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{{Short description|Domesticated species of bird}}
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{{two other uses|the animal|chicken as human food|Chicken (food)||}}
{{About||the culinary use of chickens|Chicken as food|other uses|Chicken (disambiguation)}}
{{Redirect2|Rooster|Roosters}}
{{Taxobox | name = Chicken | status = {{StatusDomesticated}}
{{Redirect|Cockerel|the Fabergé egg|Cockerel (Fabergé egg)}}
| image = Female pair.jpg
{{Pp-move}}
| image_width = 250px
{{Pp|small=yes}}
| image_caption = A cock (left) and hen (right) roosting together
{{Good article}}
| regnum = [[Animal]]ia
{{Use mdy dates|date=September 2023}}
| phylum = [[Chordate|Chordata]]
{{Speciesbox
| classis = [[Bird|Aves]]
| ordo = [[Galliformes]]
| image = Male and female chicken sitting together.jpg
| image_caption = Male (left) and female (right)
| familia = [[Phasianidae]]
| genus = ''[[Junglefowl|Gallus]]''
| status = DOM
| species = '''''G. gallus domesticus'''''
| genus = Gallus
| species = gallus domesticus
| bionomial authority = [[Carolus Linnaeus|Linnaeus]]
| date = 1758
| synonyms = ''Gallus domesticus'' <small>[[L.]]</small>
| authority = ([[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]])
| range_map = GLW 2 global distributions of c) chickens.tif
| range_map_caption = Chicken distribution
}}
}}
The '''chicken''' ('''''Gallus domesticus''''') is a large and round short-winged [[bird]], [[domestication|domesticated]] from the [[red junglefowl]] of [[Southeast Asia]] around 8,000 years ago. Most chickens are raised for food, providing [[Chicken as food|meat]] and [[egg as food|eggs]]; others are kept as [[pet]]s<ref>{{Cite web |last=Joshua |date=2020-07-27 |title=Chickens and Roosters…As Pets? |url=https://journal.iaabcfoundation.org/roosters-as-pets/ |access-date=2024-12-05 |website=IAABC Foundation Journal}}</ref> or for [[cockfight]]ing.


Chickens are common and widespread domestic animals, with a total population of 26.5 billion {{As of|2023|lc=y}}, and an annual production of more than 50 billion birds. A hen bred for laying can produce over 300 eggs per year. There are numerous [[cultural references to chickens]] in folklore, religion, and literature.
The '''Chicken''' (''Gallus gallus'', sometimes ''G. gallus domesticus'') is a [[Domestication|domesticated]] [[fowl]] likely descended from the wild [[India]]n and [[southeast Asia]]n [[Red Junglefowl]] (''Gallus gallus'') and the related [[Grey Junglefowl]] (''G. sonneratii''). Traditionally it has been widely accepted that the chicken was descended solely from the former, as hybrids of both wild types tended toward sterility; but recent genetic work has revealed that the genotype for yellow skin present in the domestic fowl is not present in what is otherwise its closest kin, the Red Junglefowl. It is deemed most likely, then, that the yellow skin trait in domestic birds originated in the Grey Junglefowl.<ref>Eriksson J, Larson G, Gunnarsson U, Bed'hom B, Tixier-Boichard M, et al. (2008) ''Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken.'' PLoS Genet January 23, 2008 [http://genetics.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pgen.1000010.eor&ct=1].</ref>


== Nomenclature ==
The chicken is one of the most common and widespread [[domestic animals]]. With a population of more than 24 billion in 2003,<ref>according to Firefly Encyclopedia of Birds, Ed. Perrins, Christopher. Buffalo, N.Y.: Firefly Books, Ltd., 2003.</ref> there are more chickens in the world than any other bird. Humans keep chickens primarily as a source of food, with both their [[Chicken (food)|meat]] and their [[egg (food)|eggs]] consumed.


Terms for chickens include:
==Etymology==
In the U.S.A., Canada and Australia, adult male chickens are known as ''[[rooster]]s''; in the UK they are known as ''cocks''.{{Fact|date=April 2008}} Males under a year old are ''cockerels''.<ref>[http://dictionary.reference.com/browse/cockerel cockerel - Definitions from Dictionary.com<!-- Bot generated title -->]</ref> Castrated roosters are called ''[[capon]]s'' (though both surgical and chemical castration are now illegal in some parts of the world). Females over a year old are known as ''hens'', and younger females are ''[[pullet]]s''.<ref>[http://dictionary.reference.com/browse/pullet pullet - Definitions from Dictionary.com<!-- Bot generated title -->]</ref> In Australia and New Zealand (also sometimes in Britain), there is a useful generic term ''chook'' (rhymes with "book") to describe all ages and both genders.<ref>[http://encarta.msn.com/dictionary_/chook.html Definition of "chook" in ''Encarta''. The vernacular use is said to be offensive in this dictionary but it may also be used as a term of jocular familiarity]</ref> Babies are called ''chicks'', and the meat is called ''[[#Chickens as food|chicken]]''.


* ''Biddy'': a chicken, or a newly hatched chicken<ref>{{cite web |url=https://www.dictionary.com/browse/biddy |title=Definition of biddy |publisher=Dictionary.com |access-date=May 7, 2021 |archive-date=May 7, 2021 |archive-url=https://web.archive.org/web/20210507151125/https://www.dictionary.com/browse/biddy |url-status=live}}</ref><ref>{{cite web |url=https://www.collinsdictionary.com/us/dictionary/english/biddy |title=Biddy definition and meaning |publisher=Collins English Dictionary|access-date=May 7, 2021 |archive-date=May 7, 2021 |archive-url=https://web.archive.org/web/20210507010137/https://www.collinsdictionary.com/us/dictionary/english/biddy |url-status=live}}</ref>
"Chicken" was originally the word only for chicks, and the species as a whole was then called ''domestic fowl'', or just ''fowl''. This use of "chicken" survives in the phrase "Hen and Chickens," sometimes used as a [[UK]] [[pub]] or [[theatre]] name, and to name groups of one large and many small rocks or islands in the sea (see for example [[Hen and Chicken Islands]]).
* ''[[Capon]]'': a castrated or [[neutered]] male chicken{{efn|The surgical and chemical castration of chickens is now illegal in some parts of the world.}}
* ''[[Chick (young bird)|Chick]]'': a young chicken<ref>{{cite web |title=Chick |url=https://dictionary.cambridge.org/us/dictionary/english/chick |url-status=live |publisher=Cambridge Dictionary |archive-url=https://web.archive.org/web/20150907132725/http://dictionary.cambridge.org/us/dictionary/english/chick |archive-date=September 7, 2015 }}</ref>
* ''Chook'' {{IPAc-en|tʃ|ʊ|k}}: a chicken (Australia/New Zealand, informal)<ref>{{cite web |title=Chook |url=https://dictionary.cambridge.org/us/dictionary/english/chook |url-status=live |access-date=March 4, 2021 |website=Cambridge Dictionary |archive-url=https://web.archive.org/web/20150907151220/http://dictionary.cambridge.org/us/dictionary/english/chook |archive-date=September 7, 2015 }}</ref>
* ''Cock'': a fertile adult male chicken<ref>{{cite web |title=Cock |url=https://dictionary.cambridge.org/us/dictionary/english/cock |url-status=live |access-date=March 4, 2021 |publisher=Cambridge Dictionary |archive-url=https://web.archive.org/web/20150907102240/http://dictionary.cambridge.org/us/dictionary/english/cock |archive-date=September 7, 2015 }}</ref><ref>{{Cite web |title=Hen |url=https://dictionary.cambridge.org/us/dictionary/english/cock |url-status=live |access-date=March 4, 2021 |publisher=Cambridge Dictionary |archive-url=https://web.archive.org/web/20150907102240/http://dictionary.cambridge.org/us/dictionary/english/cock |archive-date=September 7, 2015 }}</ref>
* ''Cockerel'': a young male chicken<ref>{{cite encyclopedia |url=http://dictionary.reference.com/browse/cockerel |title=Cockerel |publisher=Dictionary Reference |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20160307191527/http://dictionary.reference.com/browse/cockerel |archive-date=March 7, 2016 |url-status=live }}</ref>
* ''Hen'': an adult female chicken<ref>{{cite web |title=Hen noun |url=https://www.merriam-webster.com/dictionary/hen |publisher=[[Merriam-Webster]] |access-date=2 February 2024}}</ref>
* ''Pullet'': a young female chicken less than a year old.<ref>{{cite encyclopedia |url=http://dictionary.reference.com/browse/pullet |title=Pullet |publisher=Dictionary Reference |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20101109014624/http://dictionary.reference.com/browse/pullet |archive-date=November 9, 2010 |url-status=live }}</ref> In the poultry industry, a pullet is a sexually immature chicken less than 22 weeks of age.<ref>{{Cite web |title=Overview of the Poultry Industry |url=https://dese.mo.gov/sites/default/files/aged%20-PoultrySR.pdf |url-status=live |publisher=Missouri Department of Elementary and Secondary Education |page=8 |archive-url=https://web.archive.org/web/20201023230530/https://dese.mo.gov/sites/default/files/aged%20-PoultrySR.pdf |archive-date=October 23, 2020 }}</ref>
* ''Rooster'': a fertile adult male chicken, especially in North America. Originated in the 18th century, possibly as a euphemism to avoid the sexual connotation of the word ''cock''.<ref>{{Cite web |title=Definition of Rooster |url=https://www.merriam-webster.com/dictionary/rooster |publisher=Merriam-Webster |access-date=March 6, 2021 |archive-date=April 22, 2021 |archive-url=https://web.archive.org/web/20210422030634/https://www.merriam-webster.com/dictionary/rooster |url-status=live}}</ref><ref name="Rawson">[http://www.americanheritage.com/content/why-do-we-say-17 Hugh Rawson] {{Webarchive |url=https://web.archive.org/web/20170701144833/http://www.americanheritage.com/content/why-do-we-say-17 |date=July 1, 2017 }} "Why Do We Say...? Rooster", ''American Heritage'', August–September 2006.</ref><ref name="Online Etymology Dictionary">[https://www.etymonline.com/search?q=rooster Online Etymology Dictionary] {{Webarchive |url=https://web.archive.org/web/20201111222713/https://www.etymonline.com/search?q=rooster |date=November 11, 2020 }} Entry for ''rooster (n.)'', May 2019</ref>
* ''Yardbird'': a chicken (southern United States, dialectal)<ref name="berhardt">{{cite book |last=Berhardt |first=Clyde E. B. |title=I Remember: Eighty Years of Black Entertainment, Big Bands |year=1986 |publisher=[[University of Pennsylvania Press]] |isbn=978-0-8122-8018-0 |oclc=12805260 |page=153}}</ref>


