Editing Common tern (section)

==Behaviour==
===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/>

===Breeding===
[[File:Common tern (Sterna hirundo) fledgling Danube delta.jpg|thumb|Fledgling, Danube delta, Romania]]
Pairs are established or confirmed through aerial [[courtship display]]s in which a male and a female fly in wide circles up to {{convert|200|m|abbr=on}} or more, calling all the while, before the two birds descend together in zigzag glides. If the male is carrying a fish, he may attract the attention of other males too. On the ground, the male courts the female by circling her with his tail and neck raised, head pointing down, and wings partially open. If she responds, they may both adopt a posture with the head pointed skywards. The male may tease a female with the fish, not parting with his offering until she has displayed to him sufficiently.<ref name=hume91>Hume (1993) pp. 91–99.</ref> Once courtship is complete, the male makes a shallow depression in the sand, and the female scratches in the same place. Several trials may take place until the pair settle on a site for the actual nest.<ref name=hume91/> The eggs may be laid on bare sand, gravel or soil, but a lining of debris or vegetation is often added if available,<ref name=snow779/> or the nest may be rimmed with seaweed, stones or shells. The saucer-shaped scrape is typically {{convert|4|cm|abbr=on}} deep and {{convert|10|cm|abbr=on}} across, but may extend to as much as {{convert|24|cm|abbr=on}} wide including the surrounding decorative material.<ref name=hume100>Hume (1993) pp. 100–111.</ref> Breeding success in areas prone to flooding has been enhanced by the provision of artificial mats made from [[Zostera|eelgrass]], which encourage the terns to nest in higher, less vulnerable areas, since many prefer the mats to bare sand.<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 |access-date=8 February 2012 |archive-date=27 May 2014 |archive-url=https://web.archive.org/web/20140527215847/http://aquaticcommons.org/4729/1/eelgrass_mats.pdf |url-status=live }}</ref> The common tern tends to use more nest material than roseate or Arctic terns, although roseate often nests in areas with more growing vegetation.<ref name= Lloyd>Lloyd et al. (2010) p. 207.</ref><ref name= Bent>Bent (1921) p. 252.</ref>

Terns are expert at locating their nests in a large colony. Studies show that terns can find and excavate their eggs when they are buried, even if the nest material is removed and the sand smoothed over. They will find a nest placed {{convert|5|m|abbr=on}} from its original site, or even further if it is moved in several stages. Eggs are accepted if reshaped with [[plasticine]] or coloured yellow (but not red or blue). This ability to locate the eggs is an adaptation to life in an unstable, wind-blown and tidal environment.<ref name= Fisher/>

The peak time for egg production is early May, with some birds, particularly first-time breeders, laying later in the month or in June.<ref name=ontario/><ref name=hume100/> The [[Clutch (eggs)|clutch]] size is normally three eggs; larger clutches probably result from two females laying in the same nest. Egg size averages {{convert|41|x|31|mm|abbr=on}}, although each successive egg in a clutch is slightly smaller than the first laid.<ref name=hume100/> The average egg weight is {{convert|20.2|g|abbr=on}}, of which five per cent is shell.<ref name=bto>{{cite web |title=Common Tern ''Sterna hirundo'' (Linnaeus, 1758) |work=BirdFacts |date=16 July 2010 |url=http://blx1.bto.org/birdfacts/results/bob6150.htm |publisher=British Trust for Ornithology (BTO) |access-date=9 February 2012 |archive-date=18 January 2012 |archive-url=https://web.archive.org/web/20120118042434/http://blx1.bto.org/birdfacts/results/bob6150.htm |url-status=live }}</ref> The egg weight depends on how well-fed the female is, as well as on its position in the clutch. The eggs are cream, [[Buff (colour)|buff]], or pale brown, marked with streaks, spots or blotches of black, brown or grey which help to camouflage them.<ref name=hume100/> Incubation is by both sexes, although more often by the female, and lasts 21–22 days,<ref name=bto/> extending to 25{{nbs}}days if there are frequent disturbances at the colony which cause the adults to leave the eggs unattended;<ref name=hume100/> nocturnal predation may lead to incubation taking up to 34{{nbs}}days.<ref name=ontario/> On hot days the incubating parent may fly to water to wet its belly feathers before returning to the eggs, thus affording the eggs some cooling.<ref name=nisbet/> Except when the colony suffers disaster, ninety per cent of the eggs hatch.<ref name=hume112/> The [[precocial]] [[down feather|downy]] chick is yellowish with black or brown markings,<ref name=hume100/> and like the eggs, is similar to the equivalent stage of the Arctic tern.<ref name=pearson121>Hume & Pearson (1993) pp. 121–124.</ref> The chicks [[fledge]] in 22–28 days,<ref name=bto/> usually 25–26.<ref name=snow779/> Fledged juveniles are fed at the nest for about five days, and then accompany the adults on fishing expeditions. The young birds may receive supplementary feeds from the parents until the end of the breeding season, and beyond. Common terns have been recorded feeding their offspring on migration and in the wintering grounds, at least until the adults move further south in about December.<ref name=nisbet/><ref name=hume120>Hume (1993) pp. 120–123.</ref>

