Editing Bird (section)

===Diet and feeding===
{{see also|Bird food}}
[[File:BirdBeaksA.svg|thumb|upright|right|alt= Illustration of the heads of 16 types of birds with different shapes and sizes of beak|Feeding adaptations in beaks]]
{{Birdgloss|dietary classification terms (-vores)|Birds' diets}} are varied and often include [[nectar (plant)|nectar]], fruit, plants, seeds, [[carrion]], and various small animals, including other birds.<ref name="Gill"/> The [[digestive system of birds]] is unique, with a [[Crop (anatomy)|crop]] for storage and a [[gizzard]] that contains swallowed stones for grinding food to compensate for the lack of teeth.<ref>{{Cite journal|last=Gionfriddo |first=James P.|author2=Best|date=1 February 1995|title=Grit Use by House Sparrows: Effects of Diet and Grit Size|journal=Condor|volume=97|issue=1|pages=57–67|doi=10.2307/1368983 |jstor=1368983 |url=http://sora.unm.edu/sites/default/files/journals/condor/v097n01/p0057-p0067.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://sora.unm.edu/sites/default/files/journals/condor/v097n01/p0057-p0067.pdf |archive-date=9 October 2022 |url-status=live}}</ref> Some species such as pigeons and some psittacine species do not have a [[gallbladder]].<ref>{{Cite journal |date=2010|title=Complex Evolution of Bile Salts in Birds|journal=The Auk|doi=10.1525/auk.2010.09155 |pmc=2990222|last1=Hagey|first1=Lee R.|last2=Vidal|first2=Nicolas|last3=Hofmann|first3=Alan F. |last4=Krasowski|first4=Matthew D.|volume=127|issue=4 |pages=820–831|pmid=21113274}}</ref> Most birds are highly adapted for rapid digestion to aid with flight.<ref>{{Cite book|last=Attenborough|first=David |title=The Life of Birds|title-link=The Life of Birds |publisher=Princeton University Press|year=1998 |isbn=0-691-01633-X|location=Princeton|author-link=David Attenborough}}</ref> Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration.<ref name="Battley2">{{Cite journal|last1=Battley|first1=Phil F. |last2=Piersma|first2=T|last3=Dietz|first3=MW|last4=Tang|first4=S|last5=Dekinga|first5=A|last6=Hulsman |first6=K|date=January 2000|title=Empirical evidence for differential organ reductions during trans-oceanic bird flight|journal=[[Proceedings of the Royal Society B]]|volume=267|issue=1439|pages=191–195 |doi=10.1098/rspb.2000.0986|pmc=1690512 |pmid=10687826}} (Erratum in ''Proceedings of the Royal Society B'' '''267'''(1461):2567.)</ref>

Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists.<ref name="Gill"/> [[Avian foraging]] strategies can vary widely by species. Many birds [[Gleaning (birds)|glean]] for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek [[Pest (organism)|pest]] [[insect]]s are considered beneficial 'biological control agents' and their presence encouraged in [[biological pest control]] programmes.<ref name="lwa001">{{cite web |url=http://lwa.gov.au/files/products/land-water-and-wool/pf061365/pf061365.pdf |title=Birds on New England wool properties – A woolgrower guide |access-date=17 July 2010 |publisher=Australian Government – Land and Water Australia |work=Land, Water & Wool Northern Tablelands Property Fact Sheet |author=Reid, N. |year=2006 |archive-date=15 March 2011 |archive-url=https://web.archive.org/web/20110315005353/http://lwa.gov.au/files/products/land-water-and-wool/pf061365/pf061365.pdf}}</ref> Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually.<ref>{{cite journal |last1=Nyffeler |first1=M. |last2=Şekercioğlu |first2=Ç. H. |last3=Whelan |first3=C. J. |date=August 2018 |title=Insectivorous birds consume an estimated 400–500 million tons of prey annually |journal=[[The Science of Nature]] |volume=105 |issue=7–8 |page= 47|doi=10.1007/s00114-018-1571-z |pmid=29987431 |pmc=6061143 |bibcode=2018SciNa.105...47N }}</ref>