''Chicken'' can mean a ''chick'', as in [[William Shakespeare]]'s play ''[[Macbeth]]'', where [[Macduff (Macbeth)|Macduff]] laments the death of "all my pretty chickens and their dam".<ref>[[William Shakespeare|Shakespeare, William]], ''[[Macbeth]]'', Act 4 Scene 3, lines 217–229.</ref> The usage is preserved in placenames such as the [[Hen and Chicken Islands]].<ref>{{Cite web |title=Chicken |url=https://www.merriam-webster.com/dictionary/chicken |url-status=live |access-date=March 4, 2021 |website=Merriam Webster Dictionary |archive-url=https://web.archive.org/web/20080821163810/http://www.merriam-webster.com/dictionary/chicken |archive-date=August 21, 2008 }}</ref> In older sources, and still often in trade and scientific contexts, chickens as a species are described as ''common fowl'' or ''domestic fowl''.<ref>{{cite book |last=Stevens |first=Lewis |title=Genetics and evolution of the domestic fowl |pages=11 and throughout |year=1991 |publisher=[[Cambridge University Press]] |isbn=978-0-521-40317-7 |url=https://books.google.com/books?id=S-DXqQ9UOmAC&dq=%22domestic+fowl%22&pg=PA11}}</ref>
==General biology and habitat==
[[Image:Day old chick black background.jpg|thumb|200px||left|A day-old chick]]
Chickens in nature may live for five to eleven years depending on the breed.<ref>[http://www.ruleworks.co.uk/cgi-bin/TUfaq.exe?Guide=Poultry&Category=Poultry%20-%20General#q9 The Poultry Guide - A to Z and FAQs<!-- Bot generated title -->]</ref> In commercial intensive farming, a meat Chicken generally lives only six weeks before slaughter.<ref>[http://www.animalsaustralia.org/factsheets/broiler_chickens.php Broiler Chickens Fact Sheet // Animals Australia<!-- Bot generated title -->]</ref> A [[free range]] or [[Organic (food)|organic]] meat Chicken will usually be slaughtered at about 14 weeks. Hens of special laying [[Breed (animal)|breeds]] may produce as many as 300 eggs a year. After 12 months, the hen's egg-laying ability starts to decline, and commercial laying hens are then slaughtered and used in baby foods, pet foods, pies and other processed foods.<ref>[http://observer.guardian.co.uk/foodmonthly/story/0,,662799,00.html Ten weeks to live | Food and drink | Life and Health<!-- Bot generated title -->]</ref> The world's oldest Chicken, according to the [[Guinness Book of World Records]], died of heart failure when she was 16.<ref>Smith, Jamon. [http://www.tuscaloosanews.com/apps/pbcs.dll/article?AID=/20060806/NEWS/608060400/1007/NEWS02 Tuscaloosanews.com "World’s oldest chicken starred in magic shows, was on 'Tonight Show’"], ''[[Tuscaloosa News]]'' (Alabama, USA). [[6 August 2006]]. Retrieved on [[26 Feb 2008]].</ref>


== Description ==
Roosters can usually be differentiated from hens by their striking plumage, marked by long flowing tails and shiny, pointed feathers on their necks and backs (the ''hackles'' and ''saddle'')—these are often colored differently from the hackles and saddles of females.


{{multiple image
However, in some breeds, such as the [[Sebright (chicken)|Sebright]], the cock has only slightly pointed neck feathers, the same colour as the hen's. The identification must be made by looking at the comb, or eventually from the development of [[Spur (disambiguation)|spur]]s on the male's legs (in a few breeds and in certain hybrids the male and female chicks may be differentiated by colour). Adult Chickens have a fleshy crest on their heads called a ''[[cockscomb|comb or cockscomb]]'', and hanging flaps of skin either side under their beaks called ''[[wattle (anatomy)|wattles]]''. These organs help to cool the [[bird]] by redirecting blood flow to the skin.{{Fact|date=October 2007}} <!-- Why don't all birds have them then? More likely a social signal. --> Both the adult male and female have wattles and combs, but in most breeds these are more prominent in males.
| width1 = 150
| image1 = Rooster portrait2.jpg
| caption1 = [[Comb (anatomy)|Comb]] of male
| width2 = 200
| image2 = Hen Comb (cropped).jpg
| caption2 = Comb of female, generally smaller
}}


Chickens are relatively large [[bird]]s, [[Diurnality|active by day]]. The body is round, the legs are unfeathered in most breeds, and the wings are short.<ref name="Smithsonian"/> Wild [[junglefowl]] can [[bird flight|fly]]; chickens and their [[flight muscle]]s are too heavy to allow them to fly more than a short distance.<ref>{{cite web |last1=Geggel |first1=Laura |title=Forget About the Road. Why Are Chickens So Bad at Flying? |url=https://www.livescience.com/57139-why-chickens-cannot-fly.html |website=Live Science |access-date=3 February 2024 |date=8 December 2016 |archive-date=April 4, 2024 |archive-url=https://web.archive.org/web/20240404115622/https://www.livescience.com/57139-why-chickens-cannot-fly.html |url-status=live }}</ref> Size and coloration vary widely between breeds.<ref name="Smithsonian">{{cite web |title=Chicken |url=https://nationalzoo.si.edu/animals/domestic-chicken |publisher=Smithsonian's National Zoo & Conservation Biology Institute |access-date=2 February 2024 |archive-date=February 2, 2024 |archive-url=https://web.archive.org/web/20240202165324/https://nationalzoo.si.edu/animals/domestic-chicken |url-status=live }}</ref> Newly-hatched chicks of both modern and heritage varieties weigh the same, about {{cvt|37|g|oz}}. Modern varieties however grow much faster; by day 35 a Ross 708 [[broiler]] may weigh {{cvt|1.8|kg|lb}} as against the {{cvt|1.05|kg|lb}} of a heritage chicken of the same age.<ref name="Schmidt Persia 2009">{{cite journal |last=Schmidt |first=C.J. |last2=Persia |first2=M.E. |last3=Feierstein |first3=E. |last4=Kingham |first4=B. |last5=Saylor |first5=W.W. |title=Comparison of a modern broiler line and a heritage line unselected since the 1950s |journal=Poultry Science |volume=88 |issue=12 |date=2009 |doi=10.3382/ps.2009-00055 |doi-access=free |pages=2610–2619}}</ref>
In the wild, chickens often scratch at the soil to search for seeds, insects and even larger animals such as [[lizard]]s or young [[mice]].{{Fact|date=January 2008}}


Adult chickens of both sexes have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin on either side under their beaks called [[Wattle (anatomy)|wattles]]; combs and wattles are [[Sexual dimorphism|more prominent in males]]. Some breeds have a [[mutation]] that causes extra feathering under the face, giving the appearance of a beard.<ref name=plosg>{{cite journal |last1=Guo |first1=Ying |last2=Gu |first2=Xiaorong |last3=Sheng |first3=Zheya |last4=Wang |first4=Yanqiang |last5=Luo |first5=Chenglong |last6=Liu |first6=Ranran |last7=Qu |first7=Hao |last8=Shu |first8=Dingming |last9=Wen |first9=Jie |last10=Crooijmans |first10=Richard P. M. A. |last11=Carlborg |first11=Örjan |last12=Zhao |first12=Yiqiang |last13=Hu |first13=Xiaoxiang |last14=Li |first14=Ning |display-authors=5 |title=A Complex Structural Variation on Chromosome 27 Leads to the Ectopic Expression of HOXB8 and the Muffs and Beard Phenotype in Chickens |journal=PLOS Genetics |volume=12 |issue=6 |date=2 June 2016 |pmid=27253709 |pmc=4890787 |doi=10.1371/journal.pgen.1006071 |doi-access=free |page=e1006071}}</ref>
Domestic chickens are not capable of long distance flight, although lighter birds are generally capable of flying for short distances, such as over fences or into trees (where they would naturally roost). Chickens will sometimes fly to explore their surroundings, but usually do so only to flee perceived danger. Because of the risk of escape, chickens raised in open-air pens often have one of their wings clipped by the breeder—the tips of the longest feathers on one of the wings are cut, resulting in unbalanced flight which the bird cannot sustain for more than a few meters, and it is thus discouraged from flying at all. {{Fact|date=December 2007}}


