Editing Common tern (section)

===Territory===
The common tern breeds in colonies which do not normally exceed two thousand [[Breeding pair|pair]]s,<ref name= snow779/> but may occasionally number more than twenty thousand pairs.<ref name= wolf>de Wolf, P. "BioIndicators and the Quality of the Wadden Sea" in Best & Haeck (1984) p. 362.</ref> Colonies inland tend to be smaller than on the coast. Common terns often nest alongside other coastal species, such as Arctic,<ref name=rob>{{cite journal |last=Robinson |first=James A |author2=Chivers, Lorraine S |author3=Hamer, Keith C |year=2001 |title=A comparison of Arctic Tern ''Sterna paradisaea'' and Common Tern ''S. hirundo'' nest-site characteristics on Coquet Island, north-east England |journal=Atlantic Seabirds |volume=3 |issue=2 |pages=49–58 |url=http://www.seabirdgroup.org.uk/journals/as_3_2.pdf |archive-url=https://web.archive.org/web/20140527212407/http://www.seabirdgroup.org.uk/journals/as_3_2.pdf |archive-date=27 May 2014}}</ref> roseate and [[Sandwich tern]]s, [[black-headed gull]]s,<ref name=ramos>{{cite journal |last=Ramos |first=Jaime A |author2=Adrian J |year=1995 |title=Nest-site selection by Roseate Terns and Common Terns in the Azores |journal=Auk |volume=112 |issue=3 |pages=580–589 |url=http://sora.unm.edu/sites/default/files/journals/auk/v112n03/p0580-p0589.pdf |access-date=22 February 2013 |archive-date=28 May 2014 |archive-url=https://web.archive.org/web/20140528005645/http://sora.unm.edu/sites/default/files/journals/auk/v112n03/p0580-p0589.pdf |url-status=live }}</ref><ref name=fuchs>{{cite journal |last=Fuchs |first=Eduard |year=1977 |title=Predation and anti-predator behaviour in a mixed colony of terns ''Sterna'' sp. and Black-Headed Gulls ''Larus ridibundus'' with special reference to the Sandwich Tern ''Sterna sandvicensis'' |journal=Ornis Scandinavica |volume=8 |issue=1 |pages=17–32 |doi=10.2307/3675984|jstor=3675984}}</ref> and [[black skimmer]]s.<ref name=erwin>{{cite journal |last=Erwin |first=Michael R |year=1977 |title=Black Skimmer breeding ecology and behavior |journal=Auk |volume=94 |pages=709–717 |url=http://sora.unm.edu/sites/default/files/journals/auk/v094n04/p0709-p0717.pdf |doi=10.2307/4085267 |issue=4 |jstor=4085267 |access-date=22 February 2013 |archive-date=27 May 2014 |archive-url=https://web.archive.org/web/20140527214231/http://sora.unm.edu/sites/default/files/journals/auk/v094n04/p0709-p0717.pdf |url-status=live }}</ref> Especially in the early part of the breeding season, for no known reason, most or all of the terns will fly in silence low and fast out to sea. This phenomenon is called a "dread".<ref name= snow779/>

On their return to the breeding sites, the terns may loiter for a few days before settling into a territory,<ref name=hume86/> and the actual start of nesting may be linked to a high availability of fish.<ref name=safina>{{cite journal |last=Safina |first=Carl |author2=Burger, Joanna |year=1988 |title=Prey dynamics and the breeding phenology of Common Terns (''Sterna hirundo'') |journal=Auk |volume=105 |issue=4 |pages=720–726 |url=http://sora.unm.edu/sites/default/files/journals/auk/v105n04/p0720-p0726.pdf |doi=10.1093/auk/105.4.720 |access-date=22 February 2013 |archive-date=18 July 2015 |archive-url=https://web.archive.org/web/20150718134823/http://sora.unm.edu/sites/default/files/journals/auk/v105n04/p0720-p0726.pdf |url-status=live }}</ref> Terns defend only a small area, with distances between nests sometimes being as little as {{convert|50|cm|abbr=on}}, although {{convert|150|-|350|cm|abbr=on}} is more typical. As with many birds, the same site is re-used year after year, with a record of one pair returning for 17 successive breeding seasons. Around ninety per cent of experienced birds reuse their former territory, so young birds must nest on the periphery, find a bereaved mate, or move to another colony.<ref name=hume86>Hume (1993) pp. 86–90.</ref> A male selects a nesting territory a few days after his arrival in the spring, and is joined by his previous partner unless she is more than five days late, in which case the pair may separate.<ref name=solis>{{cite journal |last=Gonzalez-Solis |first= J |author2=Becker, P H |author3=Wendeln, H |s2cid= 24145857 |year=1999 |title=Divorce and asynchronous arrival in Common Terns (''Sterna hirundo'') |journal=Animal Behaviour |volume=58 |issue=5 |pages=1123–1129 |doi=10.1006/anbe.1999.1235 |pmid=10564616}}</ref>

Inbreeding among close ''S. hirundo'' relatives appears to be avoided passively by immigration and dispersal rather than by [[kin recognition|kin discrimination]] and [[mate choice]].<ref>Sonja C. Ludwig, Peter H. Becker (2011) Immigration prevents inbreeding in a growing colony of a long-lived and philopatric seabird. Ibis. volume 154, Issue 1, pgs. 74–84. https://doi.org/10.1111/j.1474-919X.2011.01199.x</ref>

The defence of the territory is mainly by the male, who repels intruders of either sex. He gives an alarm call, opens his wings, raises his tail and bows his head to show the black cap. If the intruder persists, the male stops calling and fights by bill grappling until the intruder submits by raising its head to expose the throat. Aerial trespassers are simply attacked, sometimes following a joint upward spiralling flight.<ref name=hume86/> Despite the aggression shown to adults, wandering chicks are usually tolerated, whereas in a gull colony they would be attacked and killed. The nest is defended until the chicks have fledged, and all the adults in the colony will collectively repel potential predators.<ref name=hume79/>