Nectar feeders such as [[hummingbird]]s, [[sunbird]]s, [[lories and lorikeets|lories, and lorikeets]] amongst others have specially adapted brushy tongues and in many cases bills designed to fit [[Coevolution|co-adapted]] flowers.<ref>{{Cite journal|last1=Paton |first1=D. C. |date=1 April 1989|title=Bills and tongues of nectar-feeding birds: A review of morphology, function, and performance, with intercontinental comparisons |journal=Australian Journal of Ecology |volume=14 |issue=4 |pages=473–506 |doi=10.1111/j.1442-9993.1989.tb01457.x |first2=B.G. |last2=Collins |bibcode=1989AusEc..14..473P }}</ref> [[Kiwi (bird)|Kiwi]]s and [[shorebird]]s with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of [[ecological niche]]s.<ref name="Gill"/><ref>{{Cite journal|last1=Baker |first1=Myron Charles |date=1 April 1973|title=Niche Relationships Among Six Species of Shorebirds on Their Wintering and Breeding Ranges |journal=Ecological Monographs |volume=43 |issue=2 |pages=193–212 |doi=10.2307/1942194 |first2=Ann Eileen Miller |last2=Baker |jstor=1942194|bibcode=1973EcoM...43..193B }}</ref> [[Loon|Diver]]s, [[diving duck]]s, [[penguin]]s and [[auks]] pursue their prey underwater, using their wings or feet for propulsion,<ref name="Burger"/> while aerial predators such as [[sulidae|sulids]], [[kingfisher]]s and [[tern]]s plunge dive after their prey. [[Flamingo]]s, three species of [[prion (bird)|prion]], and some ducks are [[filter feeder]]s.<ref>{{Cite journal|last1=Cherel |first1=Yves |year=2002 |title=Food and feeding ecology of the sympatric thin-billed ''Pachyptila belcheri'' and Antarctic ''P. desolata'' prions at Iles Kerguelen, Southern Indian Ocean |journal=Marine Ecology Progress Series |volume=228 |pages=263–281 |doi=10.3354/meps228263 |last2=Bocher |first2=P |last3=De Broyer |first3=C |last4=Hobson |first4=KA|bibcode=2002MEPS..228..263C |doi-access=free }}</ref><ref>{{Cite journal|last=Jenkin |first=Penelope M. |year=1957 |title=The Filter-Feeding and Food of Flamingoes (Phoenicopteri) |journal=Philosophical Transactions of the Royal Society B |volume=240 |issue=674 |pages=401–493 |doi=10.1098/rstb.1957.0004 |jstor=92549|bibcode=1957RSPTB.240..401J }}</ref> [[Geese]] and [[dabbling duck]]s are primarily grazers.<ref>{{cite book |last1=Hughes |first1=Baz |last2=Green |first2=Andy J. |chapter=Feeding Ecology |editor-last1=Kear |editor-first1= Janet|title=Ducks, Geese and Swans. |publisher=Oxford University Press |year=2005|pages=42–44 |isbn=978-0-19-861008-3 |chapter-url=https://books.google.com/books?id=MfrdBcKd79wC&pg=PA42}}</ref><ref>{{cite journal |title=The Craniolingual Morphology of Waterfowl (Aves, Anseriformes) and Its Relationship with Feeding Mode Revealed Through Contrast-Enhanced X-Ray Computed Tomography and 2D Morphometrics |year=2016 |last1=Li |first1=Zhiheng |last2=Clarke |first2=Julia A. |journal=Evolutionary Biology |volume=43 |issue=1 |pages=12–25 |doi=10.1007/s11692-015-9345-4 |bibcode=2016EvBio..43...12L }}</ref>

Some species, including [[frigatebird]]s, [[gull]]s,<ref>{{cite journal |last1=Takahashi |first1=Akinori |last2=Kuroki |first2=Maki |last3=Niizuma |first3=Yasuaki |last4=Watanuki |first4=Yutaka |title=Parental Food Provisioning Is Unrelated to Manipulated Offspring Food Demand in a Nocturnal Single-Provisioning Alcid, the Rhinoceros Auklet |journal=Journal of Avian Biology |date=December 1999 |volume=30 |issue=4 |pages=486 |doi=10.2307/3677021 |jstor=3677021 }}</ref> and [[skua]]s,<ref>{{Cite journal|last=Bélisle |first=Marc |date=1 August 1995|title=Predation and kleptoparasitism by migrating Parasitic Jaegers |journal=The Condor |volume=97 |issue=3 |pages=771–781 |doi=10.2307/1369185 |url=http://sora.unm.edu/sites/default/files/journals/condor/v097n03/p0771-p0781.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://sora.unm.edu/sites/default/files/journals/condor/v097n03/p0771-p0781.pdf |archive-date=9 October 2022 |url-status=live|author2=Giroux|jstor=1369185 }}</ref> engage in [[kleptoparasitism]], stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of [[great frigatebird]]s stealing from [[masked booby|masked boobies]] estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%.<ref>{{cite journal |last1=Vickery |first1=J. A. |title=The Kleptoparasitic Interactions between Great Frigatebirds and Masked Boobies on Henderson Island, South Pacific |url=https://archive.org/details/sim_condor_1994-05_96_2/page/331 |journal=The Condor |date=May 1994 |volume=96 |issue=2 |pages=331–340 |doi=10.2307/1369318 |jstor=1369318 }}</ref> Other birds are [[scavenger]]s; some of these, like [[vulture]]s, are specialised carrion eaters, while others, like gulls, [[corvid]]s, or other birds of prey, are opportunists.<ref>{{Cite journal|last1=Hiraldo |first1=F. C. |year=1991 |title=Unspecialized exploitation of small carcasses by birds |journal=Bird Studies |volume=38 |issue=3 |pages=200–207 |doi=10.1080/00063659109477089 |last2=Blanco |first2=J. C. |last3=Bustamante |first3=J.|bibcode=1991BirdS..38..200H |hdl=10261/47141 |hdl-access=free }}</ref>