Chickens are [[omnivore]]s.<ref>{{cite web |url=http://www.ideas-4-pets.co.uk/info.-on-chicken-care |title=Info on Chicken Care |access-date=August 13, 2008 |website=Ideas-4-pets.co.uk |year=2003 |archive-url=https://web.archive.org/web/20150625195044/http://www.ideas-4-pets.co.uk/info.-on-chicken-care |archive-date=June 25, 2015 |url-status=dead }}</ref> In the wild, they scratch at the soil to search for seeds, insects, and animals as large as [[lizard]]s, small snakes,<ref>{{cite web |url=https://www.youtube.com/watch?v=45i1hZfUQhk |archive-url=https://ghostarchive.org/varchive/youtube/20211211/45i1hZfUQhk| archive-date=December 11, 2021 |url-status=live|title=Chicken Kills Rattlesnake |last=D Lines |date=July 27, 2013 |access-date=March 13, 2019 |publisher=[[YouTube]]}}{{cbignore}}</ref> and young [[mouse|mice]].<ref>{{cite web |url=https://gworrell.freeyellow.com/chickenfaq.html |title=Frequently asked questions about chickens & eggs |access-date=August 13, 2008 |website=Gworrell.freeyellow.com |author=Gerard P.Worrell AKA "Farmer Jerry" |archive-url=https://web.archive.org/web/20080916202420/http://gworrell.freeyellow.com/chickenfaq.html |archive-date=September 16, 2008 |url-status=live }}</ref> A chicken may live for 5–10 years, depending on the [[breed]].<ref>{{cite web |url=http://www.ruleworks.co.uk/cgi-bin/TUfaq.exe?Guide=Poultry&Category=Poultry%20-%20General#q9 |title=The Poultry Guide – A to Z and FAQs |website=Ruleworks.co.uk |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20101128085141/http://ruleworks.co.uk/cgi-bin/TUfaq.exe?Guide=Poultry&Category=Poultry%20-%20General#q9 |archive-date=November 28, 2010 |url-status=dead }}</ref> The world's oldest known chicken lived for 16 years.<ref>{{cite web|last1=Smith |first1=Jamon |url=https://www.tuscaloosanews.com/article/DA/20060806/News/606120381/TL |title=World's oldest chicken starred in magic shows, was on 'Tonight Show' |archive-url=https://web.archive.org/web/20190220002804/https://www.tuscaloosanews.com/apps/pbcs.dll/article?AID=%2F20060806%2FNEWS%2F608060400%2F1007%2FNEWS02 |archive-date=February 20, 2019 |website=[[Tuscaloosa News]] |location=Alabama, USA |date=August 6, 2006 |access-date=May 18, 2020 |url-status=live}}</ref>
Chickens are gregarious birds and live together as a [[herd|flock]]. They have a communal approach to the [[avian incubation|incubation]] of eggs and raising of young. Individual chickens in a flock will dominate others, establishing a "[[pecking order]]," with dominant individuals having priority for access to food and nesting locations. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Adding hens—especially younger birds—to an existing flock, can lead to violence and injury.<ref>[http://stonehead.wordpress.com/2006/06/28/introducing-new-hens-to-a-flock/ Introducing new hens to a flock « Musings from a Stonehead<!-- Bot generated title -->]</ref>


Chickens are [[gregarious]], living in [[herd|flocks]], and [[Egg incubation|incubate eggs]] and raise young communally. Individual chickens dominate others, establishing a [[Dominance hierarchy|pecking order]]; dominant individuals take priority for access to food and nest sites. The concept of dominance, involving pecking, was described in female chickens by [[Thorleif Schjelderup-Ebbe]] in 1921 as the "pecking order".<ref>{{cite journal |last=Perrin |first=P. G. |year=1955 |title='Pecking order' 1927–54 |journal=American Speech |volume=30 |issue=4 |pages=265–268|doi=10.2307/453561 |jstor=453561 | issn = 0003-1283}}</ref><ref>{{cite book |last=Schjelderup-Ebbe |first=T. |year=1975 |chapter=Contributions to the social psychology of the domestic chicken [Schleidt M., Schleidt, W. M., translators] |editor-last=Schein |editor-first=M. W. |title=Social Hierarchy and Dominance. Benchmark Papers in Animal Behavior |volume=3 |location=Stroudsburg, Pennsylvania |publisher=Dowden, Hutchinson and Ross |pages=35–49}} (Reprinted from ''Zeitschrift für Psychologie'', 1922, 88:225–252.)</ref> Male chickens tend to leap and use their claws in conflicts.<ref>{{cite journal |last=Rajecki |first=D. W. |year=1988 |title=Formation of leap orders in pairs of male domestic chickens |journal=Aggressive Behavior |volume=14 |issue=6 |pages=425–436|doi=10.1002/1098-2337(1988)14:6<425::AID-AB2480140604>3.0.CO;2-#|s2cid=141664966 }}</ref> Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox.<ref>{{cite web |last=AFP |date=March 12, 2019 |title=Chickens 'teamed up to kill fox' at Brittany farming school |url=https://www.theguardian.com/world/2019/mar/12/chickens-teamed-up-to-kill-fox-at-brittany-farming-school |url-status=live |archive-url=https://web.archive.org/web/20190313002528/https://www.theguardian.com/world/2019/mar/12/chickens-teamed-up-to-kill-fox-at-brittany-farming-school |archive-date=March 13, 2019 |access-date=March 13, 2019 |website=Theguardian.com}}</ref>
Hens will try to lay in nests that already contain eggs, and have been known to move eggs from neighbouring nests into their own. Some farmers use fake eggs made from plastic or stone (or golf balls) to encourage hens to lay in a particular location. The result of this behavior is that a flock will use only a few preferred locations, rather than having a different nest for every bird.


[[File:Rooster_crowing_small.ogv|thumb|Crowing (with audio)]]
Hens can also be extremely stubborn about always laying in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other.
[[Image:Rooster crowing.jpg|thumb|Rooster crowing during daylight hours]]
Contrary to popular belief, roosters do not crow only at dawn, but may crow at any time of the day or night. Their crowing—a loud and sometimes shrill call—is a territorial signal to other roosters. However, crowing may also result from sudden disturbances within their surroundings. Hens cluck loudly after laying an egg, and also to call their chicks.


A male's crowing is a loud and sometimes shrill call, serving as a territorial signal to other males,<ref>{{Cite news |url=https://phys.org/news/2015-07-cock-roosters-crow.html |title=Top cock: Roosters crow in pecking order |website=Phys.org |access-date=January 14, 2018 |archive-url=https://web.archive.org/web/20180115124738/https://phys.org/news/2015-07-cock-roosters-crow.html |archive-date=January 15, 2018 |url-status=live }}</ref> and in response to sudden disturbances within their surroundings. Hens cluck loudly after laying an [[egg]] and to call their chicks. Chickens give different [[warning call]]s to indicate that a [[Predation|predator]] is approaching from the air or on the ground.<ref>{{cite journal |last1=Evans |first1=Christopher S. |last2=Evans |first2=Linda |last3=Marler |first3=Peter |title=On the meaning of alarm calls: functional reference in an avian vocal system |journal=Animal Behaviour |date=July 1993 |volume=46 |issue=1 |pages=23–38 |doi=10.1006/anbe.1993.1158 |s2cid=53165305 |s2cid-access=free }}</ref>
In 2006, scientists researching the ancestry of birds "turned on" a chicken [[recessive gene]], ''talpid2'', and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. John Fallon, the overseer of the project, stated that chickens have "...retained the ability to make teeth, under certain conditions..."<ref>[http://abcnews.go.com/Technology/story?id=1666805 Scientists Find Chickens Retain Ancient Ability to Grow Teeth] Ammu Kannampilly, ABC News, [[2006-02-27]]. Retrieved [[2007-10-01]].</ref>


== Reproduction and life-cycle ==
== Courting ==
When a rooster finds food he may call the other chickens to eat it first. He does this by clucking in a high pitch as well as picking up and dropping the food. This behavior can also be observed in mother hens, calling their chicks. In some cases the rooster will drag the wing opposite the hen on the ground, while circling her. This is part of chicken courting ritual. When a hen is used to coming to his "call" the rooster may mount the hen and proceed with the fertilization.


To initiate courting, some roosters may dance in a circle around or near a hen (a circle dance), often lowering the wing which is closest to the hen.<ref name="grandin69">{{cite book |title=Animals in Translation |last1=Grandin |first1=Temple |author-link1=Temple Grandin |last2=Johnson |first2=Catherine |year=2005 |publisher=[[Scribner's]] |location=New York City |isbn=978-0-7432-4769-6 |pages=[https://archive.org/details/animalsintransla00gran/page/69 69–71] |url-access=registration |url=https://archive.org/details/animalsintransla00gran/page/69 }}</ref> The dance triggers a response in the hen<ref name="grandin69" /> and when she responds to his call, the rooster may mount the hen and proceed with the mating. Mating typically involves a sequence in which the male approaches the female and performs a waltzing display. If the female is unreceptive, she runs off; otherwise, she crouches, and the male mounts, treading with both feet on her back. After copulation the male does a tail-bending display.<ref>{{cite journal |last1=Cheng |first1=Kimberly M. |last2=Burns |first2=Jeffrey T. |title=Dominance Relationship and Mating Behavior of Domestic Cocks: A Model to Study Mate-Guarding and Sperm Competition in Birds |journal=[[Ornithological Applications|The Condor]] |date=August 1988 |volume=90 |issue=3 |pages=697–704 |doi=10.2307/1368360 |jstor=1368360 }}</ref>
==Going broody==


Sperm transfer occurs by [[cloaca]]l contact between the male and female, in an action called the 'cloacal kiss'.<ref name="Briskie1997">{{cite journal |last=Briskie |first=J. V. |author2=R. Montgomerie |year=1997 |title=Sexual Selection and the Intromittent Organ of Birds |journal=Journal of Avian Biology |volume=28 |issue=1 |pages=73–86 |doi=10.2307/3677097 |jstor=3677097}}</ref> As with all birds, [[reproduction]] is controlled by a [[neuroendocrine cell|neuroendocrine]] system,<ref>{{Cite journal |last1=Dufour |first1=Sylvie |last2=Quérat |first2=Bruno |last3=Tostivint |first3=Hervé |last4=Pasqualini |first4=Catherine |last5=Vaudry |first5=Hubert |last6=Rousseau |first6=Karine |date=April 2020 |title=Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications |url=https://journals.physiology.org/doi/full/10.1152/physrev.00009.2019 |journal=Physiological Reviews |volume=100 |issue=2 |pages=869–943 |doi=10.1152/physrev.00009.2019 |pmid=31625459 |issn=0031-9333}}</ref> the [[Gonadotropin-Releasing Hormone-I neuron]]s in the [[hypothalamus]]. Reproductive hormones including [[estrogen]], [[progesterone]], and [[gonadotropin]]s ([[luteinizing hormone]] and [[follicle-stimulating hormone]]) initiate and maintain sexual maturation changes. Reproduction declines with age, thought to be due to a decline in GnRH-I-N.<ref name="Bain-et-al-2016">{{cite journal |last1=Bain |first1=M. M. |last2=Nys |first2=Y. |last3=Dunn |first3=I.C. |title=Increasing persistency in lay and stabilising egg quality in longer laying cycles. What are the challenges? |journal=[[British Poultry Science]] |publisher=[[Taylor & Francis]] |volume=57 |issue=3 |date=May 3, 2016 |doi=10.1080/00071668.2016.1161727 |pages=330–338 |pmid=26982003 |pmc=4940894 |s2cid=17842329 |doi-access=free }}</ref>
{{Citations missing|date=December 2007}}
[[Image:Chicken eggs.jpg|thumb|left|Chicken eggs vary in color depending on the hen, typically ranging from bright white to shades of brown and even blue, green, and recently reported purple (found in South Asia) (Araucana varieties).]]
Under natural conditions most birds lay only until a clutch is complete, and they will then incubate all the eggs. Many domestic hens will also do this &ndash; and are then said to ''go broody''. The broody hen will stop laying and instead will focus on the incubation of the eggs (a full clutch is usually about 12 eggs). She will ''sit'' or ''set'' fast on the nest, protesting or pecking in defense if disturbed or removed, and she will rarely leave the nest to eat, drink, or dust-bathe. While brooding, the hen maintains the nest at a constant temperature and humidity, as well as turning the eggs regularly during the first part of the incubation. To stimulate broodiness, an owner may place many artificial eggs in the nest, or to stop it they may place the hen in an elevated cage with an open wire floor.
At the end of the incubation period (about 21 days), the eggs, if fertile, will hatch. Development of the egg starts only when incubation begins, so they all hatch within a day or two of each other, despite perhaps being laid over a period of two weeks or so. Before hatching the hen can hear the chicks peeping inside the eggs, and will gently cluck to stimulate them to break out of their shells. The chick begins by ''pipping'' &ndash; pecking a breathing hole with its [[egg tooth]] towards the blunt end of the egg, usually on the upper side. It will then rest for some hours, absorbing the remaining egg-yolk and withdrawing the blood supply from the membrane beneath the shell (used earlier for breathing through the shell). It then enlarges the hole, gradually turning round as it goes, and eventually severing the blunt end of the shell completely to make a lid. It crawls out of the remaining shell and its wet down dries out in the warmth of the nest.


