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Range Description

This species can be found found on islands and coastlines of the tropical and subtropical Old World, ranging from the Atlantic Coast of South Africa, south around the Cape and continuing along the coast of Africa and Asia almost without break to south-east Asia and Australia. It can also be found on Madagascar, islands of the western Indian ocean and islands of the western and central Pacific Ocean. Outside the breeding season it can be found at sea throughout this range, with the exception of the central Indian Ocean (del Hoyo et al. 1996).
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Physical Description

Diagnostic Description


Length: 46-50 cm. Plumage: above, dark grey tail, rump, wings and back with white leading and trailing edges to spread wing; white collar on hindneck; crest and crown black; clearly demarcated forehead white (white speckling on forecrown in non-breeding bird); underparts white. Immature above dark brownish black with white edges to feathers. Bare parts: iris dark brown; bill yellow or geenish yellow; feet and legs black sometimes with yellow soles. Habitat: seashores and estuaries. Breeds in WIO. <389><391><393>
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Source: World Register of Marine Species


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Habitat and Ecology

Habitat and Ecology
Behaviour Many populations of this species remain sedentary in their breeding areas or disperse locally (del Hoyo et al. 1996) although some are more migratory (Urban et al. 1986). The species breeds in large dense colonies, or in small groups of less than 10 pairs amidst colonies of other species (e.g. King Gull Larus hartlaubii or Silver Gull Larus novaehollandiae) (del Hoyo et al. 1996). It usually forages singly (Urban et al. 1986) or in small groups (del Hoyo et al. 1996) but several hundred individuals may gather at roost sites (Langrand 1990). Habitat The species inhabits tropical and subtropical coastlines, foraging in the shallow waters of lagoons (Higgins and Davies 1996, del Hoyo et al. 1996), coral reefs (del Hoyo et al. 1996), estuaries (Urban et al. 1986, del Hoyo et al. 1996), bays, harbours and inlets (Higgins and Davies 1996), along sandy, rocky, coral (del Hoyo et al. 1996) or muddy shores, on rocky outcrops in open sea, in mangrove swamps (Langrand 1990) and also far out to sea on open water (del Hoyo et al. 1996). It shows a preference for nesting on offshore islands (Urban et al. 1986, del Hoyo et al. 1996), low-lying coral reefs, sandy or rocky coastal islets, coastal spits, lagoon mudflats (del Hoyo et al. 1996), and artificial islets in saltpans and sewage works (Urban et al. 1986, del Hoyo et al. 1996) within 3 km of the coast (del Hoyo et al. 1996). Diet Its diet consists predominantly of pelagic fish 10-50 cm long (Urban et al. 1986, del Hoyo et al. 1996) although it will also take cephalopods (e.g. squid), crustaceans (del Hoyo et al. 1996) (e.g. crabs (del Hoyo et al. 1996) and prawns (Higgins and Davies 1996)), insects and hatchling turtles opportunistically (del Hoyo et al. 1996). Breeding site The nest is a shallow scrape in bare sand, rock or coral (del Hoyo et al. 1996) in flat open sites (Urban et al. 1986) on offshore islands (Urban et al. 1986, del Hoyo et al. 1996), low-lying coral reefs, sandy or rocky coastal islets, coastal spits, lagoon mudflats (del Hoyo et al. 1996) or islets in saltpans and sewage works (Urban et al. 1986, del Hoyo et al. 1996). The species nests in dense colonies (Urban et al. 1986) with neighbouring nests very close together (rims may be touching) (del Hoyo et al. 1996), and usually forages within 3 km of the breeding colony (del Hoyo et al. 1996).

  • Terrestrial
  • Marine
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Depth range based on 30 specimens in 2 taxa.
Water temperature and chemistry ranges based on 30 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 27.353 - 27.501
  Nitrate (umol/L): 0.038 - 0.050
  Salinity (PPS): 34.912 - 34.984
  Oxygen (ml/l): 4.655 - 4.664
  Phosphate (umol/l): 0.160 - 0.169
  Silicate (umol/l): 3.208 - 3.344

Graphical representation

Temperature range (°C): 27.353 - 27.501

Nitrate (umol/L): 0.038 - 0.050

Salinity (PPS): 34.912 - 34.984

Oxygen (ml/l): 4.655 - 4.664

Phosphate (umol/l): 0.160 - 0.169

Silicate (umol/l): 3.208 - 3.344
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.


