Editing Tern (section)

==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>