[[File:Newly-hatched chickens.jpg|thumb|Newly hatched chicks]]
The hen will usually stay on the nest for about two days after the first egg hatches, and during this time the newly-hatched chicks live off the egg yolk they absorb just before hatching. Any eggs not fertilized by a rooster will not hatch, and the hen eventually loses interest in these and leaves the nest. After hatching the hen fiercely guards the chicks, and will ''brood'' them when necessary to keep them warm, at first often returning to the nest at night. She leads them to food and water &ndash; she will call them to edible items, but rarely feeds them directly. She continues to care for them until they are several weeks old, when she will gradually lose interest and eventually start to lay again.
Modern egg-laying breeds rarely go broody, and those that do often stop part-way through the incubation. However, some "utility" (general purpose) breeds, such as the [[Cochin (chicken)|Cochin]], [[Cornish (chicken)|Cornish]] and [[Silkie (chicken)|Silkie]], do regularly go broody, and they make excellent mothers, not only for chicken eggs but also for those of other species -- even those with much smaller or larger eggs and different incubation periods, such as [[quail]], [[pheasant]]s, [[turkey (bird)|turkey]]s or [[Goose|geese]]. Chicken eggs can also be hatched under a broody duck, with varied success.


Hens often try to lay in nests that already contain eggs and sometimes move eggs from neighbouring nests into their own. A flock thus uses only a few preferred locations, rather than having a different nest for every bird.<ref>{{cite journal |last1=Sherwin |first1=C.M. |last2=Nicol |first2=C.J. |year=1993 |title=Factors influencing floor-laying by hens in modified cages |journal=[[Applied Animal Behaviour Science]] |volume=36 |issue=2–3 |pages=211–222 |doi=10.1016/0168-1591(93)90011-d}}</ref> Under natural conditions, most birds lay only until a [[Clutch (eggs)|clutch]] is complete; they then incubate all the eggs. This is called "going [[Broodiness|broody]]". The hen sits on the nest, fluffing up or pecking defensively if disturbed. She rarely leaves the nest until the eggs have hatched.<ref name="Puff-up-Feathers">{{cite web |title=Why Do Chickens Puff up Their Feathers? I 4 Reasons Explained|date= August 8, 2020|url= https://chickenandchicksinfo.com/why-do-chickens-puff-up-their-feathers/ |access-date=June 16, 2021 |archive-date=June 18, 2021 |archive-url=https://web.archive.org/web/20210618091939/https://chickenandchicksinfo.com/why-do-chickens-puff-up-their-feathers/ |url-status=live}}</ref>
==Artificial incubation==
Chicken egg incubation can successfully occur artificially as well. Nearly all fertilized Chicken eggs will hatch after 21 days of good conditions - 99.5 °[[Fahrenheit|F]] (37.5 °[[Celsius|C]]) and around 55% [[relative humidity]] (increase to 70% in the last three days of incubation to help soften egg shell). Eggs must be turned regularly (usually three to eight times each week) during the first part of the incubation. If the eggs aren't turned, the [[embryo]] inside will stick to the shell and may hatch with physical defects. Some incubators turn the eggs automatically. This turning mimics the natural process &ndash; an incubating hen will stand up several times a day and shift the eggs around with her [[beak]]. However, if the egg is turned during the last week of incubation the chick may have difficulty settling in the correct hatching position.


Eggs of chickens from the high-altitude region of [[Tibet]] have special physiological adaptations that result in a higher hatching rate in low oxygen environments. When eggs are placed in a hypoxic environment, chicken embryos from these populations express much more [[hemoglobin]] than embryos from other chicken populations. This hemoglobin has a greater affinity for oxygen, binding oxygen more readily.<ref>{{Cite journal |last1=Zhang |first1=H. |last2=Wang |first2=X.T. |last3=Chamba |first3=Y. |last4=Ling |first4=Y.|last5=Wu|first5=C.X. |date=October 2008|title=Influences of Hypoxia on Hatching Performance in Chickens with Different Genetic Adaptation to High Altitude |journal=Poultry Science |volume=87 |issue=10 |pages=2112–2116 |doi=10.3382/ps.2008-00122 |pmid=18809874 |doi-access=free}}</ref>
Many commercial incubators are industrial-sized with shelves holding tens of thousands of eggs at a time, with rotation of the eggs a fully automated process. Home incubators are boxes holding from half a dozen to 75 eggs; they are usually electrically powered, but in the past some were heated with an oil or paraffin lamp.
[[Image:Eggess.JPG|thumb|200px|A free range egg (left) next to a battery egg (right).]]


Fertile chicken eggs hatch at the end of the incubation period, about 21 days; the chick uses its [[egg tooth]] to break out of the shell.<ref name="grandin69"/> Hens remain on the nest for about two days after the first chick hatches; during this time the newly hatched chicks feed by absorbing the internal [[yolk sac]].<ref>{{cite journal |last1=Ali |first1=A. |last2=Cheng |first2=K.M. |year=1985 |title=Early egg production in genetically blind (rc/rc) chickens in comparison with sighted (Rc+/rc) controls |journal=Poultry Science |volume=64 |issue=5 |pages=789–794 |doi=10.3382/ps.0640789 |pmid=4001066 |doi-access=free }}</ref> The hen guards her chicks and broods them to keep them warm. She leads them to food and water and calls them towards food. The chicks [[Imprinting (psychology)|imprint]] on the hen and subsequently follow her continually. She continues to care for them until they are several weeks old.<ref name="Edgar Held Jones Troisi 2016 p. 2">{{cite journal |last1=Edgar |first1=Joanne |last2=Held |first2=Suzanne |last3=Jones |first3=Charlotte |last4=Troisi |first4=Camille |title=Influences of Maternal Care on Chicken Welfare |journal=Animals |volume=6 |issue=1 |date=2016-01-05 |pmid=26742081 |pmc=4730119 |doi=10.3390/ani6010002 |doi-access=free |page=2}}</ref>
==Chickens as food==
{{main|Chicken (food)}}


Inbreeding of White Leghorn chickens tends to cause [[inbreeding depression]] expressed as reduced egg number and delayed sexual maturity.<ref>{{cite journal |last1=Sewalem |first1=A. |last2=Johansson |first2=K. |last3=Wilhelmson |first3=M. |last4=Lillpers |first4=K. |title=Inbreeding and inbreeding depression on reproduction and production traits of White Leghorn lines selected for egg production traits |journal=British Poultry Science |volume=40 |issue=2 |date=1999 |doi=10.1080/00071669987601 |pages=203–208|pmid=10465386 }}</ref> Strongly inbred Langshan chickens display obvious inbreeding depression in reproduction, particularly for traits such as age when the first egg is laid and egg number.<ref>{{cite journal |last1=Xue |first1=Qian |last2=Li |first2=Guohui |last3=Cao |first3=Yuxia |last4=Yin |first4=Jianmei |last5=Zhu |first5=Yunfen |last6=Zhang |first6=Huiyong |last7=Zhou |first7=Chenghao |last8=Shen |first8=Haiyu |last9=Dou |first9=Xinhong |last10=Su |first10=Yijun |last11=Wang |first11=Kehua |last12=Zou |first12=Jianmin |last13=Han |first13=Wei |title=Identification of genes involved in inbreeding depression of reproduction in Langshan chickens |journal=Animal Bioscience |volume=34 |issue=6 |date=1 June 2021 |issn=2765-0189 |pmid=33152217 |pmc=8100482 |doi=10.5713/ajas.20.0248 |pages=975–984}}</ref>
The [[meat]] of the Chicken, also called "chicken," is a type of poultry meat. Because of its relatively low cost, chicken is one of the most used meats in the world. Nearly all parts of the bird can be used for food, and the meat is cooked in many different ways around the world. Popular chicken dishes include [[fried chicken]], [[chicken soup]], [[Buffalo wings]], [[tandoori chicken]], [[butter chicken]], and [[Hainanese chicken rice|chicken rice]]. Chicken is also a staple of [[fast food]] restaurants such as [[KFC]], [[McDonald's]], and [[Burger King]]. Commercially produced chicken usually has a fairly neutral flavor and texture,{{Fact|date=October 2007}} and is used as a reference point for describing other foods; many are said to "[[Tastes like chicken|taste like chicken]]" if they are indistinctive.[[Image:Dominique Hen.JPG|thumb|200px|A Dominique Hen sitting.]]


==Chickens as pets==
== Origin ==
<!--PLEASE stop squashing everything up, spaces and blank lines are intentional, THANK YOU-->
Chickens can make good [[companion animal]]s and can be tamed by hand feeding, but — roosters, particularly — can sometimes become aggressive. Some have advised against keeping them around very young children.