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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Thalasseus bergii

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 4
Species With Barcodes: 1
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Source: Barcode of Life Data Systems (BOLD)


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Conservation Status

IUCN Red List Assessment

Red List Category
Least Concern

Red List Criteria


Year Assessed

BirdLife International

Butchart, S. & Symes, A.


This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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Status in Egypt

Migrant breeder and winter visitor.

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Source: Bibliotheca Alexandrina - EOL Ar


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The global population is estimated to number c.150,000-1,100,000 individuals (Wetlands International 2006), while national population estimates include: c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in China; c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Taiwan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan (Brazil 2009).

Population Trend
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Major Threats
The species is vulnerable to human disturbance (e.g. tourism) at breeding colonies on offshore islands (Benoit and Bretagnolle 2002) which can lead to nest desertion and increased predation of eggs and nestlings by gulls and ibises (Cooper et al. 1990). The species is also threatened by injury and mortality from entanglement with baited hooks, fishing lines, nets and human refuse (e.g. plastic bags) (Cooper et al. 1990). Utilisation Most breeding colonies of this species are subject to subsistence egg collecting (de Korte 1991, del Hoyo et al. 1996).
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Greater crested tern

The greater crested tern[3] (Thalasseus bergii), also called crested tern or swift tern, is a seabird in the tern family that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World. Its five subspecies breed in the area from South Africa around the Indian Ocean to the central Pacific and Australia, all populations dispersing widely from the breeding range after nesting. This large tern is closely related to the royal and lesser crested terns, but can be distinguished by its size and bill colour.

The greater crested tern has grey upperparts, white underparts, a yellow bill, and a shaggy black crest that recedes in winter. Its young have a distinctive appearance, with strongly patterned grey, brown and white plumage, and rely on their parents for food for several months after they have fledged. Like all members of the genus Thalasseus, the greater crested tern feeds by plunge diving for fish, usually in marine environments; the male offers fish to the female as part of the courtship ritual.

This is an adaptable species that has learned to follow fishing boats for jettisoned bycatch, and to use unusual nest sites such as the roofs of buildings and artificial islands in salt pans and sewage works. Its eggs and young are taken by gulls and ibises, and human activities such as fishing, shooting and egg harvesting have caused local population declines. There are no global conservation concerns for this bird, which has a stable total population of more than 500,000 individuals.


The terns, family Sternidae, are small to medium-sized seabirds closely related to the gulls, skimmers and skuas. They are gull-like in appearance, but typically have a lighter build, long pointed wings (which give them a fast, buoyant flight), a deeply forked tail and short legs. Most species are grey above and white below, and have a black cap that is reduced or flecked with white in the winter.[4]


T. bengalensis

T. maxima



T. sandvicensis

T. elegans

Relationships in the genus Thalasseus[5]

The greater crested tern was originally described as Sterna bergii by German naturalist Martin Lichtenstein in 1823, but was moved to its current genus, Thalasseus,[6] after mitochondrial DNA studies confirmed that the three main head patterns shown by terns (no black cap, black cap, black cap with a white forehead) corresponded to distinct clades.[7]

The greater crested tern's closest relatives within its genus appear to be the lesser crested tern (T. bengalensis), and the royal tern (T. maximus).[7] The DNA study did not include the critically endangered Chinese crested tern (T. bernsteini) but, as that bird was formerly considered to be conspecific with the greater crested tern as a synonym of the subspecies T. b. cristatus, it is presumably also very closely related.[8]

The generic name of the greater crested tern is derived from Greek Thalassa, "sea", and the species epithet bergii commemorates Carl Heinrich Bergius, a Prussian pharmacist and botanist who collected the first specimens of this tern near Cape Town.[9]

The greater crested tern has about five geographical races, differing mainly in the colour of the upperparts and bill. These are listed below in taxonomic sequence. A similar number of other potential subspecies have been proposed, but are not considered valid.[10]

