Editing Common tern (section)

===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/>