=== Phylogeny ===
While some cities in the [[United States]] allow chickens as pets, the practice is not approved in all localities. Some communities ban only roosters, allowing the quieter hens. The so called "urban hen movement" harks back to the days when Chicken keeping was much more common, and involves the keeping of small groups of hens in areas where they may not be expected, such as closely populated cities and suburban areas. City ordinances, zoning regulations or health boards may determine whether chickens may be kept.[http://www.mypetchicken.com/chickenFAQ.aspx#InViolation] A general requirement is that the birds be confined to the owner's property, not allowed to roam freely. There may be strictures on how far from human dwellings a coop may be located, etc.<ref> My Pet Chicken: Links [http://www.mypetchicken.com/Links.aspx gives links to regulations of some major U.S. cities that allow chickens.]</ref>


[[File:Red Junglefowl.jpg|thumb|[[Red junglefowl]], the wild ancestor of the chicken ]]
Chickens are generally low-maintenance. The major challenge is protecting the birds from predators such as [[dog]]s, [[raccoon]]s and [[fox]]es. A bird left out at night is likely to be killed by a predator. Chickens are usually kept in a [[roost]] at night and a pen in the day (unless they are [[free-range]]). The floor is covered with bedding such as straw or wood shavings, which, with the high-nitrogen droppings, can go into a compost pile.


Water or ground-dwelling fowl similar to modern [[partridge]]s, in the [[Galliformes]], the [[order (biology)|order]] of bird that chickens belong to, survived the [[Cretaceous–Paleogene extinction event]] that killed all tree-dwelling birds and their [[dinosaur]] relatives.<ref>{{cite journal |last=Pennisi |first=Elizabeth |author-link=Elizabeth Pennisi |title=Quaillike creatures were the only birds to survive the dinosaur-killing asteroid impact |journal=Science |date=May 24, 2018 |doi=10.1126/science.aau2802}}</ref> Chickens are descended primarily from the [[red junglefowl]] (''Gallus gallus'') and are scientifically classified as the same species.<ref name=nature>{{cite journal |title=A genetic variation map for chicken with 2.8 million single nucleotide polymorphisms |journal=Nature |date=December 9, 2004 |volume=432 |issue=7018 |pages=717–722 |doi=10.1038/nature03156 |pmid=15592405 |pmc=2263125 |bibcode=2004Natur.432..717B |last1=Wong |first1=G. K. |last2=Liu |first2=B. |last3=Wang |first3=J. |last4=Zhang |first4=Y. |last5=Yang |first5=X. |last6=Zhang |first6=Z. |last7=Meng |first7=Q. |last8=Zhou |first8=J. |last9=Li |first9=D. |last10=Zhang |first10=J. |last11=Ni |first11=P. |last12=Li |first12=S. |display-authors=6}}</ref> Domesticated chickens freely interbreed with populations of red junglefowl.<ref name=nature /> The domestic chicken has subsequently hybridised with [[grey junglefowl]], [[Sri Lankan junglefowl]] and [[green junglefowl]];<ref name="Lawal">{{cite journal |last1=Lawal |first1=Raman Akinyanju |last2=Martin |first2=Simon H. |last3=Vanmechelen |first3=Koen |last4=Vereijken |first4=Addie |last5=Silva |first5=Pradeepa |last6=Al-Atiyat |first6=Raed Mahmoud |last7=Aljumaah |first7=Riyadh Salah |last8=Mwacharo |first8=Joram M. |last9=Wu |first9=Dong-Dong |last10=Zhang |first10=Ya-Ping |last11=Hocking |first11=Paul M. |last12=Smith |first12=Jacqueline |last13=Wragg |first13=David |last14=Hanotte |first14=Olivier |display-authors=6 |title=The wild species genome ancestry of domestic chickens |journal=BMC Biology |date=December 2020 |volume=18 |issue=1 |pages=13 |doi=10.1186/s12915-020-0738-1 |pmid=32050971 |pmc=7014787 |doi-access=free}}</ref> a gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl (''G. sonneratii'').<ref>{{cite journal |last1=Eriksson |first1=Jonas |last2=Larson |first2=Greger |last3=Gunnarsson |first3=Ulrika |last4=Bed'hom |first4=Bertrand |last5=Tixier-Boichard |first5=Michele |last6=Strömstedt |first6=Lina |last7=Wright |first7=Dominic |last8=Jungerius |first8=Annemieke |last9=Vereijken |first9=Addie |last10=Randi |first10=Ettore |last11=Jensen |first11=Per |last12=Andersson |first12=Leif |display-authors=6 |title=Identification of the Yellow Skin Gene Reveals a Hybrid Origin of the Domestic Chicken |journal=PLOS Genetics |date=February 29, 2008 |volume=4 |issue=2 |pages=e1000010 |doi=10.1371/journal.pgen.1000010 |pmid=18454198 |pmc=2265484 |doi-access=free }}</ref> It is estimated that chickens share between 71 and 79% of their genome with red junglefowl.<ref name="Lawal"/>
It can be satisfying to gather from one's own mini-flock of hens eggs one knows are fresh and wholesome. Roosters are not required, as hens lay eggs whether or not they are fertilized (see [[Egg (food)]]). Fresh egg [[yolk]]s are "perky" and float above the white. Yolk color varies. According to Gail Damerow's handbook, "Egg yolks get their color from ''xanthophyll'', a natural yellow-orange pigment in green plants and yellow corn, and the same pigment that colors the skin and shanks of yellow-skinned hens. The exact color of a yolk depends on the source of the xanthophyll." A subsequent table ascribes raw yolks colored "orange to dark yellow" to "green feed, yellow corn."<ref>Storey's Guide to Raising Chickens: Care, Feeding, Facilities by Gail Damerow, Pownal VT: Storey Books, (c) 1995. p. 141. [http://www.storey.com/authors/authors.php/author/022 for publisher's author entry]</ref>


=== Domestication ===
If your hens are allowed to forage or are fed additional greens, their eggs may be additionally healthy. Barb Gorski, a Pennsylvania farmer of pastured poultry, had some of her meat chickens and eggs analyzed under the USDA-supported Sustainable Agriculture Research and Education (SARE) program. According to the laboratory results, "Eggs of the pastured chickens contained 34% less cholesterol, 10% less fat, 40% more vitamin A, twice as much omega-6 fatty acid, and four times as much omega-3 fatty acid as the USDA standard."<ref>Pastured Poultry Products: Summary, SARE 1999 [http://www.sare.org/reporting/report_viewer.asp?pn=FNE99-248&ry=1999&rf=0]</ref>


{{further|Domestication}}
While the bulk of your pet chickens' diet should be a balanced commercial mix, for household chickens "green feed" can be as simple as poison-free, short grass clippings from lawn mowing. And if you have chickweed in your lawn every spring, your flock will be happy to consume it — directly, if you have an adequate pen that can be moved about the lawn or adequate yard fencing; chickens will happily forage for other plants, seeds, and insects for an hour or so a day. (Be sure not to leave them out in hot sun, and certainly not without water for any length of time.)


[[File:Chicken domestication and dispersal.svg|thumb|upright=2|Chicken domestication and dispersal;<ref name="Lawal"/> possibility of early arrival in Americas<ref name="Borrell 2007"/><ref name="Storey 2007"/>]]
Additionally, chickens can take care of a good amount of otherwise wasted food, such as meal leavings, pulverized eggshells and old (but not rotted) produce. Damerow recommends leftover baked goods, fruit, or vegetable peelings, excess milk in modest amounts; advises against making such scraps the sole diet, or including raw potato peels "which chickens can't easily digest,...anything spoiled or rotten,...strong-tasting foods like onions, garlic, or fish."<ref>Storey's Guide to Raising Chickens: Care, Feeding, Facilities by Gail Damerow, Pownal VT: Storey Books, (c) 1995. p. 51. [http://www.storey.com/authors/authors.php/author/022 for publisher's author entry]</ref>


According to one early study, a single domestication event of the [[red junglefowl]] in present-day [[Thailand]] gave rise to the modern chicken with minor transitions separating the modern breeds.<ref name="oneMatriarch">{{citation |title=One subspecies of the red junglefowl (Gallus gallus gallus) suffices as the matriarchic ancestor of all domestic breeds |first1=A. |last1=Fumihito |first2=T. |last2=Miyake |first3=S. |last3=Sumi |first4=M. |last4=Takada |first5=S. |last5=Ohno |first6=N. |last6=Kondo |journal=PNAS |date=December 20, 1994 |volume=91 |number=26 |pages=12505–12509 |doi=10.1073/pnas.91.26.12505 |pmid=7809067 |bibcode=1994PNAS...9112505F |pmc=45467 |doi-access=free }}</ref> The red junglefowl is well adapted to take advantage of the vast quantities of seed produced during the end of the [[Bamboo#Mass flowering|multi-decade bamboo seeding cycle]], to boost its own reproduction.<ref>{{citation |first=Rick |last=King |title=Rat Attack |date=February 24, 2009 |journal=Nova and National Geographic Television |url=https://www.pbs.org/wgbh/nova/nature/rat-attack.html |access-date=August 25, 2017 |archive-url=https://web.archive.org/web/20170823151419/http://www.pbs.org/wgbh/nova/nature/rat-attack.html |archive-date=August 23, 2017 |url-status=live }}</ref> In domesticating the chicken, humans took advantage of the red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply.<ref>{{citation |first=Rick |last=King |title=Plant vs. Predator |date=February 1, 2009 |journal=NOVA |url=https://www.pbs.org/wgbh/nova/nature/plant-vs-predator.html |access-date=August 25, 2017 |archive-url=https://web.archive.org/web/20170821123509/http://www.pbs.org/wgbh/nova/nature/plant-vs-predator.html |archive-date=August 21, 2017 |url-status=live }}</ref>
In addition to the bonuses of food and fertilizer from chickens as pets, their behaviour can be entertaining. It can also be very educational to become acquainted on a small scale with livestock husbandry and food production.


