeding habitat is large lakes and ocean coasts in North America (including the Great Lakes), and locally in Europe (mainly around the Baltic Sea and Black Sea), Asia, Africa, and Australasia (Australia and New Zealand). North American birds migrate to southern coasts, the West Indies and northernmost South America. European and Asian birds winter in the Old World tropics. African and Australasian birds are resident or disperse over short distances.
The Gull-billed Tern, Gelochelidon nilotica, formerly Sterna nilotica (Bridge et al., 2005), is a seabird of the tern family Sternidae.
It breeds in warmer parts of the world in southern Europe (and a very small isolated population in northern Germany and Denmark), temperate and eastern Asia, both coasts of North America, eastern South America and Australia. This bird has a number of geographical races, differing mainly in size and minor plumage details.
All forms show a post-breeding dispersal, but the northern breeders are most migratory, wintering south to Africa, the Caribbean and northern South America, southern Asia and New Zealand.
This species breeds in colonies on lakes, marshes and coasts. It nests in a ground scrape and lays two to five eggs.
The Gull-billed Tern does not normally plunge dive for fish like the other white terns, but feeds on insects taken in flight, and also often hunts over wet fields, to take frogs and small mammals (mice, voles, etc).
This is a fairly large and powerful tern, similar in size and general appearance to a Sandwich Tern, but the short thick gull-like bill, broad wings, long legs and robust body are distinctive. The summer adult has grey upperparts, white under parts, a black cap, strong black bill and black legs. The call is a characteristic ker-wik.
The Royal Tern (Thalasseus maximus, syn. Sterna maxima - see Bridge et al., 2005) is a seabird in the tern family Sternidae. This bird has two distinctive subspecies.
T. m. maximus breeds on the Atlantic and Pacific coasts of the southern USA and Mexico into the Caribbean. The slightly smaller T. m. albididorsalis breeds in coastal west Africa.
American birds winter south to Peru and Argentina, and African breeders move both north and south from the breeding colonies.
African birds may reach as far north as Spain. This species has also wandered to western Europe as a rare vagrant, these records probably being from the American colonies.
This is a large tern, second only to Caspian Tern but is unlikely to be confused with that carrot-billed giant, which has extensive dark underwing patches. Royal Tern has a long yellow bill, pale grey upperparts and white underparts. Its legs are black. In winter, the black cap becomes patchy. Juvenile Royal Terns have a scaly-backed appearance. The call is a characteristic loud grating noise like a Sandwich Tern.
The Inca Tern, Larosterna inca, is a seabird in the family Sternidae. It is the only member of the genus Larosterna.
This uniquely-plumaged bird breeds on the coasts of Peru and Chile, and is restricted to the Humboldt current. It can be identified by its dark grey body, white moustache on the both sides of its head, and red-orange beak and feet.
The Inca Tern breeds on rocky cliffs. It nests in a hollow or burrow or sometimes the old nest of a Humboldt Penguin, and lays one or two eggs. The eggs are incubated for about 4 weeks, and the chicks leave the nest after 7 weeks.
This is a large tern, 41cm long. Sexes are similar; the adult is mostly slate-grey with white restricted to the facial plumes and the trailing edges of the wings. The large bill and legs are dark red. Immature birds are purple-brown, and gradually develop the facial plumes.
The Inca Tern feeds by plunge diving for fish like a Sterna tern. Its call is a cat-like mew.
The Black Tern, Chlidonias niger, is a small tern generally found in or near inland water in Europe and North America. As its name suggests, it has predominantly dark plumage.
Adult are 25 cm (9.75 in) long, with a wing span 61 cm (24 in), and weigh 62 g (2.2 oz). They have short dark legs and a short, weak-looking black bill, measuring 27-28 mm, nearly as long as the head. The bill is long, slender, and looks slightly decurved. They have a dark grey back, with a white forehead, black head, neck (occasionally suffused with gray in the adult) and belly, black or blackish-brown cap (which unites in color with the ear coverts, forming an almost complete hood), and a light brownish-grey, 'square' tail. The face is white. There is a big dark triangular patch in front of the eye, and a broadish white collar in juveniles. There are grayish-brown smudges on the ides of the white breast, a downwards extension of the plumage of the upperparts. These marks vary in size and are not conspicuous. In non-breeding plumage, most of the black, apart from the cap, is replaced by grey. The plumage of the upperparts is drab, with pale feather-edgings. The rump is brownish-gray. The North American race, C. n. surinamensis, is distinguishable from the European form in all plumages, and is considered by some to be a separate species.
In flight, the build appears slim. The wing-beats are full and dynamic.
Classification and species list
A recent study (Thomas et al., 2004) of part of the cyt b gene sequence found a closer relationship between terns and the Thinocori, some species of aberrant waders. These results are in disagreement with other molecular and morphological studies (see Paton & Baker, 2006) and are best interpreted to prove an extraordinary amount of molecular convergent evolution between the terns and these waders, or as retention of an ancient genotype.
According the mtDNA studies and review by Bridge et al (2005), the genera and species of terns are as follows:
- Genera 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
- Little White Tern Gygis microrhyncha
- Genus Onychoprion - "brown-backed" terns
- Grey-backed Tern Onychoprion lunata
- Bridled Tern Onychoprion anaethetus
- Sooty Tern Onychoprion fuscata
- Aleutian Tern Onychoprion aleutica
- Genus Sternula - little white terns
- Fairy Tern Sternula nereis
- Damara Tern Sternula balaenarum
- Little Tern Sternula albifrons
- Saunders's Tern Sternula saundersi (formerly considered a subspecies of Little Tern)
- Least Tern Sternula antillarum (formerly considered a subspecies of Little Tern)
- Yellow-billed Tern Sternula superciliaris
- Peruvian Tern Sternula lorata
- Genus Phaetusa - Large-billed Tern
- Large-billed Tern Phaetusa simplex
- Genus Hydroprogne - Caspian Tern
- Caspian Tern Hydroprogne caspia
- Genus Gelochelidon - Gull-billed Tern
- Gull-billed Tern Gelochelidon nilotica
- Genus Larosterna - Inca Tern
- Inca Tern Larosterna inca
- Genus Chlidonias - marsh terns
- Black Tern Chlidonias niger
- White-winged Tern or White-winged Black Tern Chlidonias leucopterus
- Whiskered Tern Chlidonias hybridus
- Black-fronted Tern Chlidonias albostriatus (ex-Sterna albostriata)
- Genus Thalasseus - crested terns
- Lesser Crested Tern Thalasseus bengalensis
- Royal Tern Thalasseus maximus
- Greater Crested Tern or Swift Tern, Thalasseus bergii
- Chinese Crested Tern Thalasseus bernsteini
- Elegant Tern Thalasseus elegans
- Sandwich Tern Thalasseus sandvicensis
- Genus Sterna - large white terns
- Forster's Tern Sterna forsteri
- Trudeau's Tern Sterna trudeaui
- Common Tern Sterna hirundo
- Roseate Tern Sterna dougallii
- White-fronted Tern Sterna striata
- Black-naped Tern Sterna sumatrana
- South American Tern Sterna hirundinacea
- Antarctic Tern Sterna vittata
- Kerguelen Tern Sterna virgata
- Arctic Tern Sterna paradisaea
- River Tern Sterna aurantia
- Black-bellied Tern Sterna acuticauda (possibly Chlidonias)
- White-cheeked Tern Sterna repressa (possibly Chlidonias)