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Overview

Comprehensive Description

The specific name of the bridled tern, anathetus, is derived from the Greek for senseless or stupid, a reference to the ease with which hungry sailors captured this relatively docile seabird. Relative to other terns, the bridled tern is of average size, with a deeply-forked tail and long narrow wings. During the breeding season, the upperparts of its plumage, including the back, wings and tail, are brownish grey, while the underparts are generally whitish. The crown and nape are black but the forehead is marked by a triangular white patch that extends above and behind the eyes. The bill is about as long as the head and is black in colour, as are the legs and feet. Outside of the breeding season, the bridled tern is slightly paler, with its black crown streaked white and brown, and the dark feathers of the upperparts having white-tips, giving it a peppered appearance. Juveniles are similar in appearance to the adults but have a paler, streaked crown and upperparts heavily scaled with white and buff. Four to six subspecies, differing only slightly in appearance but occupying different parts of the bridled tern’s overall range, are variably recognised.

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Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: off northwestern Costa Rica and possibly Panama; Formosa to Australia; Bahamas (Sprunt 1984); Cuba; Jamaica; Hispaniola; Puerto Rico (Mona [erroneous? van Halewyn and Norton 1984], Desecheo, off Culebra, elsewhere?); Virgin Islands; Lesser Antilles; Belize; off Venezuela; off Mauritania; Gulf of Guinea; Indian Ocean islands. Nested on Pelican Shoal (near Boca Chica Key), Monroe County, Florida, in late 1980s/early 1990s (Hoffman et al. 1993, Am. Birds 47:379-381). NON-BREEDING: at sea in Pacific off Middle America, and widely in western Pacific; in Atlantic-Caribbean region widely in West Indies, north along southeastern U.S., especially after storms, rarely along northern coast of Venezuela; Indian Ocean (AOU 1983).

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Range Description

The Bridled Tern is a bird of the tropical oceans. It breeds off the Pacific and Atlantic coast of Central America including the Carribean, off small areas of western Africa, around Arabia and eastern Africa down to South Africa, off the coast of India, and in much of south-east Asia and Australasia excluding southern Australia and New Zealand (del Hoyo et al. 1996).
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Subspecies and Distribution:


    * melanoptera Swainson, 1837 - W Africa. * fuligula Lichtenstein, 1844 - Red Sea and E Africa through Persian Gulf and Arabian Sea to W India. * antarctica Lesson, 1831 - Madagascar, Aldabra, Seychelles and Mascarenes through Maldives to Andaman Is. * anaethetus Scopoli, 1786 - extreme S Japan (S Ryukyu Is) and Taiwan S through Philippines and Indonesia to Australia, including Lord Howe I and Norfolk I. * nelsoni Ridgway, 1919 - W coast of Mexico and Central America. * recognita (Mathews, 1912) - West Indies, Belize and islands off N Venezuela.


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Physical Description

Size

Length: 38 cm

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33-38 cm, 95-150 g, wingspan 76-81 cm

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Diagnostic Description

The specific name of the bridled tern, anathetus, is derived from the Greek for senseless or stupid, a reference to the ease with which hungry sailors captured this relatively docile seabird. Relative to other terns, the bridled tern is of average size, with a deeply-forked tail and long narrow wings. During the breeding season, the upperparts of its plumage, including the back, wings and tail, are brownish grey, while the underparts are generally whitish. The crown and nape are black but the forehead is marked by a triangular white patch that extends above and behind the eyes. The bill is about as long as the head and is black in colour, as are the legs and feet. Outside of the breeding season, the bridled tern is slightly paler, with its black crown streaked white and brown, and the dark feathers of the upperparts having white-tips, giving it a peppered appearance. Juveniles are similar in appearance to the adults but have a paler, streaked crown and upperparts heavily scaled with white and buff. Four to six subspecies, differing only slightly in appearance but occupying different parts of the bridled tern’s overall range, are variably recognised.

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Type Information

Type for Sterna anaethetus melanoptera
Catalog Number: USNM 30844
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Sex/Stage: unknown; Adult
Preparation: Skin: Whole
Collector(s): O. Salvin
Year Collected: 1862
Locality: Saddle Cay, Islet At the S End of Lighthouse Reef, E of Turneffe Island, Belize, North America
  • Type: Coues. July-October 1864. Ibis. (1) 6: 392 (footnote).
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Ecology

Habitat

Comments: NON-BREEDING: Mostly pelagic; often around rocky offshore cays. Rests at sea usually on driftwood or flotsam, sometimes on water (Stiles and Skutch 1989). BREEDING: Nests usually in rocky areas or on coral, occasionally on sand, generally in crevices, on ledges, or partially concealed (e.g., among grass tussocks), usually on steep edge of offshore cay.

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Habitat and Ecology

Habitat and Ecology
Behaviour Most populations are migratory and dispersive (Higgins and Davies 1996, Haney et al. 1999) and abandon their breeding sites at the end of the breeding season to overwinter at sea (Haney et al. 1999). Its detailed migratory movements are largely unknown however (del Hoyo et al. 1996) and some populations in the Indian Ocean are entirely sedentary or only partially migratory (Haney et al. 1999). The timing of breeding varies geographically, most populations breeding annually in groups of 2-30 pairs (sometimes up to 400-2,000 pairs) (del Hoyo et al. 1996) that are not strictly colonial but involve solitary pairs congregating in suitable habitat (Haney et al. 1999). When nesting the species often associates with nesting Sterna fuscata or Sterna bergii (del Hoyo et al. 1996). After breeding the adults and newly fledged young leave the breeding colonies in loose flocks (Higgins and Davies 1996) and migrate alone, in small groups of 10-12 individuals or more rarely in larger groups of up to 200 individuals (Haney et al. 1999). Outside of the breeding season the species is thought to occur singly (Higgins and Davies 1996). Habitat The species inhabits offshore tropical and subtropical seas (Higgins and Davies 1996, del Hoyo et al. 1996). Breeding It breeds on the periphery of vegetated coastal and continental (Haney et al. 1999) coral, rock or rubble islands and beaches (Higgins and Davies 1996, del Hoyo et al. 1996, Haney et al. 1999), volcanic stacks and exposed reefs (Haney et al. 1999), foraging inshore and up to 50 km offshore (although mostly within 15 km of land) (del Hoyo et al. 1996) and feeding from the surface of the water or up to 20 cm below it (Higgins and Davies 1996). Non-breeding Away from the breeding grounds the species is entirely pelagic and often associates with patches of macroalgae (e.g. Sargassum spp.) or flotsam (Haney et al. 1999) which it uses for perching (del Hoyo et al. 1996). Its marine distribution is therefore linked to small- and medium-scale oceanographic features where water circulation aggregates such floating matter into patches (Haney et al. 1999). Diet Its diet consists predominantly of squid and surface-schooling fish less than 6 cm long as well as crustaceans and occasionally aquatic insects (del Hoyo et al. 1996) or molluscs (Higgins and Davies 1996). Breeding site The nest is a scrape or depression in shingle or sand (Higgins and Davies 1996) that may be freshly excavated or re-used from a previous season (Higgins and Davies 1996). Nests are placed in a variety of concealed locations (Higgins and Davies 1996, del Hoyo et al. 1996) around the rim of oceanic islands (del Hoyo et al. 1996), including natural cavities amongst rocks or coral rubble, in vegetation (Higgins and Davies 1996, del Hoyo et al. 1996) (up to 75 % ground cover) (Higgins and Davies 1996), in a crevice or cave up to 1.5 m deep, under a cliff ledge or on the ground beneath low bushes or shrubs (Higgins and Davies 1996). The species is not strictly colonial but solitary pairs usually congregate in suitable habitats (Haney et al. 1999) with neighbouring nests spaced according to nest-site availability (usually 1-5 m apart, minimum 30 cm) (del Hoyo et al. 1996). Management information The species will become habituated to human presence in sites exposed to long term visitation, especially where human movements are predictable, groups sizes are kept consistent and human behaviour is reliable (Haney et al. 1999). Additional measures to reduce human disturbance of nesting colonies includes the erection of barriers and signs, the provision of walkways, and the supervision and education of vistors (Haney et al. 1999).

Systems
  • Terrestrial
  • Marine
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Depth range based on 316 specimens in 1 taxon.
Water temperature and chemistry ranges based on 305 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 11.710 - 28.545
  Nitrate (umol/L): 0.038 - 2.407
  Salinity (PPS): 32.426 - 36.319
  Oxygen (ml/l): 4.577 - 6.349
  Phosphate (umol/l): 0.063 - 0.515
  Silicate (umol/l): 0.769 - 3.819

Graphical representation

Temperature range (°C): 11.710 - 28.545

Nitrate (umol/L): 0.038 - 2.407

Salinity (PPS): 32.426 - 36.319

Oxygen (ml/l): 4.577 - 6.349

Phosphate (umol/l): 0.063 - 0.515

Silicate (umol/l): 0.769 - 3.819
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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The bridled tern breeds on coral, rock, or sandy shorelines, and forages over inshore waters and up to 50 kilometres offshore.

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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Dives or swoops to pluck small fishes, crustaceans, squids, or marine water-striders from surface (Stiles and Skutch 1989).

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It feeds mainly on surface-schooling fish, which it catches by diving head first into the water, or by swooping low over the sea to collect prey from the surface. As an alternative it will rest on the surface and catch fish merely by dipping its head or bill into the water. Aside from fish, the bridled tern also takes small amounts of squid and crustaceans, and occasionally aquatic insects.

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General Ecology

Nonbreeding: singly or in small loose groups.

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Life History and Behavior

Behavior

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Reproduction

Eggs laid mid-April to late June in Bahamas (Terres 1980), May-August in Puerto Rico and Virgin Islands (Raffaele 1983); nests May-July in Costa Rica (Stiles and Skutch 1989), April-July in Trinidad/Tobago. In Florida, eggs have been observed in June-July, chick in July. Clutch size 1. Incubation by both sexes (Hilty and Brown 1986). Breeds in small loose aggregations (van Halewyn and Norton 1984).

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The timing of the breeding season varies geographically, but most populations breed in small groups ranging in size from 2 to 30 pairs, but sometimes comprising several hundred. The nests are often distributed in vegetation, rock or rubble, where they can be concealed to reduce the chances of predation. Each breeding pair produces just a single egg which is incubated for 28 to 30 days before hatching. The young fledge when around 50 to 65 days old, but remain dependent on the parent birds for another 30 to 35 days.

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Onychoprion anaethetus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 3 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

TCTATACTTAATTTTCGGTGCATGAGCCGGTATAGTAGGTACTGCCCTTAGCTTACTCATTCGTGCGGAACTAGGCCAACCAGGGACCCTTCTAGGAGACGACCAAATCTACAATGTAATTGTCACCGCCCACGCCTTCGTAATAATTTTCTTCATAGTAATGCCAATTATAATTGGTGGTTTCGGAAACTGATTAGTACCACTTATAATCGGTGCCCCCGACATGGCATTCCCACGCATAAACAACATAAGCTTCTGACTACTACCCCCATCATTTTTACTTCTTCTAGCCTCCTCCACAGTAGAAGCTGGGGCTGGAACAGGATGGACCGTATATCCTCCCCTAGCCGGTAACCTAGCCCATGCCGGAGCTTCAGTGGACTTAGCAATCTTCTCCCTCCATCTAGCAGGTGTATCCTCTATTTTAGGTGCTATCAACTTCATCACCACAGCCATTAACATAAAACCTCCTGCCCTCTCACAATACCAAACTCCACTATTTGTATGATCCGTACTTATTACTGCCGTCCTACTACTACTCTCACTCCCAGTACTTGCTGCCGGCATCACTATGCTATTAACAGATCGAAACCTAAACACAACATTCTTCGATCCTGCCGGAGGTGGTGACCCAGTACTATATCAACATCTCNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
-- end --

Download FASTA File
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Statistics of barcoding coverage: Onychoprion anaethetus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 4
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N1B,N3N : N1B: Critically Imperiled - Breeding, N3N: Vulnerable - Nonbreeding

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s

Justification
This species has a very 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 is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds 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.

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Not Threatened.

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Population

Population
The global population is estimated to number c.610,000-1,500,000 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.10,000-1 million breeding pairs and > c.1,000 individuals on migration in Taiwan and < c.100 breeding pairs and < c.50 individuals on migration in Japan (Brazil 2009).

Population Trend
Unknown
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Threats

Major Threats
The species is vulnerable to the effects of oil spills and is highly vulnerable to the accidental introduction of domestic cats Felis catus to offshore breeding islands (Haney et al. 1999). It has also been known to abandon breeding colonies when subject to severe human disturbance (although at sites exposed to long-term visitation it may become habituated to continuous and predictable human presence and activity) (Haney et al. 1999). Utilisation Eggs are harvested for subsistence in the Bahamas and the West Indies, and eggs and chicks are harvested on some islands in the Pacific by local residents and coastal shipping crews (Haney et al. 1999).
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Wikipedia

Bridled Tern

The bridled tern (Onychoprion anaethetus, formerly Sterna anaethetus - see Bridge et al., 2005) is a seabird of the tern family Sternidae. It is a bird of the tropical oceans.

Description[edit]

In non-breeding plumage

This is a medium-sized tern, at 30–32 cm in length and with a 77–81 cm wingspan similar to the common tern in size, but more heavily built. The wings and deeply forked tail are long, and it has dark grey upperparts and white underparts. The forehead and eyebrows are white, as is a striking collar on the hindneck. It has black legs and bill. Juvenile bridled terns are scaly grey above and pale below.

This species is unlikely to be confused with any tern apart from the similarly dark-backed sooty tern and the spectacled tern from the Tropical Pacific. It is paler-backed than that sooty, (but not as pale as the grey-backed) and has a narrower white forehead and a pale neck collar.

Distribution and movements[edit]

This bird is migratory and dispersive, wintering more widely through the tropical oceans. It has markedly marine habits compared to most terns. The Atlantic subspecies melanopters breeds in Mexico, the Caribbean and west Africa; other races occur around the Arabia and in Southeast Asia and Australasia, but the exact number of valid subspecies is disputed. It is a rare vagrant to western Europe.

Breeding[edit]

This species breeds in colonies on rocky islands. It nests in a ground scrape or hole and lays one egg. It feeds by plunge-diving for fish in marine environments, but will also pick from the surface like the black tern and the gull-billed tern. 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.

Lady Elliot Island, Qld, Australia


Various views and plumages[edit]

References[edit]

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Names and Taxonomy

Taxonomy

Comments: Formerly (AOU 1983, 1998) included in the genus Sterna but separated on the basis of genetic data that correspond to plumage patterns (Bridge et al. 2005).

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