Subspecies[11]Breeding rangeDistinctive featuresPopulation estimates
T. b. bergii[12]
(Lichtenstein, 1823)
Coasts of South Africa and NamibiaDark grey above, slightly larger than thalassina, least white on head[13]20,000 individuals (inc 6,336 breeding pairs in South Africa and up to 1,682 pairs in Namibia)[14]
T. b. enigma[12][15]
(Clancey, 1979)
Zambezi delta, Mozambique, south to Durban, South AfricaPalest subspecies[10]8,000–10,000 individuals in Madagascar and Mozambique[14]
T. b. cristata[13]
(Stephens, 1826)
Eastern Indian Ocean, Australia and western Pacific OceanLike bergii, with tail, rump and back concolorous. paler in Australia500,000+ individuals in Australia[10]
T. b. thalassina[13]
(Stresemann, 1914)
Western Indian OceanSmall and pale, larger and less pale in south of range2,550–4,500 individuals in Eastern Africa and Seychelles[14]
T. b. velox[13]
(Cretzschmar, 1827)
Red Sea, Persian Gulf, northern Indian OceanLargest, heaviest, darkest and longest-billed subspecies33,000 in Middle East (inc 4,000 pairs Oman and 3,500 pairs on islands off Saudi Arabia)[10]


Non-breeding adult T. b. cristata

The greater crested tern is a large tern with a long (5.4–6.5 cm, 2.1–2.6 in) yellow bill, black legs, and a glossy black crest that is noticeably shaggy at its rear. The breeding adult of the nominate subspecies T. b. bergii is 46–49 cm (18–19 in) long, with a 125–130 cm (49–51 in) wing-span; this subspecies weighs 325–397 g (11.4–14.0 oz).[13] The forehead and the underparts are white, the back and inner wings are dusky-grey. In winter, the upperparts plumage wears to a paler grey, and the crown of the head becomes white, merging at the rear into a peppered black crest and mask.[16]

The adults of both sexes are identical in appearance, but juvenile birds are distinctive, with a head pattern like the winter adult, and upperparts strongly patterned in grey, brown, and white; the closed wings appear to have dark bars. After moulting, the young terns resemble the adult, but still have a variegated wing pattern with a dark bar on the inner flight feathers.[13]

First year T. b. cristata

The northern subspecies T. b. velox and T. b. thalassina are in breeding plumage from May to September or October, whereas the relevant period for the two southern African races is from December to April. For T. b. cristata, the moult timing depends on location; birds from Australia and Oceania are in breeding plumage from September to about April, but those in Thailand, China and Sulawesi have this appearance from February to June or July.[13]

The royal tern is similar in size to this species, but has a heavier build, broader wings, a paler back and a blunter, more orange bill. The greater crested often associates with the lesser crested tern, but is 25% larger than the latter, with a proportionately longer bill, longer and heavier head, and bulkier body.[16] Lesser crested tern has an orange-tinted bill, and in immature plumage it is much less variegated than greater crested.[12]

The greater crested tern is highly vocal, especially at its breeding grounds. The territorial advertising call is a loud, raucous, crow-like kerrak. Other calls include a korrkorrkorr given at the nest by anxious or excited birds, and a hard wep wep in flight.[16]

Distribution and habitat[edit]

Roosting with little terns, note size difference

The greater crested tern occurs in tropical and warm temperate coastal parts of the Old World from South Africa around the Indian Ocean to the Pacific and Australia. The subspecies T. b. bergii and T. b. enigma breed in Southern Africa from Namibia to Tanzania, and possibly on islands around Madagascar. There is then a break in the breeding distribution of this species until Somalia and the Red Sea, and another discontinuity further east in southern India.[10]

The greater crested tern breeds on many islands in the Indian Ocean including Aldabra and Etoile in the Seychelles, the Chagos Archipelago, and Rodrigues.[17] There are colonies on numerous Pacific islands, including Kiribati, Fiji, Tonga, the Society Islands and the Tuamotus.[18]

The nests are located on low‑lying sandy, rocky, or coral islands, sometimes amongst stunted shrubs, often without any shelter at all.[16] When not breeding, the greater crested tern will roost or rest on open shores, less often on boats, pilings, harbour buildings and raised salt mounds in lagoons. It is rarely seen on tidal creeks or inland waters.[14]

In flight

All populations of greater crested tern disperse after breeding. When Southern African birds leave colonies in Namibia and Western Cape Province, most adults move east to the Indian Ocean coastline of South Africa. Many young birds also travel east, sometimes more than 2,000 km (1,200 mi), but others move northwards along the western coast. T. b. thalassina winters on the east African coast north to Kenya and Somalia and may move as far south as Durban. Populations of T. b. velox breeding from the Persian Gulf eastwards appear to be sedentary or dispersive rather than truly migratory, but those breeding in the Red Sea winter south along the east African coast to Kenya.[14] T. b. cristata mostly stays within 400 km (260 mi) of its colonies, but some birds wander up to around 1,000 km (600 mi).[19] This species has occurred as a vagrant to Hawaii,[20] New Zealand,[21][22] North Korea,[21] Jordan,[21] and Israel.[16]



T. b. cristata displaying

The greater crested tern breeds in colonies, often in association with other seabirds. It is monogamous and the pair bond is maintained through the year and sometimes in consecutive breeding seasons.[23] The colony size is related to the abundance of pelagic fish prey,[14] and the largest documented colony, with 13,000 to 15,000 pairs, is in the Gulf of Carpentaria in northern Australia, a region which also supports major colonies of other seabirds. Since nesting in this area follows the summer monsoonal flooding, it is presumably a response to fish stocks rising, probably due to river run-off providing extra nutrient to the Gulf.[24] This tern does not show site fidelity, frequently changing its nest site from year to year,[16] sometimes by more than 200 km (130 mi).[19]

Tropical sandy islands are used for breeding and roosting, but may be disturbed by human activities.

A male greater crested tern establishes a small area of the colony in preparation for nesting, and initially pecks at any other tern entering his territory. If the intruder is another male, it retaliates in kind, and is normally vigorously repelled by the incumbent. A female entering the nest area reacts passively to the male's aggression, enabling him to recognise her sex and initiate pair formation by display, including head raising and bowing; this behaviour is frequently repeated during nesting to reinforce the bond between the pair. Terns also use fish as part of the courtship ritual. One bird flies around the colony with a fish in its beak, calling loudly; its partner may also fly, but the pair eventually settle and the gift is exchanged.[25]

Breeding plumage in New South Wales

The nest is a shallow scrape in the sand on open, flat or occasionally sloping ground. It is often unlined, but sometimes includes stones or cuttlefish bones. One, sometimes two, eggs are laid and incubated by both parents for 25 to 30 days prior to hatching.[14] The eggs are cream with blackish streaks.[26] Egg laying is synchronised within a breeding colony[27] and more tightly so within sub-colonies.[28] Parents do not recognize their own eggs or newly hatched chicks, but are able to distinguish their chicks by the time they are two days-old, shortly before they begin to wander from the nest.[29] The precocial chicks, which are very pale with black speckling, are brooded and fed by both parents, but may gather in crèches when older. The young terns fledge after 38 to 40 days, but remain dependent on the parents after leaving the colony until they are about four months old.[14]

A nesting colony in Tubbataha Reef, Philippines
Egg, Collection Museum Wiesbaden

In South Africa, this species has adapted to breeding on the roofs of building, sometimes with Hartlaub's gull, which also shares the more typical nesting sites of the nominate race. In 2000, 7.5% of the population of this subspecies bred on roofs.[30] Artificial islands in salt pans and sewage works have also recently been colonised by this adaptable seabird.[10]

Adult terns have few predators, but in Namibia immature birds are often robbed of their food by kelp gulls, and that species, along with Hartlaub's gull, silver gull and sacred ibis, has been observed feeding on eggs or nestlings, especially when colonies are disturbed.[10][31] Smaller subcolonies with a relatively larger numbers of nests located on the perimeter are subject to more predation.[28] In Australia, predation by cats and dogs, and occasional deaths by shooting or collisions with cars, wires or light-towers have been documented.[9]

Nominate subspecies roosting with Sandwich terns in South Africa

Commercial fisheries can have both positive and negative effects on the greater crested tern. Juvenile survival rates are improved where trawler discards provide extra food, and huge population increases in the southeastern Gulf of Carpentaria are thought to have been due to the development of a large prawn trawl fishery.[32] Conversely, purse-seine fishing reduces the available food supply, and sizeable fluctuations in the numbers of great crested terns breeding in the Western Cape of South Africa are significantly related to changes in the abundance of pelagic fish, which are intensively exploited by purse-seine fishing.[31] Terns may be killed or injured by collisions with trawl warps, trapped in trawls or discarded gear, or hooked by longline fishing, but, unlike albatrosses and petrels, there is little evidence that overall numbers are significantly affected.[14]

An unusual incident was the incapacitation of 103 terns off Robben Island, South Africa by marine foam, generated by a combination of wave action, kelp mucilage and phytoplankton. After treatment, 90% of the birds were fit to be released.[33]


Sardines are a common food item.

Fish are the main food of the greater crested tern, found to make up nearly 90% of all prey items with the remainder including cephalopods, crustaceans and insects.[14] Unusual vertebrate prey included agamid lizards and green turtle hatchlings.[32]

The great crested tern feeds mostly at sea by plunge diving to a depth of up to 1 m (3 ft), or by dipping from the surface, and food is usually swallowed in mid-air. Birds may forage up to 10 km (6 mi) from land in the breeding season. Prey size ranges from 7–138 mm (0.27–5.4 in) in length and up to 30 g (1.1 oz) in weight. Shoaling pelagic fish such as anchovy and sardine are typical prey,[14] but bottom-living species are taken as discards from commercial fishing. This tern actively follows trawlers, including at night, and during the fishing season trawl discards can constitute 70% of its diet.[32] Prawn fishing is particularly productive in providing extra food, since prawns usually represent only 10–20% of the catch, the remaining being bycatch, mainly fish such as cardinalfish and gobies.[32]

Bycatch from prawn fishing can provide extra food

A study of an area of the Great Barrier Reef where the number of breeding great crested terns has grown ten-fold, probably due to extra food from trawl by-catch, suggested that lesser crested and sooty terns have moved away and now breed on a part of the reef where fishing is banned. It is possible that the large increase in the number of greater crested terns may have affected other species through competition for food and nesting sites.[34]

Terns have red oil droplets in the cone cells of the retinas of their eyes. This improves contrast and sharpens distance vision, especially in hazy conditions.[35] Birds that have to see through an air/water interface, such as terns and gulls, have more strongly coloured carotenoid pigments in the cone oil drops than other avian species.[36] The improved eyesight helps terns to locate shoals of fish, although it is uncertain whether they are sighting the phytoplankton on which the fish feed, or observing other terns diving for food.[37] Tern's eyes are not particularly ultraviolet sensitive, an adaptation more suited to terrestrial feeders like the gulls.[38]


The greater crested tern has a widespread distribution range, estimated at 1–10 million square kilometres (0.4–3.8 million square miles). The population has not been quantified, but it is not believed to approach the thresholds for either the size criterion (fewer than 10,000 mature individuals) or the population decline criterion (declining more than 30% in ten years or three generations) of the IUCN Red List. For these reasons, the species is evaluated as being of Least Concern at the global level.[1] However, there are concerns for populations in some areas such as the Gulf of Thailand where the species no longer breeds, and in Indonesia where egg harvesting has caused declines.[10]

All subspecies except T. b. cristata are covered under the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA).[39] Parties to the Agreement are required to engage in a wide range of conservation strategies described in a detailed action plan. The plan is intended to address key issues such as species and habitat conservation, management of human activities, research, education, and implementation.[40]


  1. ^ a b BirdLife International (2012). "Sterna bergii". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ Greater crested tern on Avibase
  3. ^ Gill, F; Donsker D (eds). "IOC World Bird Names (v 2.11)". International Ornithologists' Union.  Retrieved 28 February 2012
  4. ^ Snow & Perrin (1998) 764
  5. ^ Adapted from Bridge et al. (2005). This study did not include the Chinese crested tern
  6. ^ This genus had originally been created by Heinrich Boie in 1822, but had been abandoned until the Bridge (2005) study confirmed the need for a separate genus for the crested terns.
  7. ^ a b Bridge, Eli S.; Jones, Andrew W.; Baker, Allan J. (2005). "A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution" (PDF). Molecular Phylogenetics and Evolution 35 (2): 459–469. doi:10.1016/j.ympev.2004.12.010. PMID 15804415. 
  8. ^ Mees, G. F. (1975). "Identiteit en status van Sterna bernsteini Schlegel". Ardea (in Dutch) 63: 78–86. 
  9. ^ a b Higgins & Davies (1996) 605–609
  10. ^ a b c d e f g h Del Hoyo et al. (1996) 648
  11. ^ Parentheses indicate originally described under a different name
  12. ^ a b c Harrison (1988) 383
  13. ^ a b c d e f g Olsen & Larsson (1995) 35–42
  14. ^ a b c d e f g h i j k Cooper (2006) 760–764
  15. ^ Not considered by Olsen & Larsson (1995)
  16. ^ a b c d e f Snow & Perrin (1998) 770–771
  17. ^ Skerrett, Adrian; Bullock, I.; Disley, T. (2001). Birds of Seychelles. London: Christopher Helm. p. 230. ISBN 0-7136-3973-3. 
  18. ^ Pratt, H. Douglas; Bruner, P.; Berrett, D. (1987). The Birds of Hawaii and the Tropical Pacific. Princeton: Princeton University Press. p. 178. ISBN 0-691-08402-5. 
  19. ^ a b Carrick, R.; Wheeler, W. R.; Murray, M. D. (1957). "Seasonal dispersal and mortality in the Silver Gull, Larus novae-hollandiae Stephens, and Crested tern, Sterna bergii Lichstein, in Australia". Wildlife Research 2 (2): 116–144. doi:10.1071/CWR9570116. 
  20. ^ American Ornithologists' Union (1998). Check-list of North American Birds (PDF extract) (7th ed.). Washington, D.C.: American Ornithologists' Union. p. 198. ISBN 1-891276-00-X. 
  21. ^ a b c "Great Crested Tern Sterna bergii". BirdLife Species Factsheet (additional data). BirdLife International. Retrieved 7 July 2008. 
  22. ^ Robertson C.J.R.; Medway, D. G. "New Zealand recognized bird names (NZRBN)" (PDF). Ornithological Society of New Zealand. 
  23. ^ Higgins & Davies (1996) 610–611
  24. ^ Walker, T. A. (1992). "A record Crested Tern Sterna bergii colony and concentrated breeding by seabirds in the Gulf of Carpentaria". Emu 92 (3): 152–156. doi:10.1071/MU9920152. 
  25. ^ Fisher, James; Lockley, R. M. (1989). Sea‑Birds (Collins New Naturalist series). London: Bloomsbury Books. pp. 155–156. ISBN 1-870630-88-2. 
  26. ^ "Crested Tern". Fact Sheets. Australian Museum. Retrieved 5 July 2008. 
  27. ^ Dunlop, J. N. (1987). "Social-behavior and colony formation in a population of crested terns, Sterna bergii, in southwestern Australia". Australian Wildlife Research 14 (4): 529–540. doi:10.1071/WR9870529. 
  28. ^ a b Langham, N.P.E.; Hulsman, K (1986). "The Breeding Biology of the Crested Tern Sterna bergii". Emu 86: 23–32. doi:10.1071/MU9860023. 
  29. ^ Davies, S. J. J. F.; Carrick, R (1962). "On the ability of crested terns, Sterna bergii, to recognize their own chicks". Australian Journal of Zoology 10 (2): 171–177. doi:10.1071/ZO9620171. 
  30. ^ Crawford, R. J. M.; Dyer B. (2000). "Swift Terns Sterna bergii breeding on roofs and at other new localities in southern Africa" (PDF). Marine Ornithology 28: 123–124. 
  31. ^ a b le Roux, Janine. "Swift Tern Sterna bergii". Avian Demography Unit, University of Cape Town. Retrieved 5 July 2008. 
  32. ^ a b c d Blaber, S. J. M.; Milton, D. A.; Smith, G. C.; Farmer, M. J. (November 1995). "Trawl discards in the diets of tropical seabirds of the northern Great Barrier Reef, Australia" (PDF). Marine Ecology Progress Series 127: 1–13. doi:10.3354/meps127001. 
  33. ^ Parsons, Nola J.; Tjørve, Kathy M. C.; Underhill, Les G.; Strauss, Venessa (April 2006). "The rehabilitation of Swift Terns Sterna bergii incapacitated by marine foam on Robben Island, South Africa". Ostrich - Journal of African Ornithology 77 (1–2): 95–98. doi:10.2989/00306520609485514. 
  34. ^ Blaber, S. J. M.; Milton, D. A.; Farmer, M. J.; Smith, G. C. (1998). "Seabird breeding populations on the far northern Great Barrier Reef, Australia: trends and influences". Emu 98: 44–57. doi:10.1071/MU98006. 
  35. ^ Sinclair, Sandra (1985). How Animals See: Other Visions of Our World. Beckenham, Kent: Croom Helm. pp. 93–95. ISBN 0-7099-3336-3. 
  36. ^ Varela, F. J.; Palacios, A. G.; Goldsmith T. M. (1993) "Vision, Brain, and Behavior in Birds" in Harris, Philip; Bischof, Hans-Joachim Vision, Brain, and Behavior in Birds: a comparative review Cambridge, Massachusetts: MIT Press 77–94 ISBN 0-262-24036-X
  37. ^ Lythgoe, J. N. (1979). The Ecology of Vision. Oxford: Clarendon Press. pp. 180–183. ISBN 0-19-854529-0. 
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