Exactly when and where the chicken was domesticated remains controversial. Genomic studies estimate that the chicken was domesticated 8,000 years ago<ref name="Lawal"/> in Southeast Asia and spread to China and India 2,000 to 3,000 years later. Archaeological evidence supports domestic chickens in Southeast Asia well before 6000&nbsp;BC, China by 6000&nbsp;BC and India by 2000&nbsp;BC.<ref name=Lawal/><ref name="West Zhou 1988">{{cite journal |last1=West |first1=B. |last2=Zhou |first2=B.X. |year=1988 |title=Did chickens go north? New evidence for domestication |journal=J. Archaeol. Sci. |volume=14 |issue= 5 |pages=515–533 |doi=10.1016/0305-4403(88)90080-5 |bibcode=1988JArSc..15..515W }}</ref><ref>{{cite journal |last1=Al-Nasser |first1=A. |last2=Al-Khalaifa |first2=H. |last3=Al-Saffar |first3=A. |last4=Khalil |first4=F. |last5=Albahouh |first5=M. |last6=Ragheb |first6=G. |last7=Al-Haddad |first7=A. |last8=Mashaly |first8=M. |title=Overview of chicken taxonomy and domestication |journal=World's Poultry Science Journal |date=June 1, 2007 |volume=63 |issue=2 |pages=285–300 |doi=10.1017/S004393390700147X |s2cid=86734013 }}</ref> A landmark 2020 Nature study that fully sequenced 863 chickens across the world suggests that all domestic chickens originate from a single domestication event of red junglefowl whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar. These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups. Analysis of the most popular commercial breed shows that the White Leghorn breed possesses a mosaic of divergent ancestries inherited from subspecies of red junglefowl.<ref>{{cite journal |title=863 genomes reveal the origin and domestication of chicken |year=2020 |doi=10.1038/s41422-020-0349-y |s2cid=220050312 |last1=Wang |first1=Ming-Shan |last2=Thakur|first2=Mukesh |last3=Peng |first3=Min-Sheng |last4=Jiang |first4=Yu |last5=Frantz |first5=Laurent Alain François |last6=Li|first6=Ming |last7=Zhang|first7=Jin-Jin |last8=Wang |first8=Sheng |last9=Peters |first9=Joris |last10=Otecko |first10=Newton Otieno |last11=Suwannapoom |first11=Chatmongkon |last12=Guo |first12=Xing |journal=Cell Research |volume=30 |issue=8 |pages=693–701 |pmid=32581344 |pmc=7395088 |display-authors=6}}</ref><ref>{{cite journal |last1=Liu |first1=Yi-Ping |last2=Wu |first2=Gui-Sheng |last3=Yao |first3=Yong-Gang |last4=Miao |first4=Yong-Wang |last5=Luikart |first5=Gordon |last6=Baig |first6=Mumtaz |last7=Beja-Pereira |first7=Albano |last8=Ding |first8=Zhao-Li |last9=Palanichamy |first9=Malliya Gounder |last10=Zhang |first10=Ya-Ping |display-authors=6 |title=Multiple maternal origins of chickens: Out of the Asian jungles |journal=Molecular Phylogenetics and Evolution |date=January 2006 |volume=38 |issue=1 |pages=12–19 |doi=10.1016/j.ympev.2005.09.014 |pmid=16275023 |bibcode=2006MolPE..38...12L }}</ref><ref>{{cite journal |last1=Zeder |first1=Melinda A. |last2=Emshwiller |first2=Eve |last3=Smith |first3=Bruce D. |last4=Bradley |first4=Daniel G. |title=Documenting domestication: the intersection of genetics and archaeology |journal=Trends in Genetics |date=March 2006 |volume=22 |issue=3 |pages=139–155 |doi=10.1016/j.tig.2006.01.007 |pmid=16458995 }}</ref>
In [[Asia]], chickens with striking plumage have long been kept for ornamental purposes, including feather-footed varieties such as the [[Cochin (chicken)|Cochin]] from [[Vietnam]], the [[Silkie]] from [[China]], and the extremely long-tailed [[Phoenix chicken|Phoenix]] from [[Japan]]. Asian ornamental varieties were imported into the [[United States]] and [[Great Britain]] in the late 1800s. Distinctive American varieties of chickens have been developed from these Asian breeds. Poultry fanciers began keeping these ornamental birds for exhibition, a practice that continues today. Individuals in rural communities commonly keep chickens for both ornamental and practical value. [[Zoo]]s sometimes use chickens instead of [[insecticide]]s to control [[insect]] populations.


== Dispersal ==
==Chickens in agriculture==
[[Image:Chickens drinking.jpg|left|250px|thumb|[[Free range]] chickens]]
{{globalize/USA}} In the [[United States]], chickens were raised primarily on family [[farm]]s until roughly 1960. Originally, the primary value in poultry keeping was eggs, and meat was considered a byproduct of egg production.<ref>U.S. Department of Agriculture - National Agricultural Statistics Service: Trends in U.S. Agriculture - [http://www.usda.gov/nass/pubs/trends/broiler.htm Broiler Industry]</ref> Its supply was less than the demand, and poultry was expensive. Except in hot weather, eggs can be shipped and stored without refrigeration for some time before going bad; this was important in the days before widespread refrigeration.


=== Austronesia ===
Farm flocks tended to be small because the hens largely fed themselves through foraging, with some supplementation of grain, scraps, and waste products from other farm ventures. Such feedstuffs were in limited supply, especially in the winter, and this tended to regulate the size of the farm flocks. Soon after poultry keeping gained the attention of agricultural researchers (around 1896), improvements in nutrition and management made poultry keeping more profitable and businesslike.


[[File:Map showing prehistoric diffusion of domestic chickens (Gallus gallus) into the Pacific via the Austronesian migrations (Thomson, Lebrasseur, & Austin, 2014).png|thumb|upright=2|Prehistoric introduction of domesticated chickens into [[Oceania]] from the [[Philippines]] via [[Neolithic]] [[Austronesian expansion]] (starting at c. 4000 [[Before present|BP]]), inferred from genetic markers on ancient and modern chicken DNA (Thomson ''et al.'', 2014)<ref name="Thomson"/>]]
Prior to about 1910, chicken was served primarily on special occasions or Sunday dinner. Poultry was shipped live or killed, plucked, and packed on ice (but not [[Disembowelment|eviscerated]]). The "whole, ready-to-cook broiler" wasn't popular until the [[Fifties]], when end-to-end refrigeration and sanitary practices gave consumers more confidence. Before this, poultry were often cleaned by the neighborhood [[butcher]], though cleaning poultry at home was a commonplace kitchen skill.


A word for the domestic chicken (''*manuk'') is part of the reconstructed [[Proto-Austronesian language]], indicating they were [[Domesticated plants and animals of Austronesia|domesticated]] by the [[Austronesian peoples]] since ancient times. Chickens, together with dogs and pigs, were carried throughout the entire range of the prehistoric Austronesian maritime migrations to [[Island Southeast Asia]], [[Micronesia]], [[Island Melanesia]], [[Polynesia]], and [[Madagascar]], starting from at least 3000&nbsp;BC from [[Indigenous Taiwanese|Taiwan]].<ref name= Thomson>{{cite journal |last=Thomson |first=Vicki A. |others= et al. |title=Using ancient DNA to study the origins and dispersal of ancestral Polynesian chickens across the Pacific |journal=Proceedings of the National Academy of Sciences |date=April 2014 |volume=111 |issue=13 |pages=4826–4831 |doi=10.1073/pnas.1320412111 |pmid=24639505 |pmc=3977275 |bibcode=2014PNAS..111.4826T |doi-access=free }}</ref><ref name= Piper>{{cite book |first1=Philip J. |last1=Piper |editor1-first=Philip J. |editor1-last=Piper |editor2-first=Hirofumi |editor2-last=Matsumura |editor3-first=David |editor3-last=Bulbeck |title=New Perspectives in Southeast Asian and Pacific Prehistory |chapter=The Origins and Arrival of the Earliest Domestic Animals in Mainland and Island Southeast Asia: A Developing Story of Complexity |publisher=[[ANU Press]] |volume=45 |series=terra australis |year=2017 |isbn=9781760460945 |chapter-url =http://press-files.anu.edu.au/downloads/press/n2320/html/ch15.xhtml |access-date =May 5, 2023 |archive-date =November 28, 2022 |archive-url =https://web.archive.org/web/20221128075413/https://press-files.anu.edu.au/downloads/press/n2320/html/ch15.xhtml |url-status =live}}</ref><ref>{{cite book |url=https://books.google.com/books?id=FJ9ULYwX3zgC&pg=PA56 |title=The Cambridge History of the Pacific Islanders |first=Malama |last=Meleisea |date=March 25, 2004 |publisher=[[Cambridge University Press]] |page=56 |access-date=March 13, 2019 |archive-url=https://web.archive.org/web/20160913140948/https://books.google.com/books?id=FJ9ULYwX3zgC&pg=PA56 |archive-date=September 13, 2016 |url-status=live |isbn=9780521003544}}</ref><ref>{{cite book |url=https://books.google.com/books?id=tlSspaBLkhoC&pg=PA411 |title=Anthropological Genetics: Theory, Methods and Applications |first=Michael H. |last=Crawford |date=March 13, 2019 |publisher=[[Cambridge University Press]] |page=411 |access-date=March 13, 2019 |via=Google Books |archive-url=https://web.archive.org/web/20160913143140/https://books.google.com/books?id=tlSspaBLkhoC&pg=PA411 |archive-date=September 13, 2016 |url-status=live |isbn=9780521546973}}</ref> These chickens might have been introduced during [[pre-Columbian]] times to [[South America]] via [[Polynesians|Polynesian]] seafarers, but evidence for this is still putative.<ref name= Neumann>{{cite news |last=Neumann |first=Scott |title=Study: The Chicken Didn't Cross The Pacific To South America |url=https://www.npr.org/sections/thetwo-way/2014/03/18/291182073/study-the-chicken-didnt-cross-the-pacific-to-south-america |access-date=May 5, 2023 |work=The Two Way |agency=NPR |date=March 18, 2014 |archive-date=May 5, 2023 |archive-url=https://web.archive.org/web/20230505060006/https://www.npr.org/sections/thetwo-way/2014/03/18/291182073/study-the-chicken-didnt-cross-the-pacific-to-south-america |url-status=live }}</ref>
Two kinds of [[poultry]] were generally offered: broilers or "spring chickens," young male chickens, a byproduct of the egg industry, which were sold when still young and tender (generally under 3 pounds live weight); and "fowls" or "stewing hens," also a byproduct of the egg industry, which were old hens past their prime for laying.<ref>"The Dollar Hen", [[Milo Hastings]], Arcadia Press, 1909; reprint Norton Creek Press, 2003, Robert Plamondon, Ed., pp. 145-150.</ref> This is no longer practiced; modern meat chickens are a different breed. Egg-type chicken carcasses no longer appear in stores.


=== Americas ===
The major milestone in 20th century poultry production was the discovery of Vitamin-D (named in 1922),<ref >"Poultry Nutrition", Ray Ewing, Ray Ewing Press, Third Edition, 1947, page 754.</ref> which made it possible to keep chickens in confinement year-round. Before this, chickens did not thrive during the winter (due to lack of sunlight), and egg production, incubation, and meat production in the off-season were all very difficult, making poultry a seasonal and expensive proposition. Year-round production lowered costs, especially for broilers.


The possibility that domestic chickens were in the Americas before Western contact is debated by researchers, but blue-egged chickens, found only in the Americas and Asia, suggest an Asian origin for early American chickens. A lack of data from Thailand, Russia, the Indian subcontinent, Southeast Asia and Sub-Saharan Africa makes it difficult to lay out a clear map of the spread of chickens in these areas; better description and genetic analysis of local breeds threatened by [[extinction]] may also help with research into this area.<ref name= CHOF/> Chicken bones from the [[Arauco Peninsula]] in [[Zona Sur|south-central Chile]] were radiocarbon dated as pre-Columbian, and DNA analysis suggested they were related to prehistoric populations in Polynesia.<ref name="Borrell 2007">{{cite journal |last1=Borrell |first1=Brendan |title=DNA reveals how the chicken crossed the sea |journal=Nature |date=June 1, 2007 |volume=447 |issue=7145 |pages=620–621 |doi=10.1038/447620b |pmid=17554271 |bibcode=2007Natur.447R.620B |s2cid=4418786 |doi-access=free }}</ref><ref name="Storey 2007">{{cite journal |last=Storey |first=A. A. |others= et al. |title=Radiocarbon and DNA evidence for a pre-Columbian introduction of Polynesian chickens to Chile |journal=Proceedings of the National Academy of Sciences |date=June 19, 2007 |volume=104 |issue=25 |pages=10335–10339 |doi=10.1073/pnas.0703993104 |pmid=17556540 |pmc=1965514 |bibcode=2007PNAS..10410335S |doi-access=free }}</ref> However, further study of the same bones cast doubt on the findings.<ref>{{cite journal |last=Gongora |first=Jaime |others= et al. |year=2008 |title=Indo-European and Asian origins for Chilean and Pacific chickens revealed by mtDNA |journal=PNAS |volume=105 |issue=30 |pages=10308–10313 |doi=10.1073/pnas.0801991105 |pmid=18663216 |pmc=2492461 |bibcode=2008PNAS..10510308G |doi-access=free }}</ref><ref name= Thomson14>{{cite journal |last=Thomson |first=Vicki A.
At the same time, egg production was increased by scientific breeding. After a few false starts, such as the Maine Experiment Station's failure at improving egg production,<ref>"The Dollar Hen", [[Milo Hastings]], Arcadia Press, 1909; reprint Norton Creek Press, 2003, Robert Plamondon, Ed., pp. 225-229.</ref> success was shown by Professor Dryden at the Oregon Experiment Station.<ref>Dryden, James. Poultry Breeding and Management. Orange Judd Press, 1916.</ref>
|others= et al. |title=Using ancient DNA to study the origins and dispersal of ancestral Polynesian chickens across the Pacific |journal=Proceedings of the National Academy of Sciences |date=April 1, 2014 |volume=111 |issue=13 |pages=4826–4831 |doi=10.1073/pnas.1320412111 |pmid=24639505 |pmc=3977275 |bibcode=2014PNAS..111.4826T |doi-access=free }}</ref>


=== Eurasia ===
Improvements in production and quality were accompanied by lower labor requirements. In the [[Thirties]] through the early Fifties, 1,500 hens was considered to be a full-time job for a farm family. In the late Fifties, egg prices had fallen so dramatically that farmers typically tripled the number of hens they kept, putting three hens into what had been a single-bird cage or converting their floor-confinement houses from a single deck of roosts to triple-decker roosts. Not long after this, prices fell still further and large numbers of egg farmers left the business. This marked the beginning of the transition from family farms to larger, vertically integrated operations.


Chicken remains have been difficult to date, given the small and fragile bird bones; this may account for discrepancies in dates given by different sources. Archaeological evidence is supplemented by mentions in historical texts from the last few centuries BC, and by depictions in prehistoric artworks, such as across Central Asia.<ref name= Peters24>{{cite journal |last=Peters |first=Carli |others= et al. |title= Archaeological and molecular evidence for ancient chickens in Central Asia |journal= Nature Communications |volume=15 |issue=1 |date=2024-04-02 |page=2697 |issn=2041-1723 |pmid=38565545 |pmc=10987595 |doi=10.1038/s41467-024-46093-2|bibcode=2024NatCo..15.2697P }}</ref> Chickens were widespread throughout southern Central Asia by the 4th century BC.<ref name= Peters24/>
Robert Plamondon<ref>[http://www.plamondon.com Plamondon.com: the home of Robert Plamondon and all his works!<!-- Bot generated title -->]</ref> reports that the last family chicken farm in his part of Oregon, Rex Farms, had 30,000 layers and survived into the [[Nineties]]. But the standard laying house of the surviving operations is around 125,000 hens.


Middle Eastern chicken remains go back to a little earlier than 2000&nbsp;BC in [[Syria]].<ref name="CHOF">The Cambridge History of Food, 2000, [[Cambridge University Press]], Vol. 1, pp. 496-499</ref> Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. During the [[Hellenistic period]] (4th–2nd centuries BC), in the southern [[Levant]], chickens began to be widely domesticated for food.<ref name= pmid26195775>{{cite journal |last1=Perry-Gal |first1=Lee |last2=Erlich |first2=Adi |last3=Gilboa |first3=Ayelet |last4=Bar-Oz |first4=Guy |date=August 11, 2015 |title=Earliest economic exploitation of chicken outside East Asia: Evidence from the Hellenistic Southern Levant |journal=Proceedings of the National Academy of Sciences |volume=112 |issue=32 |pages=9849–9854 |bibcode=2015PNAS..112.9849P |doi=10.1073/pnas.1504236112 |pmc=4538678 |pmid=26195775 |doi-access=free}}</ref> The first pictures of chickens in Europe are found on [[Corinth, Greece|Corinthian]] [[pottery]] of the 7th century BC.<ref>{{cite book |url=https://books.google.com/books?id=NrIapgM4LwQC&pg=PA176 |title=Regional Greek Cooking |first1=Dean |last1=Karayanis |first2=Catherine |last2=Karayanis |date=March 13, 2019 |publisher=[[Hippocrene Books]] |page=176 |access-date=March 13, 2019 |via=Google Books |archive-url=https://web.archive.org/web/20160913141141/https://books.google.com/books?id=NrIapgM4LwQC&pg=PA176 |archive-date=September 13, 2016 |url-status=live |isbn=9780781811460}}</ref><ref>{{cite book |url=https://books.google.com/books?id=Xwq1lunLkuoC&pg=PA207 |title=Cooking with the Bible: Biblical Food, Feasts, and Lore |first1=Anthony F. |last1=Chiffolo |first2=Rayner W. |last2=Hesse |date=March 13, 2019 |publisher=[[Greenwood Publishing Group]] |page=207 |access-date=March 13, 2019 |via=Google Books |archive-url=https://web.archive.org/web/20160913080305/https://books.google.com/books?id=Xwq1lunLkuoC&pg=PA207 |archive-date=September 13, 2016 |url-status=live |isbn=9780313334108}}</ref>
This fall in profitability was accompanied by a general fall in prices to the consumer, allowing poultry and eggs to lose their status as luxury foods.


Breeding increased under the [[Roman Empire]] and reduced in the [[Middle Ages]].<ref name= CHOF/> [[DNA sequencing|Genetic sequencing]] of chicken bones from archaeological sites in Europe revealed that in the [[High Middle Ages]] chickens became less aggressive and began to lay eggs earlier in the breeding season.<ref name= brown>{{cite journal |last1=Brown |first1=Marley |title=Fast Food |journal=Archaeology |date=Sep–Oct 2017 |volume=70 |issue=5 |page=18 |url=https://www.archaeology.org/issues/269-1709/from-the-trenches/5820-trenches-europe-chicken-domestication |access-date=July 25, 2019 |issn=0003-8113 |archive-date=July 25, 2019 |archive-url=https://web.archive.org/web/20190725160925/https://www.archaeology.org/issues/269-1709/from-the-trenches/5820-trenches-europe-chicken-domestication |url-status=live }}</ref>
The [[vertical integration]] of the egg and poultry industries was a late development, occurring after all the major technological changes had been in place for years (including the development of modern broiler rearing techniques, the adoption of the Cornish Cross broiler, the use of laying cages, etc.).


=== Africa ===
By the late Fifties, poultry production had changed dramatically. Large farms and packing plants could grow birds by the tens of thousands. Chickens could be sent to [[slaughterhouse]]s for [[butcher]]ing and processing into prepackaged commercial products to be frozen or shipped fresh to markets or wholesalers. Meat-type chickens currently grow to market weight in six to seven weeks whereas only fifty years ago it took three times as long.<ref>Havenstein, G.B., P.R. Ferket, and M.A. Qureshi, 2003a. Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci. 82:1500-1508</ref> This is due to genetic selection and nutritional modifications (and not the use of growth hormones, which are illegal for use in poultry in the US and many other countries). Once a meat consumed only occasionally, the common availability and lower cost has made chicken a common meat product within developed nations. Growing concerns over the [[cholesterol]] content of [[red meat]] in the 1980s and 1990s further resulted in increased consumption of chicken.


Chickens reached Egypt via the Middle East for purposes of [[cockfighting]] about 1400&nbsp;BC and became widely bred in Egypt around 300&nbsp;BC.<ref name="CHOF"/> Three possible routes of introduction into Africa around the early first millennium AD could have been through the Egyptian [[Nile River|Nile]] Valley, the East Africa Roman-Greek or Indian trade, or from Carthage and the Berbers, across the [[Sahara Desert|Sahara]]. The earliest known remains are from [[Mali]], [[Nubia]], East Coast, and [[South Africa]] and date back to the middle of the first millennium AD.<ref name= CHOF/>
Today, eggs are produced on large egg ranches on which environmental parameters are controlled. Chickens are exposed to artificial light cycles to stimulate egg production year-round. In addition, it is a common practice to induce [[molt]]ing through manipulation of light and the amount of food they receive in order to further increase egg size and production.


== Diseases ==
On average, a chicken lays one egg a day for a number of days (a "clutch"), then does not lay for one or more days, then lays another clutch. Originally, the hen presumably laid one clutch, became broody, and incubated the eggs. Selective breeding over the centuries has produced hens that lay more eggs than they can hatch. Some of this progress was ancient, but most occurred after 1900. In 1900, average egg production was 83 eggs per hen per year. In 2000, it was well over 300.


{{main |Poultry disease}}
In the United States, laying hens are butchered after their second egg laying season. In Europe, they are generally butchered after a single season. The laying period begins when the hen is about 18-20 weeks old (depending on breed and season). Males of the egg-type breeds have little commercial value at any age, and all those not used for breeding (roughly fifty percent of all egg-type chickens) are killed soon after hatching. The old hens also have little commercial value. Thus, the main sources of poultry meat 100 years ago (spring chickens and stewing hens) have both been entirely supplanted by meat-type broiler chickens.


[[File:Pesse oujheas H9N2 tanfla.JPG|thumb|8 day old chick with [[avian influenza]] ]]
Traditionally, chicken production was distributed across the entire agricultural sector. In the Twentieth Century, it gradually moved closer to major cities to take advantage of lower shipping costs. This had the undesirable side effect of turning the chicken manure from a valuable fertilizer that could be used profitably on local farms to an unwanted byproduct. This trend may be reversing itself due to higher disposal costs on the one hand and higher fertilizer prices on the other, making farm regions attractive once more.


Chickens are susceptible both to [[Parasitism|parasite]]s such as [[mite]]s, and to [[Poultry disease|diseases]] caused by [[pathogen]]s such as [[bacteria]] and [[virus]]es. The parasite ''[[Dermanyssus gallinae]]'' feeds on blood, causing irritation and reducing egg production, and acts as a vector for bacterial diseases such as [[salmonellosis]] and [[Borrelia anserina|spirochaetosis]].<ref name="Schiavone Pugliese 2022">{{Cite journal |last1=Schiavone |first1=Antonella |last2=Pugliese |first2=Nicola |last3=Otranto |first3=Domenico |last4=Samarelli |first4=Rossella |last5=Circella |first5=Elena |last6=De Virgilio |first6=Caterina |last7=Camarda |first7=Antonio |date=2022-01-20 |title=''Dermanyssus gallinae'': the long journey of the poultry red mite to become a vector |journal=Parasites & Vectors |volume=15 |issue=1 |pages=29 |doi=10.1186/s13071-021-05142-1 |pmid=35057849 |issn=1756-3305 |pmc=8772161 |doi-access=free }}</ref>
[[Image:2004chicken.PNG|thumb|right|250px|Chicken headcount in 2004]]
Viral diseases include [[avian influenza]].<ref>{{cite journal |last1=Barjesteh |first1=Neda |last2=O'Dowd |first2=Kelsey |last3=Vahedi |first3=Seyed Milad |title=Antiviral responses against chicken respiratory infections: Focus on avian influenza virus and infectious bronchitis virus |journal=Cytokine |date=March 2020 |volume=127 |pages=154961 |doi=10.1016/j.cyto.2019.154961 |pmid=31901597|pmc=7129915 }}</ref>


== Use by humans ==
From the farmer's point of view, eggs used to be practically the same as currency, with general stores buying eggs for a stated price per dozen. Egg production peaks in the early spring, when farm expenses are high and income is low. On many farms, the flock was the most important source of income, though this was often not appreciated by the farmers, since the money arrived in many small payments. Eggs were a farm operation where even small children could make a valuable contribution.


===Distribution===
=== Farming ===
[[FAO]] reports that China was the top chicken market in 2004 followed by the USA.


{{Main|Poultry farming}}
==Issues with mass production==
===Humane treatment===
[[Image:Industrial-Chicken-Coop.JPG|thumb|350px|[[Industrial agriculture|Battery]] chickens]]


Chickens are common and widespread domestic animals, with a total population of 23.7 billion {{As of|2018|lc=y}}.<ref>{{cite web|title=Number of chickens worldwide from 1990 to 2018.|url=https://www.statista.com/statistics/263962/number-of-chickens-worldwide-since-1990/|access-date=February 23, 2020|website=Statista|archive-date=November 27, 2020|archive-url=https://web.archive.org/web/20201127124744/https://www.statista.com/statistics/263962/number-of-chickens-worldwide-since-1990/|url-status=live}}</ref> More than 50 billion chickens are reared annually as a source of meat and eggs.<ref>{{Cite web |url=https://www.ciwf.org.uk/farm-animals/chickens/ |title=About chickens |publisher=[[Compassion in World Farming]] |access-date=April 25, 2017 |archive-url=https://web.archive.org/web/20170426063521/https://www.ciwf.org.uk/farm-animals/chickens/ |archive-date=April 26, 2017 |url-status=live }}</ref> In the United States alone, more than 8 billion chickens are slaughtered each year for meat,<ref>{{Cite web |url=https://usda.library.cornell.edu/concern/publications/pg15bd88s |title=Poultry Slaughter Annual Summary |last=Fereira |first=John |website=usda.mannlib.cornell.edu |access-date=April 25, 2017 |archive-url=https://web.archive.org/web/20170426063701/http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1497 |archive-date=April 26, 2017 |url-status=live }}</ref> and more than 300 million chickens are reared for egg production.<ref>{{Cite web |url=https://usda.library.cornell.edu/concern/publications/1v53jw96n |title=Chickens and Eggs Annual Summary |last=Fereira |first=John |website=usda.mannlib.cornell.edu |access-date=April 25, 2017 |archive-url=https://web.archive.org/web/20170426061324/http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1509 |archive-date=April 26, 2017 |url-status=live }}</ref> The vast majority of poultry is raised in [[Intensive animal farming|factory farms]]. According to the [[Worldwatch Institute]], 74% of the world's poultry meat and 68% of eggs are produced this way.<ref>{{cite web |title=Towards Happier Meals In A Globalized World |url=http://www.worldwatch.org/towards-happier-meals-globalized-world |publisher=[[Worldwatch Institute]] |access-date=May 29, 2014 |archive-url=https://web.archive.org/web/20140529153518/http://www.worldwatch.org/towards-happier-meals-globalized-world |archive-date=May 29, 2014 |url-status=dead }}</ref> An alternative to intensive poultry farming is [[free-range]] farming. Friction between these two main methods has led to long-term issues of [[ethical consumerism]]. Opponents of [[intensive farming]] argue that it harms the environment, creates human health risks and is inhumane towards [[Sentience in animals|sentient animals]].<ref>{{cite journal |last1=Ilea |first1=Ramona Cristina |title=Intensive Livestock Farming: Global Trends, Increased Environmental Concerns, and Ethical Solutions |journal=Journal of Agricultural and Environmental Ethics |date=April 2009 |volume=22 |issue=2 |pages=153–167 |doi=10.1007/s10806-008-9136-3 |bibcode=2009JAEE...22..153I |s2cid=154306257 }}</ref> Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment.<ref>{{cite journal |last1=Tilman |first1=David |last2=Cassman |first2=Kenneth G. |last3=Matson |first3=Pamela A. |last4=Naylor |first4=Rosamond |last5=Polasky |first5=Stephen |title=Agricultural sustainability and intensive production practices |journal=Nature |date=August 2002 |volume=418 |issue=6898 |pages=671–677 |doi=10.1038/nature01014 |pmid=12167873 |bibcode=2002Natur.418..671T |s2cid=3016610 }}</ref> Chickens farmed for meat are called [[broiler]]s. Broiler breeds typically take less than six weeks to reach slaughter size,<ref>{{cite web |url=https://www.animalsaustralia.org/factsheets/broiler_chickens.php |title=Broiler Chickens Fact Sheet |website=Animals Australia |access-date=August 29, 2010 |archive-url=https://web.archive.org/web/20100712123234/http://www.animalsaustralia.org/factsheets/broiler_chickens.php |archive-date=July 12, 2010 |url-status=live }}</ref> some weeks longer for [[free range]] and [[Organic (food)|organic]] broilers.<ref>{{cite web |title=Chickens Farmed for Meat |url=https://www.ciwf.org.uk/farm-animals/chickens/meat-chickens/ |publisher=[[Compassion in World Farming]] |access-date=2 February 2024 |archive-date=September 21, 2024 |archive-url=https://web.archive.org/web/20240921105646/https://www.ciwf.org.uk/farm-animals/chickens/meat-chickens/ |url-status=live }}</ref>
[[Animal welfare]] groups have frequently targeted the poultry industry for engaging in practices which they believe to be inhumane. Many animal welfare advocates object to killing chickens for food, the "[[factory farming|factory farm conditions]]" under which they are raised, methods of transport, and slaughter. [[PETA]] and other groups have repeatedly conducted undercover investigations at chicken farms and slaughterhouses which they allege confirm their claims of cruelty.<ref>[http://www.kentuckyfriedcruelty.com/u-cok.asp Kentucky Fried Cruelty :: Undercover Investigations :: Compassion Over Killing Investigation<!-- Bot generated title -->]</ref>


[[File:Florida chicken house.jpg|thumb|A commercial chicken house with open sides raising broiler pullets for meat]]
Laying hens are routinely [[debeaking|debeaked]] to prevent fighting. Because beaks are sensitive, trimming them without anaesthesia is considered inhumane by some. It is also argued that the procedure causes life-long discomfort. Conditions in intensive chicken farms may be unsanitary, allowing the proliferation of diseases such as [[salmonella]] and [[E coli]]. