View source for Tern

{{short description|Family of seabirds}}
{{other uses}}
{{Featured article}}
{{EngvarB|date=July 2022}}
{{Use dmy dates|date=July 2022}}
{{Automatic taxobox
| name                = Terns
| fossil_range        = [[Early Miocene]] to present
| image               = 3-point tern (Sandwich, Common & Roseate Terns, St Mary's Island, Northumberland).jpg
| image_caption       = A [[Sandwich tern]], a [[common tern]] and a [[roseate tern]] together, Northumberland, UK
| taxon               = Sterninae
| authority           =  [[Charles Lucien Bonaparte|Bonaparte]], 1838
| subdivision_ranks   = Genera
| subdivision         =
*''[[Anous]]''
*''[[marsh tern|Chlidonias]]''
*''[[Gelochelidon]]''
*''[[Gygis]]''
*''[[Caspian tern|Hydroprogne]]''
*''[[Inca tern|Larosterna]]''
*''[[Onychoprion]]''
*''[[Large-billed tern|Phaetusa]]''
*''[[Sterna]]''
*''[[Sternula]]''
*''[[Thalasseus]]''
}}
[[File:Birds of Sweden 2016 07.jpg|thumb|[[Common tern]] in flight]]
[[File:Birds of Sweden 2016 08.jpg|thumb|Common tern in flight]]
'''Terns''' are [[seabird]]s in the [[family (biology)|family]] '''[[Laridae]]''', subfamily '''Sterninae''', that have a worldwide distribution and are normally found near the [[sea]], [[river]]s, or [[wetland]]s. Terns are treated in eleven [[genus|genera]] in a subgroup of the family Laridae, which also includes several genera of [[gull]]s and the [[Skimmer (bird)|skimmers]] (''Rynchops''). They are slender, lightly built birds with long, forked tails, narrow wings, long bills, and relatively short legs. Most species are pale grey above and white below with a contrasting black cap to the head, but the [[marsh tern]]s, the [[black-bellied tern]], the [[Inca tern]], and some [[Noddy (tern)|noddies]] have dark body [[plumage]] for at least part of the year. The sexes are identical in appearance, but young birds are readily distinguishable from adults. Terns have a non-breeding plumage, which usually involves a white forehead and much-reduced black cap.
Terns are long-lived birds and are relatively free from natural predators and [[parasites]]; most species are declining in numbers due directly or indirectly to human activities, including habitat loss, pollution, disturbance, and predation by [[introduced mammal]]s. The [[Chinese crested tern]] is [[critically endangered]] and three other species are classed as [[endangered species|endangered]]. International agreements provide a measure of protection, but adults and eggs of some species are still used for food in the tropics.
==Description==
[[File:Larosterna inca4.jpg|thumb|The plumage of the [[Inca tern]] is the most atypical of the group.]]
Terns range in size from the [[least tern]], at {{convert|23|cm|in|abbr=on}} in length and weighing {{convert|30|–|45|g|oz|abbr=on}},<ref name= Maehr>Maehr & Kale (2005) p. 111.</ref><ref name= olsen136>Olsen & Larsson (1995) p. 136.</ref> to the [[Caspian tern]] at {{convert|48|–|56|cm|in|abbr=on}}, {{convert|500|–|700|g|oz|abbr=on}}.<ref name= harrisoncasp>Harrison (1988) p. 368.</ref><ref>Olsen & Larsson (1995) p. 25.</ref> They are longer-billed, lighter-bodied, and more streamlined than gulls, and their long tails and long narrow wings give them an elegance in flight. Male and female plumages are identical, although the male can be 2–5% larger than the female and often has a relatively larger bill. Sea terns have deeply forked tails, and at least a shallow "V" is shown by all other species.<ref name= HBW/> The noddies (genera ''Anous'', ''Procelsterna'' and ''Gygis'') have unusual notched-wedge shaped tails, the longest tail feathers being the middle-outer, rather than the central or outermost.<ref name= harrison388>Harrison (1988) pp. 387–390.</ref><ref name= Hutton>Hutton & Drummond (2011) p. 226.</ref> Although their legs are short, terns can run well. They rarely swim, despite having webbed feet, usually landing on water only to bathe.<ref name= HBW/>
The majority of sea terns have light grey or white body [[plumage]] as adults, with a black cap to the head. The legs and bill are various combinations of red, orange, yellow, or black depending on species. The pale plumage is conspicuous from a distance at sea, and may attract other birds to a good feeding area for these fish-eating species. When seen against the sky, the white underparts also help to hide the hunting bird from its intended prey. The Inca tern has mainly dark plumage, and three species that mainly eat insects, [[black tern]], [[white-winged tern]], and [[black-bellied tern]], have black underparts in the breeding season. Three of the ''Anous'' noddies have dark plumage with a pale head cap, the other two (formerly separated in the genus ''Procelsterna'' paler grey. The reason for their dark plumage is unknown, but it has been suggested that in tropical areas, where food resources are scarce, the less conspicuous colouration makes it harder for other noddies to detect a feeding bird.<ref name= simmons>{{cite journal | last= Simmons | first= Keith E L | year=1972 | title= Some adaptive features of seabird plumage types | journal= British Birds | volume= 65 | issue =11 | pages=465–479 | url =http://www.britishbirds.co.uk/search?model=pdf&id=4571 }}</ref> Plumage type, especially the head pattern, is linked to the [[Phylogenetics|phylogeny]] of the terns, and the pale-capped, dark-bodied noddies are believed to have diverged earlier than the other genera from an ancestral white-headed gull, followed by the partially black-headed ''[[Onychoprion]]'' and ''[[Sternula]]'' groupings.<ref name= bridge/><ref name="Cerny">{{cite journal |last1=Černý |first1=David |last2=Natale |first2=Rossy |title=Comprehensive taxon sampling and vetted fossils help clarify the time tree of shorebirds (Aves, Charadriiformes) |journal=Molecular Phylogenetics and Evolution |date=2022 |volume=177 |doi=10.1016/j.ympev.2022.107620 |bibcode=2022MolPE.17707620C |url=https://www.sciencedirect.com/science/article/abs/pii/S1055790322002330 |access-date=2024-07-24}}</ref>
Juvenile terns typically have brown- or yellow-tinged upperparts, and the feathers have dark edges that give the plumage a scaly appearance. They have dark bands on the wings and short tails. In most species, the subsequent [[moulting|moult]] does not start until after migration, the plumage then becoming more like the adult, but with some retained juvenile feathers and a white forehead with only a partial dark cap. By the second summer, the appearance is very like the adult, and full mature plumage is usually attained by the third year. After breeding, terns moult into a winter plumage, typically showing a white forehead. Heavily worn or aberrant plumages such as [[melanism]] and [[albinism]] are much rarer in terns than in gulls.<ref>Olsen & Larsson (1995) pp. 6–9.</ref>
=== Voice ===
{{listen|filename=Sterna-hirundo-002.ogg|title=Common tern (80 s)|description=}}
Terns have a wide repertoire of vocalisations. For example, the [[common tern]] has a distinctive [[alarm signal|alarm]], ''kee-yah'', also used as a warning to intruders, and a shorter ''kyar'', given as an individual takes flight in response to a more serious threat; this quietens the usually noisy colony while its residents assess the danger. Other calls include a down-slurred ''keeur'' given when an adult is approaching the nest with a fish, and a ''kip'' uttered during social contact.<ref name=hume68>Hume (1993) pp. 68–75.</ref> Parents and chicks can locate one another by call,<ref name= burton>Burton (1985) p. 123.</ref> and [[sibling]]s also recognise each other's vocalisations from about the twelfth day after hatching, which helps to keep the brood together.<ref name= sibling>{{cite journal | last= Burger | first= Joanna | author2=Gochfeld, Michael| author3=Boarman, William I | year=1988 | title= Experimental evidence for sibling recognition in Common Terns (''Sterna hirundo'') | journal= Auk | volume= 105 | issue = 1 | pages= 142–148 | jstor=4087337 | doi= 10.1093/auk/105.1.142 }}</ref><ref name=Stevenson>{{cite journal |last=Stevenson |first=J G |author2=Hutchison, R E |author3=Hutchison, J B |author4=Bertram B C R |author5= Thorpe, W H  |year=1970 |title=Individual recognition by auditory cues in the Common Tern (''Sterna hirundo'') |journal=Nature |volume=226 |issue=5245 |pages=562–563 |doi=10.1038/226562a0 |pmid=16057385|bibcode=1970Natur.226..562S |s2cid=4181980 }}</ref>
Vocal differences reinforce species separation between closely related birds such as the least and [[little tern]]s,<ref name= Massey>{{cite journal |last= Massey |first= Barbara W |year=1976 |title= Vocal Differences between American Least Terns and the European Little Tern | journal= The Auk | volume= 93| pages=760–773 |jstor=4085004 |issue=4}}</ref> and can help humans distinguish similar species, such as common and [[arctic tern]]s, since flight calls are unique to each species.<ref name= const>Constantine (2006) pp. 73–77.</ref><ref name=burger/>
== Taxonomy ==
The bird [[order (biology)|order]] [[Charadriiformes]] contains 18 [[seabird|coastal seabird]] and [[wader]] [[family (biology)|families]]. Within the order, the terns form a lineage with the [[gull]]s, and, less closely, with the [[Skimmer (bird)|skimmer]]s, [[skua]]s, and [[auk]]s.<ref>{{cite journal | last1 = Paton | first1 = Tara A | last2 = Baker | first2 = Allan J | last3 = Groth | first3 = Jeffrey G | last4 = Barrowclough | first4 = George F | year = 2003 | title = RAG-1 sequences resolve phylogenetic relationships within charadriiform birds |journal = Molecular Phylogenetics and Evolution | volume = 29 | pages = 268–278 | doi = 10.1016/S1055-7903(03)00098-8 | pmid = 13678682 | issue = 2 | bibcode = 2003MolPE..29..268P }}</ref><ref name=tuinen>{{cite journal | last= van Tuinen | first= Marcel | author2=Waterhouse, David M| author3=Dyke, Gareth J | year= 2004 | title= Avian molecular systematics on the rebound: a fresh look at modern shorebird phylogenetic relationships | journal= Journal of Avian Biology | volume= 35 | issue = 3 | pages= 191–194 |doi = 10.1111/j.0908-8857.2004.03362.x}}</ref> Early authors such as [[Conrad Gessner]], [[Francis Willughby]], and [[William Turner (naturalist)|William Turner]] did not clearly separate terns from gulls,<ref name = hume12/> but [[Carl Linnaeus|Linnaeus]] recognised the distinction in his 1758 ''[[Systema Naturae]]'', placing the gulls in the genus '' [[Larus]]'' and the terns in ''Sterna''. He gave ''Sterna'' the description ''rostrum subulatum'', "[[bradawl|awl-shaped]] bill", referring to the long, pointed bills typical of this group of birds, a feature that distinguishes them from the thicker-billed gulls.<ref name = linn84>Linnaeus (1758) p. 84.</ref><ref name= job338>Jobling (2010) p. 338.</ref><ref>{{cite book | title = The Chambers Dictionary |edition=ninth | year = 2006 | publisher = Chambers | location = Edinburgh | isbn = 0-550-10105-5 | url-access = registration | url = https://archive.org/details/chambersdictiona0000unse_x2v6 |page=1510}}.</ref> Behaviour and [[Morphology (biology)|morphology]] suggest that the terns are more closely related to the gulls than to the skimmers or skuas, and although [[Charles Lucien Bonaparte]] created the family Sternidae for the terns in 1838, for many years they were considered to be a subfamily, Sterninae, of the gull family, Laridae. Relationships between various tern species, and between the terns and the other Charadriiformes, were formerly difficult to resolve because of a poor [[fossil]] record and the misidentification of some finds.<ref name= HBW>Gochfeld & Burger (1996) pp. 624–645.</ref><ref name= pietri>{{cite journal |last= de Pietri |first= Vanesa L | author2=Costeur, Loïc| author3=Güntert, Marcel| author4=Mayr, Gerald |year=2011 |title= A revision of the Lari (Aves, Charadriiformes) from the early Miocene of Saint-Gérand-le-Puy (Allier, France) | journal= Journal of Vertebrate Paleontology | volume=31 | pages=812–828 |doi=10.1080/02724634.2011.586663|issue= 4|bibcode= 2011JVPal..31..812D |s2cid= 84758271 }}</ref>
Following [[gene]]tic research in the early twenty-first century, the terns were historically treated as a separate family, Sternidae.<ref name = paton>{{cite journal | last1 = Paton | first1 = Tara A | last2 = Baker | first2 = Allan J | year = 2006 | title = Sequences from 14 mitochondrial genes provide a well-supported phylogeny of the Charadriiform birds congruent with the nuclear RAG-1 tree | journal = Molecular Phylogenetics and Evolution | volume = 39 | issue = 3| pages = 657–667 | doi = 10.1016/j.ympev.2006.01.011 | pmid = 16531074 | bibcode = 2006MolPE..39..657P }}</ref><ref>{{cite journal | last1 = Thomas | first1 = Gavin H | last2 = Wills | first2 = Matthew A | last3 = Székely | first3 = Tamás | year = 2004 | title = A supertree approach to shorebird phylogeny | journal = [[BMC Evolutionary Biology]] | volume = 4 |page = 28 | doi = 10.1186/1471-2148-4-28 | pmid = 15329156 | pmc=515296 | doi-access = free }}</ref> Most terns were formerly treated as belonging to one large genus, ''[[Sterna]]'', with just a few dark species placed in other genera; in one 1959 paper, only the [[Noddy (tern)|noddies]] and the [[Inca tern]] were excluded from ''Sterna''.<ref name=" Moynihan" >{{cite journal | last= Moynihan | first= M | year= 1959 | title= A revision of the family Laridae | journal= American Museum Novitates | issue= 1928 |pages= 1–42 }}</ref><ref name= collinson>{{cite journal | last= Collinson | first= M | year= 2006 | title= Splitting headaches? Recent taxonomic changes affecting the British and Western Palaearctic lists | journal= [[British Birds (magazine)|British Birds]] | volume= 99 | issue= 6 | pages= 306–323 | url= https://britishbirds.co.uk/wp-content/uploads/article_files/V99/V99_N06/V99_N06_P306_323_A004.pdf | access-date= 17 April 2017 | archive-date= 8 August 2020 | archive-url= https://web.archive.org/web/20200808071132/https://britishbirds.co.uk/wp-content/uploads/article_files/V99/V99_N06/V99_N06_P306_323_A004.pdf | url-status= dead }}</ref> A recent analysis of [[Nucleic acid sequence|DNA sequences]] supported the splitting of ''Sterna'' into several smaller genera.<ref name= collinson/><ref name= bridge>{{cite journal | last= Bridge |first= Eli S | author2= Jones, Andrew W| author3=Baker, Allan J | year= 2005 | title= A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution | journal= Molecular Phylogenetics and Evolution | volume= 35 |issue= 2 | pages= 459–469 | doi = 10.1016/j.ympev.2004.12.010 | pmid=15804415|bibcode= 2005MolPE..35..459B |s2cid= 25027599 }}</ref> One study of part of the [[cytochrome b]] gene sequence found a close relationship between terns and a group of waders in the suborder [[Thinocori]].<ref name= thomas>{{cite journal | last= Thomas | first= Gavin H | author2=Wills, Matthew A| author3=Székely, Tamás | year= 2004 | title= Phylogeny of shorebirds, gulls, and alcids (Aves: Charadrii) from the cytochrome-''b'' gene: parsimony, Bayesian inference, minimum evolution, and quartet puzzling | journal= Molecular Phylogenetics and Evolution | volume= 30 | issue = 3 | pages= 521–526 | doi = 10.1016/S1055-7903(03)00222-7 | pmid=15012936| bibcode= 2004MolPE..30..516T }}</ref> These results are in disagreement with other molecular and morphological studies, and have been interpreted as showing either a large degree of molecular [[convergent evolution]] between the terns and these waders, or the retention of an ancient [[genotype]].<ref name= paton/>
Research in 2007 had suggested that the noddies were not terns at all, but were basal to all the other genera in Laridae,<ref name="Baker">{{cite journal |last1=Baker |first1=Allan J. |last2=Pereira |first2=Sérgio L. |last3=Paton |first3=Tara A. |title=Phylogenetic relationships and divergence times of Charadriiformes genera: multigene evidence for the Cretaceous origin of at least 14 clades of shorebirds |journal=Biology Letters |date=2007 |volume=3 |issue=2 |pages=205–209 |doi=10.1098/rsbl.2006.0606 |pmid=17284401 |pmc=2375939 }}</ref> a taxonomy that was followed by the IOC World Bird List for several years up to 2023, but more comprehensive analysis has now shown that the noddies are basal to only the other terns, not the whole family;<ref name="Cerny"/> this has now been followed by the IOC World Bird List version 14.1 in 2024.
===Etymology===
The word "stearn" was used for these birds in [[Old English]] as early as the eighth century, and appears in the poem ''[[The Seafarer (poem)|The Seafarer]]'', written in the ninth century or earlier. Variants such as "tearn" occurred by the eleventh century, although the older form lingered on in [[Norfolk dialect]] for several centuries.<ref name = hume12>Hume (1993) pp. 12–13.</ref> As now, the term was used for the inland [[black tern]] as well as the marine species.<ref name= job365>Jobling (2010) p. 365.</ref><ref name= lock>Lockwood (1984) pp. 147, 153.</ref> Some authorities consider "tearn" and similar forms to be variants of "stearn",<ref name = hume12/> while others derive the English words from Scandinavian equivalents such as Danish and Norwegian ''terne'' or Swedish ''tärna'', and ultimately from [[Old Norse]] ''þerna''.<ref name=OED1>{{Cite OED |Tern}}</ref><ref>Merriam-Webster (2014)</ref> Linnaeus adopted "stearn" or "sterna" (which the naturalist [[William Turner (naturalist)|William Turner]] had used in 1544 as a Latinisation of an English word, presumably "stern", for the black tern)<ref name=OED2>{{Cite OED |Sterna}}</ref><ref name=Turner78>Turner (1544), p. 78.</ref> or a [[North Germanic languages|North Germanic]] equivalent for his genus name ''Sterna''.<ref name = linn155>Linnaeus (1758) p. 155.</ref>
=== Species ===
The [[cladogram]] shows the relationships between the tern genera, and the currently recognised species, based on [[mitochondrial DNA]] studies, are listed below:<ref name= bridge/>
{{Cladogram|caption=Based on Bridge ''et al'' (2005)<ref name= bridge/> and Černý & Natale (2021)<ref name="Cerny"/>
|clades={{clade|style=font-size:80%;line-height:80%
|1={{clade
|1= ''[[Anous]]''
|2={{clade
|1=''[[Gygis]]''
|2={{clade
|1=''[[Onychoprion]]''
|2={{clade
|1=''[[Sternula]]''
|2={{clade
|1=''[[Phaetusa]]''
|2={{clade
|1={{clade
|1=''[[Gelochelidon]]''
|2=''[[Hydroprogne]]''
}}
|2={{clade
|1=''[[Larosterna]]''
|2={{clade
|1=''[[Chlidonias]]''
|2={{clade
|1=''[[Thalasseus]]''
|2=''[[Sterna]]''
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
{| class="wikitable collapsible"
|-
! Image
! Genus
!Species
|-
|[[File:Anous minutus by Gregg Yan 02.jpg|175px]]
|''[[Anous]]'' {{small|Stephens, 1826}} — [[Noddy (tern)|noddies]]
|
* [[Brown noddy]] (''Anous stolidus'')
* [[Black noddy]] (''A. minutus'' sometimes considered to be a subspecies of the lesser noddy)<ref name= harrison388/>
* [[Lesser noddy]] (''A. tenuirostris'')
* [[Blue noddy]] (''A. cerulea'' this and grey noddy formerly treated in a separate genus ''Procelsterna'')<ref name= harrison388/>
* [[Grey noddy]] (''A. albivitta'' sometimes considered to be a subspecies of the blue noddy)<ref name= harrison388/>
|-
|[[File:White tern with fish.jpg|175px]]
|''[[Gygis]]'' {{small|Wagler, 1832}} — noddies
|
* [[White tern]] (''Gygis alba'' also sometimes called white noddy)
|-
|[[File:Sterna fuscata.JPG|175px]]
|''[[Onychoprion]]'' {{small|Wagler, 1832}} — brown-backed terns
|
* [[Spectacled tern]] (''Onychoprion lunatus'')
* [[Bridled tern]] (''O. anaethetus'')
* [[Sooty tern]] (''O. fuscatus'')
* [[Aleutian tern]] (''O. aleuticus'')
|-
|[[File:Yellow-billed tern Sternula superciliaris.jpg|175px]]
|''[[Sternula]]'' {{small|F. Boie, 1822}} — little white terns
|
* [[Fairy tern]] (''Sternula nereis'')
* [[Damara tern]] (''S. balaenarum'')
* [[Little tern]] (''S. albifrons'')
* [[Saunders's tern]] (''S. saundersi'' formerly considered to be a subspecies of the little tern)<ref name= harrison382>Harrison (1988) p. 382.</ref>
* [[Least tern]] (''S. antillarum'' formerly considered to be a subspecies of the little tern)<ref name= harrison382/>
* [[Yellow-billed tern]] (''S. superciliaris'')
* [[Peruvian tern]] (''S. lorata'')
|-
|[[File:Large-billed Tern (Phaetusa simplex), Pantanal, Brazil.jpg|175px]]
|''[[Phaetusa]]'' {{small|}}  — large-billed terns
|
* [[Large-billed tern]] (''Phaetusa simplex'')
|-
|[[File:Sterna-caspia-010.jpg|175px]]
|''[[Hydroprogne]]'' {{small|Kaup, 1829}}— Caspian terns
|
* [[Caspian tern]] (''Hydroprogne caspia'')
|-
|[[File:Gull-billed Tern in Koonthalulam, India, by Dr. Tejinder Singh Rawal.jpg|175px]]
|''[[Gelochelidon]]''  {{small|Brehm, 1830}} — gull-billed terns
|
* [[Gull-billed tern]] (''Gelochelidon nilotica'')
* [[Australian tern]] (''Gelochelidon macrotarsa'')
|-
|[[File:Larosterna inca3.jpg|175px]]
|''[[Larosterna]]'' {{small|}} — Inca terns
|
* [[Inca tern]] (''Larosterna inca'')
|-
|[[File:White-winged Tern, Mścichy, Biebrzański Park Narodowy, Polska.jpg|175px]]
|''[[marsh tern|Chlidonias]]'' {{small|Rafinesque, 1822}}  — marsh terns
|
* [[Black tern]] (''Chlidonias niger'')
* [[White-winged tern]] (or white-winged black tern ''C. leucopterus'')
* [[Whiskered tern]] (''C. hybridus'')
* [[Black-fronted tern]] (''C. albostriatus'' sometimes placed in ''Sterna'')<ref name = birdlifealbostriata/>
|-
|[[File:2020-07-18 Thalasseus sandvicensis, St Marys Island, Northumberland 01.jpg|175px]]
|''[[Thalasseus]]'' {{small|F. Boie, 1822}} — crested terns
|
* [[Lesser crested tern]] (''Thalasseus bengalensis'')
* [[West African crested tern]] (''Thalasseus albididorsalis'' recently split from ''T. maximus'')<ref name= collinson/>
* [[Royal tern]] (''T. maximus'')
* [[Greater crested tern]] (''T. bergii'' also known as swift tern)
* [[Chinese crested tern]] (''T. bernsteini'')
* [[Elegant tern]] (''T. elegans'')
* [[Sandwich tern]] (''T. sandvicensis'')
* [[Cabot's tern]] (''T. acuflavidus'' recently split from ''T. sandvicensis'')<ref name=ioc>{{cite web| editor1-last=Gill | editor1-first=Frank | editor1-link=Frank Gill (ornithologist) | editor2-last=Donsker | editor2-first=David | year=2019 | title=Sandpipers, snipes, coursers | work=World Bird List Version 9.2 | url=https://www.worldbirdnames.org/bow/sandpipers/ | publisher=International Ornithologists' Union | access-date=25 June 2019 }}</ref>
|-
|[[File:2014-05-18 Sterna hirundo, Killingworth Lake, Northumberland 02.jpg|175px]]
|''[[Sterna]]'' {{small|Linnaeus, 1758}} — large white terns
|
* [[Forster's tern]] (''Sterna forsteri'')
* [[Snowy-crowned tern]] (''S. trudeaui'')
* [[Common tern]] (''S. hirundo'')
* [[Roseate tern]] (''S. dougallii'')
* [[White-fronted tern]] (''S. striata'')
* [[Black-naped tern]] (''S. sumatrana'')
* [[South American tern]] (''S. hirundinacea'')
* [[Antarctic tern]] (''S. vittata'')
* [[Kerguelen tern]] (''S. virgata'')
* [[Arctic tern]] (''S. paradisaea'')
* [[River tern]] (''S. aurantia'')
* [[Black-bellied tern]] (''S. acuticauda'' possibly ''Chlidonias'')<ref name= bridge/>
* [[White-cheeked tern]] (''S. repressa'' possibly ''Chlidonias'')<ref name= bridge/>
|-
|}
In addition to extant species, the fossil record includes a [[Miocene]] [[chronospecies|palaeospecies]], ''[[Sterna milne-edwardsii]]''.<ref name = fossil>{{cite web | title= Fossil record of the Charadriiformes | url= http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/charadriformes/fossils.html | publisher= Palaeobiology and Biodiversity Research Group, University of Bristol | access-date= 13 May 2013 | archive-url= https://web.archive.org/web/20160304023443/http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/charadriformes/fossils.html | archive-date= 4 March 2016 | url-status= dead | df= dmy-all }}</ref>
The genera ''Anous'', ''Procelsterna'' and ''Gygis'' are collectively known as noddies, the ''Chlidonias'' species are the marsh terns,<ref name =HBW/> and all other species comprise the sea terns.<ref name= Barlow>Barlow ''et al.'' (1987) p. 212.</ref><ref name= perrins>Perrins & Arlott (1987) p. 130.</ref>
==Distribution and habitat==
[[File:Chlidonias niger.jpg|thumb|The [[black tern]] breeds on inland marshes.]]
Terns have a worldwide distribution, breeding on all continents including Antarctica. The northernmost and southernmost breeders are the Arctic tern and [[Antarctic tern]] respectively.<ref name= HBW/><ref name= harrison370>Harrison (1988) pp. 370–371.</ref> Many terns breeding in temperate zones are long-distance [[bird migration|migrants]], and the Arctic tern sees more annual daylight than any other animal as it migrates from its northern breeding grounds to Antarctic waters, a return journey of more than {{convert|30,000|km|mi|abbr=on}}. A common tern that hatched in Sweden and was found dead five months later on [[Stewart Island / Rakiura|Stewart Island]], [[New Zealand]], must have flown at least {{convert|25,000|km|mi|abbr=on}}.<ref name= Newton150>Newton (2010) pp. 150–151.</ref> Actual flight distances are, of course, much greater than the shortest possible route. Arctic terns from Greenland were shown by radio [[geolocation]] to average {{convert|70,000|km|mi|abbr=on}} on their annual migrations,<ref name= Egevan>{{cite journal| last= Egevang | first= Carsten |author2=Stenhouse, Iain J |author3=Phillips, Richard A |author4=Petersen, Aevar |author5=Fox, James W |author6= Silk, Janet R D  | year= 2010| title= Tracking of Arctic terns''Sterna paradisaea'' reveals longest animal migration | journal= Proceedings of the National Academy of Sciences | volume= 107 | issue = 5| pages= 2078–2081| url =http://www.arctictern.info/carsten/pdf/egevang_arte-migration_pnas.full.pdf | doi = 10.1073/pnas.0909493107 | pmid=20080662 | pmc=2836663| bibcode= 2010PNAS..107.2078E | doi-access= free }}</ref> while another from the [[Farne Islands]] in [[Northumberland]] tagged 'G82' covered a staggering 96,000 km in just 10 months from the end of one breeding season to the start of the next, travelling not just the length of the Atlantic Ocean and the width of the Indian Ocean, but also half way across the South Pacific to the boundary between the [[Ross Sea|Ross]] and [[Amundsen Sea]]s before returning back west.<ref name="BBC">{{cite news |last1=BBC News |title=Arctic tern in record-breaking migration from Farne Islands |url=https://www.bbc.co.uk/news/uk-england-tyne-36466763 |access-date=2024-07-24 |agency=BBC |date=7 June 2016}}</ref><ref name="Redfern">{{cite journal |last1=Redfern |first1=Chris |last2=Bevan |first2=Richard M. |title=Use of sea ice by arctic terns Sterna paradisaea in Antarctica and impacts of climate change |journal=Journal of Avian Biology |date=2020 |volume=51 |issue=2 |doi=10.1111/jav.02318 |url=https://nsojournals.onlinelibrary.wiley.com/doi/epdf/10.1111/jav.02318 |access-date=24 July 2024}}</ref>
Most terns breed on open sandy or rocky areas on coasts and islands. The [[yellow-billed tern|yellow-billed]], [[Large-billed tern|large-billed]], and [[black-fronted tern]]s breed only on rivers, and common, least and little terns also sometimes use inland locations. The [[marsh tern]]s, [[Trudeau's tern]] and some [[Forster's tern]]s nest in inland marshes. The [[black noddy]] and the [[white tern]] nest above ground level on cliffs or in trees. Migratory terns move to the coast after breeding, and most species winter near land, although some marine species, like the [[Aleutian tern]], may wander far from land. The [[sooty tern]] is entirely oceanic when not breeding, and healthy young birds are not seen on land for up to five years after fledging until they return to breed. They lack waterproof plumage, so they cannot rest on the sea. Where they spend the years prior to breeding is unknown.<ref name= HBW/>
==Behaviour==
The terns are birds of open habitats that typically breed in noisy [[bird colony|colonies]] and lay their eggs on bare ground with little or no nest material. Marsh terns construct floating nests from the vegetation in their wetland habitats, and a few species build simple nests in trees, on cliffs or in crevices. The [[white tern]], uniquely, lays its single egg on a bare tree branch. Depending on the species, one to three eggs make up the [[clutch (eggs)|clutch]]. Most species feed on fish caught by diving from flight, but the marsh terns are insect-eaters, and some large terns will supplement their diet with small land [[vertebrate]]s. Many terns are long-distance [[bird migration|migrants]], and the [[Arctic tern]] may see more daylight in a year than any other animal.
===Breeding===
[[File:Starr 080605-6653 Casuarina equisetifolia.jpg|thumb|left|[[Brown noddy]] nest on stump of ''[[Casuarina equisetifolia]]'']]
Terns are normally [[monogamy in animals|monogamous]], although trios or female-female pairings have been observed in at least three species.<ref name= HBW/><ref name= nisbet>{{cite journal |last= Nisbet |first= Ian C T | author2=Bridge, Eli S| author3=Szczys, Patricia| author4=Heidinger, Britt J |year= 2007|title= Sexual dimorphism, female-female pairs, and test for assortative mating in Common Terns | journal= Waterbirds | volume= 30| pages= 169–179 |doi=10.1675/1524-4695(2007)30[169:sdfpat]2.0.co;2|jstor=4501815 |issue= 2 |s2cid= 85678067 }}</ref> Most terns breed annually and at the same time of year, but some tropical species may nest at intervals shorter than 12 months or [[synchronization|asynchronously]]. Most terns become sexually mature when aged three, although some small species may breed in their second year. Some large sea terns, including the sooty and [[bridled tern]]s, are four or older when they first breed. Terns normally breed in [[Bird colony|colonies]], and are [[philopatry|site-faithful]] if their habitat is sufficiently stable. A few species nest in small or dispersed groups, but most breed in colonies of up to a few hundred pairs, often alongside other seabirds such as gulls or skimmers.<ref name= HBW/> Large tern species tend to form larger colonies,<ref name= burger/> which in the case of the sooty tern can contain up to two million pairs. Large species nest very close together and sit tightly, making it difficult for aerial predators to land among them. Smaller species are less closely packed and [[Mobbing (animal behavior)|mob]] intruders. [[Peruvian tern|Peruvian]] and [[Damara tern]]s have small dispersed colonies and rely on the [[crypsis|cryptic]] plumage of the eggs and young for protection.<ref name= HBW/>
The male selects a [[Territory (animal)|territory]], which he defends against [[conspecificity|conspecifics]], and re-establishes a [[pair bond]] with his mate or attracts a new female if necessary. Courtship involves ritualised flight and ground displays, and the male often presents a fish to his partner. Most species have little or no nest, laying the eggs onto bare ground, but Trudeau's tern, Forster's tern and the marsh terns construct floating nests from the vegetation in their wetland habitats. Black and [[lesser noddy|lesser noddies]] build nests of twigs, feathers and excreta on tree branches, and [[brown noddy|brown]], [[Blue noddy|blue]], and [[Grey noddy|grey noddies]] make rough platforms of grass and seaweed on cliff ledges, in cavities or on other rocky surfaces.<ref name = HBW/><ref name = watling206>Watling (2003) pp. 206–207.</ref> The Inca tern nests in crevices, caves and disused burrows, such as that of a [[Humboldt penguin]].<ref name = birdlifeinca/> The white tern is unique in that it lays its single egg on a bare tree branch.<ref name=NSWNPWS>{{cite web | title= The White Tern ''Gygis alba'' (Sparrman, 1786) | work= Threatened Species Information | url= http://www.environment.nsw.gov.au/resources/nature/tsprofileWhiteTern.pdf | archive-url= https://web.archive.org/web/20080805055833/http://www.environment.nsw.gov.au/resources/nature/tsprofileWhiteTern.pdf | archive-date= 2008-08-05 | publisher= New South Wales National Parks and Wildlife Service | access-date= 15 May 2013 | url-status= dead }}</ref>
Tropical species usually lay just one egg, but two or three is typical in cooler regions if there is an adequate food supply. The time taken to complete the [[clutch (eggs)|clutch]] varies, but for temperate species [[egg incubation|incubation]] takes 21–28&nbsp;days.<ref name= HBW/> The eggs of most gulls and terns are brown
with dark splotches, so they are difficult for predators to spot on the beach.<ref name= burger/> The [[precocial]] chicks [[fledge]] in about four weeks after hatching. Tropical species take longer because of the poorer food supply. Both parents incubate the eggs and feed the chicks, although the female does more incubating and less fishing than her partner.<ref name= HBW/> Young birds migrate with the adults.<ref name= burger/> Terns are generally long-lived birds, with individuals typically returning for 7–10 breeding seasons. Maximum known ages include 34 for an Arctic tern and 32 for a sooty. Although several other species are known to live in captivity for up to 20 years, their greatest recorded ages are underestimates because the birds can outlive their [[bird ringing|rings]].<ref name= HBW/> Interbreeding between tern species is rare, and involves closely related species when it occurs. Hybrids recorded include common tern with roseate, Sandwich with lesser-crested, and black with white-winged.<ref name= olsen110>Olsen & Larsson (1995) p. 10.</ref>
===Feeding===
[[File:Sterna hirundo -Nantucket National Wildlife Refuge, Massachusetts, USA -adult and juvenile-8.jpg|thumb|An adult [[common tern]] bringing a [[sand eel]] to a juvenile]]
Most terns hunt fish by diving, often hovering first, and the particular approach technique used can help to distinguish similar species at a distance.<ref name=humepearson>Hume & Pearson (1993) pp. 54–55.</ref> Sea terns often hunt in association with [[porpoise]]s or predatory fish, such as [[bluefish]], [[tuna]] or [[bonito]]s, since these large marine animals drive the prey to the surface. Sooty terns feed at night as the fish rise to the surface, and are believed to sleep on the wing since they become waterlogged easily. Terns of several species will feed on [[invertebrate]]s, following the plough or hunting on foot on [[mudflat]]s.<ref name=HBW/> The marsh terns normally catch insects in the air or pick them off the surface of fresh water. Other species will sometimes use these techniques if the opportunity arises.<ref name=collins>Svensson ''et al.'' (2009) p. 206.</ref> An individual tern's foraging efficiency increases with its age.<ref name= burger>Burger J; Gochfeld M "Laridae, Sternidae and Rynchopidae" in Steele ''et al.'' (2001) p. 1469–1480.</ref>
The [[gull-billed tern]] is an opportunist predator, taking a wide variety of prey from marine, freshwater and terrestrial habitats. Depending on what is available it will eat small crabs, fish, [[crayfish]], [[grasshopper]]s and other large insects, lizards and [[amphibian]]s. [[Warm-blooded]] prey includes [[mouse|mice]] and the eggs and chicks of other beach-breeding birds; least terns, little terns and members of its own species may be victims.<ref name = qld/><ref name= Erwin>{{cite journal |last= Erwin |first= R Michael | author2=Eyler, T Brian| author3=Hatfield, Jeff S| author4=McGary, Sabrina |year=1998 |title= Diets of nestling Gull-Billed Terns in coastal Virginia| journal= Colonial Waterbirds | volume=21 | pages=323–327 |doi=10.2307/1521644|jstor= 1521644 |issue=3|bibcode= 1998ColWa..21..323E }}</ref><ref name= dies>{{cite journal |last= Dies |first= J Ignacio | author2=Marín, Jennifer| author3=Pérez, Carlos |year=2005 |title= Diet of nesting Gull-Billed Terns in eastern Spain| journal= Waterbirds | volume=28 | pages=106–109 |doi=10.1675/1524-4695(2005)028[0106:dongti]2.0.co;2|jstor=1522321 |issue=1|s2cid= 85996773 }}</ref> The [[greater crested tern]] will also occasionally catch unusual [[vertebrate]] species such as [[Agamidae|agamid lizards]] and [[green sea turtle]] hatchlings, and follows trawlers for discards.<ref name= Blaber>{{cite journal| last= Blaber | first= S J M | author2=Milton, D A| author3=Smith, G C| author4=Farmer, M J |date=November 1995 | title= Trawl discards in the diets of tropical seabirds of the northern Great Barrier Reef, Australia | journal= Marine Ecology Progress Series | volume=127 | pages=1–13 | url = https://www.int-res.com/articles/meps/127/m127p001.pdf | doi = 10.3354/meps127001 | bibcode= 1995MEPS..127....1B | doi-access= free }}</ref>
The eyes of terns cannot [[Accommodation (eye)|accommodate]] under water, so they rely on accurate sighting from the air before they plunge-dive.<ref name= Coles/> Like other seabirds that feed at the surface or dive for food, terns have red oil droplets in the [[cone (eye)|cones]] of their [[retina]]s;<ref name= Sinclair/> birds that have to look through an air/water interface have more deeply coloured [[carotenoid]] [[pigment]]s in the oil drops than other species.<ref name = "Varela">Varela, F J; Palacios, A G; Goldsmith T M "Color vision in birds" in Ziegler & Bischof (1993) pp. 77–94.</ref> The pigment also improves visual contrast and sharpens distance vision, especially in hazy conditions,<ref name= Sinclair>Sinclair (1985) pp. 88–100.</ref> and helps terns to locate shoals of fish, although it is uncertain whether they are sighting the [[phytoplankton]] on which the fish feed, or other feeding birds.<ref name="Lythgoe">Lythgoe (1979) pp. 180–183.</ref> The red colouring reduces [[ultraviolet]] sensitivity, which in any case is an adaptation more suited to terrestrial feeders like the gulls,<ref name= Hastad>{{cite journal| last= Håstad | first= Olle | author2=Ernstdotter, Emma| author3=Ödeen, Anders | title= Ultraviolet vision and foraging in dip and plunge diving birds | journal= Biology Letters |volume=1 |issue=3 |pages=306–309|date=September 2005 |pmid= 17148194|doi= 10.1098/rsbl.2005.0320| pmc= 1617148}}</ref> and this protects the eye from UV damage.<ref name= Coles>Coles (2007) p. 30.</ref>
<gallery>
File:Sternula albifrons 2 - Little Swanport.jpg|[[Little tern]] in flight showing the forked tail
File:Gull-billed Tern, Parque Natural Río Lagartos, Yucatán, Mexico 1.jpg|The [[gull-billed tern]] will sometimes prey on the chicks and young of other terns
File:Chlidonias hybrida 2 (Marek Szczepanek).jpg|The [[whiskered tern]] is an insect-eating [[marsh tern]]
</gallery>
==Predators and parasites==
[[File:Western Gull chasing Elegant Tern.jpg|thumb|left|[[Kleptoparasitism|Kleptoparasitic]] [[western gull]] chasing an [[elegant tern]]]]
The inaccessibility of many tern colonies gave them a measure of protection from [[mammal]]ian predators, especially on islands, but [[introduced species]] brought by humans can seriously affect breeding birds. These can be predators such as [[fox]]es, [[raccoon]]s, [[cat]]s and [[rat]]s, or animals that destroy the habitat, including [[rabbit]]s, [[goat]]s and [[pig]]s.<ref name= HBW/> Problems arise not only on formerly mammal-free islands, as in New Zealand, but also where an alien [[carnivore]], such as the [[American mink]] in [[Scotland]], presents an unfamiliar threat.<ref name=hume112>Hume (1993) pp. 112–119.</ref>
Adult terns may be hunted by [[owl]]s and [[bird of prey|raptor]]s, and their chicks and eggs may be taken by [[heron]]s, [[crow]]s or gulls.<ref name= HBW/><ref name = qld/> Less obvious nest predators include [[ruddy turnstone]]s in the Arctic, and gull-billed terns in little tern colonies.<ref name = qld>{{cite web | title= Little tern | url= http://www.ehp.qld.gov.au/wildlife/animals-az/little_tern.html | publisher= Queensland Government Department of Environment and Heritage Protection | access-date= 13 May 2013 | archive-url= https://web.archive.org/web/20140310052535/http://www.ehp.qld.gov.au/wildlife/animals-az/little_tern.html | archive-date= 10 March 2014 | url-status= dead }}</ref><ref name=parkes>{{cite journal |last=Parkes |first=K C |author2=Poole, A |author3=Lapham, H  |year=1971 |title=The Ruddy Turnstone as an egg predator |journal=Wilson Bulletin |volume=83 |pages=306–307 |url=http://sora.unm.edu/sites/default/files/journals/wilson/v083n03/p0306-p0308.pdf}}</ref> Adults may be robbed of their catch by avian [[Kleptoparasitism|kleptoparasites]] such as [[frigatebird]]s, skuas, other terns or large gulls.<ref name= HBW/><ref name= harrison320>Harrison (1988) pp. 320–323.</ref>
External [[parasitism|parasite]]s include [[Mallophaga|chewing lice]] of the genus ''[[Saemundssonia]]'',<ref name= ward>{{cite journal |last= Ward |first= Ronald A |year=1955 |title= Biting lice of the genus ''Saemundssonia'' (Mallophaga: Philopteridae) occurring on terns| journal= Proceedings of the United States National Museum | volume= 105| pages=83–100 | url = https://www.biodiversitylibrary.org/page/15705141/#page/97/mode/1up |doi=10.5479/si.00963801.105-3353.83|issue=3353}}</ref> [[Bird louse|feather lice]] and fleas such as ''[[Ceratophyllus borealis]]''.<ref name = Rothschild82130>Rothschild & Clay (1953) p. 82, 130.</ref> Lice are often host specific, and the closely related common and Arctic terns carry quite different species.<ref name = Rothschild135>Rothschild & Clay (1953) p. 135.</ref> Internal parasites include the [[crustacean]] ''[[Reighardia sternae]]'', and [[cestoda|tapeworms]] such as ''[[Ligula intestinalis]]'' and members of the genera ''[[Diphyllobothrium]]'' and ''[[Schistocephalus]]''.<ref name = Rothschild194>Rothschild & Clay (1953) p. 194–197.</ref> Terns are normally free of blood parasites, unlike gulls that often carry ''[[Haemoproteus]]'' species. An exception is the brown noddy, which sometimes harbours [[protozoa]] of that genus.<ref name= Quillfeldt>{{cite journal |last= Quillfeldt |first= Petra | author2=Arriero, Elena| author3=Martínez, Javier| author4=Masello, Juan F| author5=Merino, Santiago |year= 2011|title= Prevalence of blood parasites in seabirds – a review | journal= Frontiers in Zoology | volume= 8 | pages=1–10 | url =http://www.frontiersinzoology.com/content/pdf/1742-9994-8-26.pdf | doi=10.1186/1742-9994-8-26|issue= 26 | pmid=22035144 | pmc=3223496 |doi-access= free }}</ref> In 1961 the common tern was the first wild bird species identified as being infected with avian influenza, the [[Influenza A virus subtype H5N3|H5N3]] variant being found in an outbreak involving South African birds.<ref name=olsen2006>{{cite journal |last=Olsen |first=Björn |author2=Munster, Vincent J |author3=Wallensten, Anders |author4=Waldenström, Jonas |author5=Osterhaus, D M E |author6= Fouchier, Ron A M  |year=2006 |title=Global patterns of influenza A virus in wild birds |journal=Science |volume=312 |issue=5772 |pages=384–388 |doi=10.1126/science.1122438 |pmid=16627734|bibcode=2006Sci...312..384O |s2cid=7795090 |doi-access= }}</ref> Several species of terns have been implicated as carriers of [[West Nile virus]].<ref name= Takken>Takken & Knols (2007) p. 137–140.</ref>
==Relationships with humans==
[[File:Roseate Tern portrait.jpg|thumb|The [[roseate tern]] is trapped for food on its wintering grounds.]]
Terns and their eggs have long been eaten by humans and island colonies were raided by sailors on long voyages since the eggs or large chicks were an easily obtained source of [[protein]]. Eggs are still illegally harvested in southern Europe, and adults of wintering birds are taken as food in West Africa and South America. The roseate tern is significantly affected by this hunting, with adult survival 10% lower than would otherwise be expected. In the West Indies, the eggs of roseate and sooty terns are believed to be [[aphrodisiac]]s, and are disproportionately targeted by egg collectors.{{citation needed|date=July 2024}} Tern skins and feathers have long been used for making items of clothing such as capes and hats, and this became a large-scale activity in the second half of the nineteenth century when it became fashionable to use feathers in [[hatmaking]]. This trend started in Europe but soon spread to the Americas and Australia. White was the preferred colour, and sometimes wings or entire birds were used.<ref name= HBW/><ref name=spenn>{{cite journal|last=Spennemann |first=Dirk H R |year=1999 |title=Exploitation of bird plumages in the German Mariana Islands |journal=Micronesica |volume=31 |pages=309–318 |url=http://www.uog.edu/up/micronesica/dynamicdata/assetmanager/images/vol31/spennemann.pdf |archive-url=https://web.archive.org/web/20100627061804/http://www.uog.edu/up/micronesica/dynamicdata/assetmanager/images/vol31/spennemann.pdf |archive-date=2010-06-27 |issue=2 |url-status=dead }}</ref>
Terns have sometimes benefited from human activities, following the plough or fishing boats for easy food supplies, although some birds get trapped in nets or swallow plastic. Fishermen looked for feeding tern flocks, since the birds could lead them to fish shoals. [[Overfishing]] of small fish such as [[sand eel]]s can lead to steep declines in the colonies relying on these prey items. More generally, the loss or disruption to tern colonies caused by human activities has caused declines in many species.<ref name= HBW/> Pollution has been a problem in some areas, and in the 1960s and 1970s [[DDT]] caused egg loss through thinning of the shells. In the 1980s, [[organochloride]]s caused severe declines in the [[Great Lakes]] area of the US.<ref name= burger/> Because of their sensitivity to pollutants, terns are sometimes used as indicators of contamination levels.<ref name= HBW/>
Habitat enhancements used to increase the breeding success of terns include floating nest platforms for black, common and Caspian terns,<ref name= shealer>{{cite journal |last= Shealer |first= D | author2=Buzzell, J| author3=Heiar, J |year=2006 |title= Effect of floating nest platforms on the breeding performance of black terns | journal= Journal of Field Ornithology | volume= 77 | pages=184–194 |doi=10.1111/j.1557-9263.2006.00040.x|issue=2|doi-access=free }}</ref><ref name= dunlop>{{cite journal |last= Dunlop |first=C L | author2=Blokpoel, H| author3=Jarvie, S |year=1991 |title= Nesting rafts as a management tool for a declining common tern (''Sterna hirundo'') colony | journal= Colonial Waterbirds | volume=14 | pages=116–120 |doi=10.2307/1521499|jstor= 1521499|issue=2}}</ref><ref name= lampman>{{cite journal |last= Lampman |first=K | author2=Taylor, M| author3=Blokpoel, H |year=1996 |title= Caspian terns (''Sterna caspia'') breed successfully on a nesting raft | journal= Colonial Waterbirds | volume=19 | pages=135–138 |doi=10.2307/1521819|jstor= 1521819|issue=1}}</ref> and artificial islands created for a number of different species.<ref name= burgess>{{cite journal |last= Burgess |first=N D |author2=Hirons, G J M  |year=1992 |title= Creation and management of artificial nesting sites for wetland birds | journal= Journal of Environmental Management | volume=34 | pages=285–295 |doi=10.1016/s0301-4797(11)80004-6|issue=4|bibcode=1992JEnvM..34..285B }}</ref><ref name= krogh>{{cite journal |last= Krogh |first= Michael G |author2=Schweitzer, Sara H  |year= 1999|title= Least terns nesting on natural and artificial habitats in Georgia, USA | journal= Waterbirds | volume= 22| pages=290–296 | url =http://obpa-nc.org/DOI-AdminRecord/0050143-0050149.pdf |doi=10.2307/1522218|jstor= 1522218|issue=2}}</ref> More specialised interventions include providing nest boxes for roseate terns, which normally nest in the shelter of tallish vegetation,<ref name= morrisson>{{cite journal |last= Morrison |first=P |author2=Gurney M  |year=2007 |title= Nest boxes for roseate terns ''Sterna dougallii ''on Coquet Island RSPB reserve, Northumberland, England | journal= Conservation Evidence | volume= 4| pages=1–3 }}</ref> and using artificial [[zostera|eelgrass]] mats to encourage common terns to nest in areas not vulnerable to flooding.<ref name=Palestis>{{cite journal |last=Palestis |first=Brian G |year=2009 |title=Use of artificial eelgrass mats by saltmarsh-nesting Common Terns (''Sterna hirundo'') |journal=In Vivo |volume=30 |issue=3 |pages=11–16 |url=http://aquaticcommons.org/4729/1/eelgrass_mats.pdf}}</ref>
==Conservation status==
[[File:Ranganathittu 3.jpg|thumb|left|The [[black-bellied tern]] is [[endangered species|endangered]] by human activities.]]
A number of terns face serious threats, and the [[Chinese crested tern]] is classed as "[[critically endangered]]" by [[BirdLife International]]. It has a population of fewer than 50&nbsp;birds and a breeding range of just {{convert|9|km2|sqmi|abbr=on}}. It is declining due to egg collection, human disturbance and the loss of coastal wetlands in China.<ref name = birdlifechinese>{{cite web| title= Chinese Crested Tern ''Sterna bernsteini'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3264 | publisher=BirdLife International | access-date =7 May 2013 }}</ref> Three other species are categorised as "[[Endangered species|endangered]]", with declining populations of less than 10,000 birds. The South Asian black-bellied tern is threatened by habitat loss, egg collecting for food, pollution and predation.<ref name = birdlifeacuticauda >{{cite web| title= Black-bellied Tern ''Sterna acuticauda'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3284 | publisher=BirdLife International | access-date =8 May 2013 }}</ref> In New Zealand, the black-fronted tern is facing a rapid fall in numbers due to predation by introduced mammals and [[Australian magpie]]s. Disturbance by cattle and sheep and by human activities is also a factor.<ref name = birdlifealbostriata>{{cite web| title= Black-fronted Tern ''Sterna albostriata'' | work= Species | url= http://www.birdlife.org/datazone/speciesfactsheet.php?id=3289| publisher=BirdLife International | access-date =8 May 2013 }}</ref> The Peruvian tern was initially damaged by the collapse of [[Peruvian anchoveta|anchoveta]] stocks in 1972, but breeding colonies have subsequently been lost due to building, disturbance and pollution in their coastal wetlands.<ref name = birdlifelorata>{{cite web| title= Peruvian Tern ''Sterna lorata'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3280 | publisher=BirdLife International | access-date =8 May 2013 }}</ref>
The [[Australasia]]n [[fairy tern]] is described as "[[Vulnerable species|vulnerable]]". Disturbance by humans, dogs and vehicles, predation by introduced species and inappropriate water level management in [[South Australia]] are the main reasons for its decline.<ref name = birdlifenereis >{{cite web| title= Fairy Tern ''Sterna nereis'' | work= Species | url= http://www.birdlife.org/datazone/speciesfactsheet.php?id=3281 | publisher=BirdLife International | access-date =8 May 2013 }}</ref> Five species are "[[near threatened]]", indicating less severe concerns or only potential vulnerability. The [[elegant tern]] is so categorised because 95% of the population breeds on one island, [[San Lorenzo Marine Archipelago National Park|Isla Rasa]] in the [[Gulf of California]], and the [[Kerguelen tern]] has a population of less than 5,000 adults breeding on small and often stormy islands in the southern [[Indian Ocean]].<ref name = birdlifevirgata >{{cite web| title= Kerguelen Tern ''Sterna virgata'' | work= Species | url= http://www.birdlife.org/datazone/speciesfactsheet.php?id=3273| publisher=BirdLife International | access-date =8 May 2013 }}</ref><ref name = birdlifeelegans>{{cite web| title= Elegant Tern ''Sterna elegans'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3261 | publisher=BirdLife International | access-date =8 May 2013 }}</ref> Three species, the Inca, Damara, and [[river tern]]s, are expected to decline in the future due to habitat loss and disturbance.<ref name = birdlifeinca>{{cite web| title= Inca Tern ''Larosterna inca'' | work= Species | url= http://www.birdlife.org/datazone/speciesfactsheet.php?id=3300| publisher=BirdLife International | access-date =8 May 2013 }}</ref><ref name = birdliferiver>{{cite web| title= River Tern ''Sterna aurantia'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3259 | publisher=BirdLife International | access-date =8 May 2013 }}</ref><ref name = birdlifedam>{{cite web| title= Damara Tern ''Sterna balaenarum'' | work= Species | url=http://www.birdlife.org/datazone/speciesfactsheet.php?id=3282 | publisher=BirdLife International | access-date =8 May 2013 }}</ref> Some tern [[subspecies]] are endangered, including the [[California least tern]] and the [[Easter Island]] race of the grey noddy.<ref name= HBW/>
Most tern species are declining in numbers due to the loss or disturbance of breeding habitat, pollution and increased predation. Gull populations have increased over the last century because of reduced persecution and the availability of food from human activities, and terns have been forced out of many traditional nesting areas by the larger birds. A few species are defying the trend and showing local increases, including the Arctic tern in [[Scandinavia]], Forster's tern around the Great Lakes, the [[Sandwich tern]] in eastern North America and its yellow-billed subspecies, the Cayenne tern, in the [[Caribbean]].<ref name= HBW/>
Terns are protected by international legislation such as the [[Agreement on the Conservation of African-Eurasian Migratory Waterbirds]] (AEWA) and the US-Canada [[Migratory Bird Treaty Act of 1918]].<ref name=AEWA>{{cite web|title=Annex 2: Waterbird species to which the Agreement applies |work=Agreement on the conservation of African-Eurasian migratory Waterbirds (AEWA) |url=http://www.unep-aewa.org/documents/agreement_text/eng/pdf/aewa_agreement_text_annex2.pdf |archive-url=https://web.archive.org/web/20110728144028/http://www.unep-aewa.org/documents/agreement_text/eng/pdf/aewa_agreement_text_annex2.pdf |archive-date=28 July 2011 |publisher=UNEP/ AEWA Secretariat |access-date=25 January 2012 |url-status=dead }}</ref><ref name=1918treaty>{{cite web |title=List of Migratory Birds |work=Birds protected by the Migratory Bird Treaty Act |url=http://www.fws.gov/migratorybirds/RegulationsPolicies/mbta/mbtandx.html |publisher=US Fish and Wildlife Service|access-date=25 January 2012}}</ref> Parties to the AWEA 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.<ref name=AEWAintro>{{cite web |title=Introduction |work=African-Eurasian Waterbird Agreement |url=http://www.unep-aewa.org/about/introduction.htm |archive-url=https://web.archive.org/web/20120211082252/http://www.unep-aewa.org/about/introduction.htm |archive-date=2012-02-11 |publisher=UNEP/ AEWA Secretariat |access-date=25 January 2012}}</ref> The North American legislation is similar, although there is a greater emphasis on protection.<ref name=law>{{cite web |title=Migratory Bird Treaty Act of 1918 |work=Digest of Federal Resource Laws of Interest to the U. S. Fish and Wildlife Service |url=http://www.fws.gov/laws/lawsdigest/migtrea.html |publisher=U. S. Fish and Wildlife Service|access-date=25 January 2012}}</ref>
==See also==
* [[Seabird breeding behavior]]
==References==
{{Reflist|30em}}
===Cited texts===
{{div col|content=
* {{cite book |title=A Field Guide to Birds of The Gambia and Senegal|last= Barlow |first=Clive | author2=Wacher, Tim| author3=Disley, Tony |publisher=Pica Press|year=1997 |isbn= 1-873403-32-1|location= Robertsbridge }}
* {{cite book |last=Burton |first=Robert |title=Bird Behaviour |year=1985 |publisher=Granada Publishing |location=London |isbn=0-246-12440-7 |url-access=registration |url=https://archive.org/details/birdbehaviour0000burt }}
* {{cite book | last = Constantine | first = Mark |author2=The Sound Approach  | title = The Sound Approach to birding: a guide to understanding bird sound | publisher = The Sound Approach | location = Poole | year = 2006 | isbn = 90-810933-1-2}}
* {{cite book | last= Coles | first= Brian | year=2007 | title= Essentials of Avian Medicine and Surgery |publisher = Wiley | location = Oxford| isbn =978-1-4051-5755-1 }}
* {{cite book | author1=Gochfeld, M. |author2=Burger, J. |chapter=Family Sternidae (Terns) |pages=624–667 |editor-last1=del Hoyo | editor-first1= Josep | editor-last2= Elliott |editor-first2=Andrew | editor-last3= Sargatal |editor-first3=Jordi | year= 1996 | title= Handbook of Birds of the World | volume= 3: Hoatzin to Auks | url= https://archive.org/details/handbookofbirdso0001unse | publisher= Lynx Edicions | location= Barcelona | isbn= 978-84-87334-20-7 | url-access= registration }}
* {{cite book | last= Harrison | first= Peter | year=1988 | title= Seabirds: An Identification Guide |publisher = Christopher Helm | location = London| isbn = 0-7470-1410-8 }}
* {{cite book | last = Hume | first = Rob | title = The Common Tern | year = 1993 | location = London | publisher = Hamlyn | isbn = 0-540-01266-1}}
* {{cite book | last = Hume | first = Rob |author2=Pearson, Bruce  | title = Seabirds | year = 1993 | location = London | publisher = Hamlyn | isbn = 0-600-57951-4}}
* {{cite book | last= Hutton | first= Frederick Wollaston |author2=Drummond, James  | year=2011 |edition=reprint |orig-year=1904 | title= The animals of New Zealand: an account of the dominion's air-breathing vertebrates |publisher = Cambridge University Press | location = Cambridge | isbn = 978-1-108-04002-0 }}
* {{cite book | last= Jobling | first= James A | year= 2010| title= The Helm Dictionary of Scientific Bird Names | url =http://nature.baikal.ru/files/605/1408125013.pdf |publisher = Christopher Helm | location = London | isbn = 978-1-4081-2501-4 }}
* {{cite book | last=Linnaeus | first=C | author-link=Carl Linnaeus | title=Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. | publisher=Laurentii Salvii| location = Holmiae [Stockholm] | year=1758|language =la}}
* {{cite book | last = Lockwood| first =W B | title = Oxford Book of British Bird Names | year = 1984 | publisher = [[Oxford University Press]] | location= Oxford | isbn = 0-19-214155-4 }}
* {{cite book|last=Lythgoe |first=J N|title=The Ecology of Vision |year=1979 |location=Oxford|publisher=Clarendon Press |isbn=0-19-854529-0 }}
* {{cite book | last= Maehr | first= David S |author2=Kale, Herbert W  | year=2005 | title= Florida's Birds |publisher = Pineapple Press | location = Sarasota | isbn = 1-56164-335-1 }}
* {{cite web | last = Merriam-Webster | year = 2014 | title = Tern - Definition and More from the Free Merriam-Webster Dictionary | publisher = Encyclopædia Britannica | url = http://www.merriam-webster.com/dictionary/tern | access-date = January 11, 2014}}
* {{cite book | last = Newton | first = Ian | title = Bird Migration (Collins New Naturalist Library 113) | year = 2010 | location = London | publisher = Collins | isbn = 978-0-00-730732-6 }}
* {{cite book| last = Olsen | first = Klaus Malling |author2=Larsson, Hans  | title = Terns of Europe and North America | year =1995 | publisher = Christopher Helm |location = London| isbn =0-7136-4056-1}}
* {{cite book | last= Perrins | first= Christopher M |author2=Arlott, Norman  | year= 1987| title= New generation guide to the birds of Britain and Europe |publisher = University of Texas Press | location = Austin | isbn = 0-292-75532-5}}
* {{cite book |title= Fleas, Flukes and Cuckoos. A study of bird parasites |author1= [[Miriam Rothschild|Rothschild, Miriam]] |author2=[[Theresa Clay|Clay, Theresa]] |year= 1953 |publisher= Collins |location= London |url= https://archive.org/details/fleasflukescucko017900mbp }}
* {{cite book|last=Sinclair |first=Sandra | title = How Animals See: Other Visions of Our World |year= 1985|publisher=Croom Helm |location=Beckenham, London |isbn=0-7099-3336-3 }}
* {{cite book | editor-last= Steele | editor-first= John H | editor2= Thorpe Steve A | editor3= Turekian, Karl K | year= 2001 | title= Encyclopedia of Ocean Sciences | url= https://archive.org/details/encyclopediaofoc0000unse | publisher= Academic Press | location= London | isbn= 978-0-12-227430-5 | url-access= registration }}
* {{cite book | last = Svensson | first = Lars | author2=Mullarney, Killian| author3=Zetterstrom, Dan| author4=Grant, Peter |title = Collins Bird Guide | year = 1999 | publisher = Collins |location = London |isbn = 0-00-219728-6}}
* {{cite book | editor-last= Takken | editor-first= Willem | editor2=Knols, Bart G J | year=2007 | title= Emerging pests and vector-borne diseases in Europe |publisher = Wageningen Academic Publishers | location = Wageningen | isbn = 978-90-8686-053-1 }}
* {{cite book | last = Turner | first = William | author-link = William Turner (naturalist) | title = Turner on Birds (Auium præcipuarum, quarum apud Plinium et Aristotelem mentio est, breuis et succincta historia) | editor = Evans, A H | edition = 1903 | publisher = Cambridge University Press | location = Cambridge | quote = ''huius generis est & alia parua auis, nostrati lingua sterna apellata'' 'There is another small bird of this type, called Stern in local dialect' | url = https://archive.org/stream/turneronbirds00turnrich#page/78/mode/2up | access-date = January 11, 2014}}
* {{cite book | last = Watling | first = Dick | author-link=Dick Watling|title = A Guide to the Birds of Fiji and Western Polynesia | year = 2003 | location = Suva, Fiji | publisher = Environmental Con-sultants | isbn =982-9030-04-0}}
* {{cite book|editor-last=Ziegler |editor-first=Harris Philip | editor2=Bischof, Hans-Joachim |title=Vision, Brain, and Behavior in Birds: A comparative review |year=1993 |publisher=MIT Press|isbn=0-262-24036-X |location = Cambridge }}
}}
== External links==
{{Commons category|Sternidae}}
{{Wiktionary}}
*[http://ibc.lynxeds.com/family/terns-sternidae Tern videos] on the Internet Bird Collection
{{portalbar|Birds|Animals|Biology}}
{{Taxonbar|from=Q875769}}
{{Authority control}}
[[Category:Terns| ]]
[[Category:Extant Miocene first appearances]]
[[Category:Laridae|*]]
[[Category:Taxa named by Charles Lucien Bonaparte]]