Like many terns, this species is very defensive of its nest and young, and will harass humans, dogs, [[muskrat]]s and most [[Diurnality|diurnal]] birds, but unlike the more aggressive Arctic tern, it rarely hits the intruder, usually swerving off at the last moment. Adults can discriminate between individual humans, attacking familiar people more intensely than strangers.<ref name= Burger>{{cite journal |last=Burger |first=Joanna |author2=Shealer, D A |author3=Gochfeld, Michael |year=1993 |title=Defensive aggression in terns: discrimination and response to individual researchers |journal=Aggressive Behavior |volume=19 |issue=4 |pages=303–311 |doi=10.1002/1098-2337(1993)19:4<303::AID-AB2480190406>3.0.CO;2-P}}</ref> Nocturnal predators do not elicit similar attacks;<ref name= hunter>{{cite journal |last=Hunter |first=Rodger A |author2=Morris, Ralph D |year=1976 |title=Nocturnal predation by a Black-Crowned Night Heron at a Common Tern colony |journal=Auk |url=http://sora.unm.edu/node/22862 |volume=93 |issue=3 |pages=629–633 |jstor=4084965 |access-date=22 February 2013 |archive-date=28 May 2014 |archive-url=https://web.archive.org/web/20140528012956/https://sora.unm.edu/node/22862 |url-status=live }}</ref> colonies can be wiped out by rats, and adults desert the colony for up to eight hours when [[great horned owl]]s are present.<ref name= nisbet3>{{cite journal |last=Nisbet |first=Ian C T |author2=Welton, M |year=1984 |title=Seasonal variations in breeding success of Common Terns: consequences of predation |journal=Condor |volume=86 |issue=1 |pages=53–60 |url=http://sora.unm.edu/node/103417 |jstor=1367345 |doi=10.2307/1367345 |access-date=22 February 2013 |archive-date=28 May 2014 |archive-url=https://web.archive.org/web/20140528020412/https://sora.unm.edu/node/103417 |url-status=live |url-access=subscription }}</ref>

Common terns usually breed once a year. Second clutches are possible if the first is lost. Rarely, a second clutch may be laid and incubated while some chicks from the first clutch are still being fed.<ref name= hays>{{cite journal |last=Hays |first=H |year=1984 |title=Common Terns raise young from successive broods |journal=Auk |volume=101 |issue=2 |pages=274–280 |url=http://sora.unm.edu/sites/default/files/journals/auk/v101n02/p0274-p0280.pdf |doi=10.1093/auk/101.2.274 |access-date=22 February 2013 |archive-date=18 July 2015 |archive-url=https://web.archive.org/web/20150718134846/http://sora.unm.edu/sites/default/files/journals/auk/v101n02/p0274-p0280.pdf |url-status=live }}</ref> The first breeding attempt is usually at four years of age, sometimes at three years. The average number of young per pair surviving to fledging can vary from zero in the event of the colony being flooded to over 2.5 in a good year. In North America, productivity was between 1.0 and 2.0 on islands, but less than 1.0 at coastal and inland sites. Birds become more successful at raising chicks with age. This continues throughout their breeding lives, but the biggest increase is in the first five years.<ref name=nisbet/><ref name="pearson121"/> The maximum documented lifespan in the wild is 23{{nbs}}years in North America<ref name=nisbet2>{{cite journal |last=Nisbet |first=Ian C T |author2=Cam, Emmanuelle |year=2002 |title=Test for age-specificity in survival of the Common Tern |journal=Journal of Applied Statistics |volume=29 |issue=1–4 |pages=65–83 |doi=10.1080/02664760120108467|bibcode=2002JApSt..29...65N |s2cid=62816201 }}</ref><ref name=austin2>{{cite journal |last=Austin |first=Oliver L Sr |year=1953 |title=A Common Tern at least 23 years old |journal=Bird-Banding |volume=24 |issue=1 |page=20 |url=http://sora.unm.edu/sites/default/files/journals/jfo/v024n01/p0020-p0020.pdf |access-date=22 February 2013 |archive-date=1 March 2014 |archive-url=https://web.archive.org/web/20140301131214/http://sora.unm.edu/sites/default/files/journals/jfo/v024n01/p0020-p0020.pdf |url-status=live }}</ref> and 33{{nbs}}years in Europe,<ref name=agebi>{{cite web |title=Longevity records for Britain & Ireland in 2010 |work=Online ringing report |url=http://blx1.bto.org/ring/countyrec/results2010/longevity.htm |publisher=British Trust for Ornithology (BTO) |archive-url=https://web.archive.org/web/20120228140407/http://blx1.bto.org/ring/countyrec/results2010/longevity.htm |archive-date=28 February 2012|access-date=11 February 2012}}</ref><ref name=ageeu>{{cite web |title=European Longevity Records |work=Longevity |url=http://www.euring.org/data_and_codes/longevity-voous.htm |publisher=Euring |access-date=11 February 2012 |archive-date=11 May 2015 |archive-url=https://web.archive.org/web/20150511193839/http://www.euring.org/data_and_codes/longevity-voous.htm |url-status=live }}</ref> but twelve years is a more typical lifespan.<ref name=bto/>

<gallery widths="200px" heights="165px">
File:Common Terns nesting.jpg|Nest site, [[Elliston, Newfoundland and Labrador]]
File:Batalla de golondrinas de mar (Sterna hirundo).jpg|Nest in the [[Ebro Delta]], Tarragona, Catalonia, Spain
File:Sterna hirundo MWNH 0472.JPG|Egg, Collection [[Museum Wiesbaden]]
File:Sterna hirundo -nest with three eggs-8.jpg|Three eggs in a nest on [[Great Gull Island]]
File:CommonTern-Chick.jpg|A chick on an island off the coast of Maine
File:Sterna hirundo -hovering to protect nest-8.jpg|Hovering and screaming to deter intruders on [[Great Gull Island]]
File:Sterna hirundo -Massachusetts, USA -juvenile-8.jpg|This autumn juvenile in Massachusetts has a white forehead, having lost the ginger colouration characteristic of younger birds.
</gallery>

===Food and feeding===
[[File:Sterna hirundo -West Bromwich, England -flying-8.jpg|thumb|Flying over a pond in England. The head and bill point down during a search for fish.]]

Like all ''Sterna'' terns, the common tern feeds by plunge-diving for fish, from a height of {{convert|1|-|6|m|ft|abbr=on}}, either in the sea or in freshwater lakes and large rivers. The bird may submerge for a second or so, but to no more than {{convert|50|cm|abbr=on}} below the surface.<ref name=hume55>Hume (1993) pp. 55–67.</ref> When seeking fish, this tern flies head-down and with its bill held vertically.<ref name=Fisher>Fisher & Lockley (1989) pp. 252–260.</ref> It may circle or hover before diving, and then plunges directly into the water, whereas the Arctic tern favours a "stepped-hover" technique,<ref>Beaman et al. (1998) p. 440.</ref> and the roseate tern dives at speed from a greater height, and submerges for longer.<ref name=BB80>{{cite journal |last=Kirkham |first=Ian R |author2=Nisbet, Ian C T |year=1987 |title=Feeding techniques and field identification of Arctic, Common and Roseate Terns |journal=British Birds |volume=80 |issue=2 |pages=41–47}}</ref> The common tern typically forages up to {{convert|5|-|10|km|mi|abbr=on}} away from the breeding colony, sometimes as far as {{convert|15|km|abbr=on}}.<ref name = BirdLife>{{cite web | title = BirdLife International Species factsheet: ''Sterna hirundo'' | publisher = BirdLife International | url = http://www.birdlife.org/datazone/speciesfactsheet.php?id=3270 | access-date = 23 January 2012 | archive-date = 15 October 2016 | archive-url = https://web.archive.org/web/20161015233814/http://www.birdlife.org/datazone/speciesfactsheet.php?id=3270 | url-status = live }}</ref> It will follow schools of fish, and its west African migration route is affected by the location of huge shoals of [[sardine]]s off the coast of Ghana;<ref name=hume55/> it will also track groups of [[predatory fish]] or [[dolphin]]s, waiting for their prey to be driven to the sea's surface.<ref name = BirdLife/><ref name=bugoni>{{cite journal |last=Bugoni |first=Leandro |author2=Vooren, Carolus Maria |year=2004 |title=Feeding ecology of the Common Tern ''Sterna hirundo'' in a wintering area in southern Brazil |journal=Ibis |volume=146 |issue=3 |pages=438–453 |doi=10.1111/j.1474-919X.2004.00277.x}}</ref> Terns often feed in flocks, especially if food is plentiful, and the fishing success rate in a flock is typically about one-third higher than for individuals.<ref name=hume55/>

Terns have red oil droplets in the [[cone cell]]s of the [[retina]]s of their eyes. This improves contrast and sharpens distance [[Bird vision|vision]], especially in hazy conditions.<ref name=Sinclair>Sinclair (1985) pp. 93–95.</ref> Birds that have to see through an air/water interface, such as terns and gulls, have more strongly coloured [[carotenoid]] [[pigment]]s in the cone oil drops than other avian species.<ref name=Varela>Varela, F J; Palacios, A G; Goldsmith T M (1993) "Vision, Brain, and Behavior in Birds" in Zeigler & Bischof (1993) pp. 77–94.</ref> The improved eyesight helps terns to locate shoals of fish, although it is uncertain whether they are sighting the [[phytoplankton]] on which the fish feed, or observing other terns diving for food.<ref name=Lythgoe>Lythgoe (1979) pp. 180–183.</ref> Tern's eyes are not particularly [[ultraviolet]] sensitive, 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 |year=2005 |pmid=17148194 |doi=10.1098/rsbl.2005.0320 |pmc=1617148}}</ref>
[[File:Sterna hirundo -Nantucket National Wildlife Refuge, Massachusetts, USA -adult and juvenile-8.jpg|thumb|An adult bringing a [[sand eel]] to a juvenile at [[Nantucket National Wildlife Refuge]]]]

The common tern preferentially hunts fish {{convert|5|-|15|cm|in|abbr=on}} long.<ref name=ontario>Sandilands (2005) pp. 157–160.</ref><ref name=hume55/> The species caught depend on what is available, but if there is a choice, terns feeding several chicks will take larger prey than those with smaller broods.<ref name= Stephens>Stephens et al. (2007) p. 295.</ref> The proportion of fish fed to chicks may be as high as ninety-five per cent in some areas, but [[invertebrate]] prey may form a significant part of the diet elsewhere. This may include [[Annelid|worm]]s, [[leech]]es, [[Mollusca|mollusc]]s such as small [[squid]], and [[crustacean]]s ([[prawn]]s, [[shrimp]] and [[Hippoidea|mole crabs]]). In freshwater areas, large [[insect]]s may be caught, such as [[beetle]]s, [[cockchafer]]s and [[moth]]s. Adult insects may be caught in the air, and [[larva]]e picked from the ground or from the water surface. Prey is caught in the bill and either swallowed head-first, or carried back to the chicks. Occasionally, two or more small fish may be carried simultaneously.<ref name=hume55/> When adults take food back to the nest, they recognise their young by call, rather than visual identification.<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>

The common tern may attempt to steal fish from Arctic terns,<ref name=hopkins>{{cite journal |last=Hopkins |first=C D |author2=Wiley, R H |year=1972 |title=Food parasitism and competition in two terns |journal=Auk |volume=89 |pages=583–594 |url=http://sora.unm.edu/sites/default/files/journals/auk/v089n03/p0583-p0594.pdf |access-date=22 February 2013 |archive-date=21 April 2014 |archive-url=https://web.archive.org/web/20140421102806/http://sora.unm.edu/sites/default/files/journals/auk/v089n03/p0583-p0594.pdf |url-status=live }}</ref> but might itself be harassed by [[kleptoparasitism|kleptoparasitic]] skuas,<ref name=belisle>{{cite journal |last=Bélisle |first=M |year=1998 |title=Foraging group size: models and a test with jaegers kleptoparasitizing terns |journal=Ecology |volume=79 |issue=6 |pages=1922–1938 |url=http://spectrum.library.concordia.ca/6255/1/MM18374.pdf |doi=10.2307/176699 |jstor=176699 |bibcode=1998Ecol...79.1922B |access-date=16 March 2012 |archive-date=21 April 2014 |archive-url=https://web.archive.org/web/20140421050645/http://spectrum.library.concordia.ca/6255/1/MM18374.pdf |url-status=live }}</ref> [[laughing gull]]s,<ref name=hatch>{{cite journal |last=Hatch |first=J J |year=1975 |title=Piracy by laughing gulls ''Larus atricilla'': an example of the selfish group |journal=Ibis |volume=117 |issue=3 |pages=357–365 |doi=10.1111/j.1474-919X.1975.tb04222.x}}</ref> roseate terns,<ref name=dunn>{{cite journal |last=Dunn |first=E K |year=1973 |title=Robbing behavior of Roseate Terns |journal=Auk |url=http://sora.unm.edu/node/22405 |volume=90 |pages=641–651 |jstor=4084163 |doi=10.2307/4084163 |issue=3 |access-date=22 February 2013 |archive-date=21 April 2014 |archive-url=https://web.archive.org/web/20140421151548/https://sora.unm.edu/node/22405 |url-status=live |doi-access=free |url-access=subscription }}</ref> or by other common terns while bringing fish back to its nest.<ref name=hopkins/> In one study, two males whose mates had died spent much time stealing food from neighbouring broods.<ref name=wilson>{{cite journal |last=Nisbet |first=Ian C T |author2=Wilson, Karen J |author3=Broad, William A |year=1978 |title=Common Terns raise young after death of their mates |journal=The Condor |url=http://sora.unm.edu/node/102828 |volume=80 |issue=1 |pages=106–109 |doi=10.2307/1367802 |jstor=1367802 |access-date=22 February 2013 |archive-date=21 April 2014 |archive-url=https://web.archive.org/web/20140421132515/https://sora.unm.edu/node/102828 |url-status=live |url-access=subscription }}</ref>

Terns normally drink in flight, usually taking seawater in preference to freshwater, if both are available.<ref name=nisbet/> Chicks do not drink before fledging, reabsorbing water, and, like adults, excreting excess salt in a concentrated solution from a specialised nasal gland.<ref name= hughes>{{cite journal |last=Hughes |first=M R |year=1968 |title=Renal and extrarenal sodium excretion in the Common Tern ''Sterna hirundo'' |journal=Physiological Zoology |volume=41 |issue=2 |pages=210–219 |jstor=30155452|doi=10.1086/physzool.41.2.30155452|s2cid=87163637 }}</ref><ref name=Karleskint>Karleskint (2009) p. 317.</ref> Fish bones and the hard [[exoskeleton]]s of crustaceans or insects are regurgitated as [[pellet (ornithology)|pellets]]. Adults fly off the nest to [[Defecation|defecate]], and even small chicks walk a short distance from the scrape to deposit their [[Feces|faeces]]. Adults attacking animals (including humans) will often defecate as they dive, often successfully fouling the intruder.<ref name=nisbet/>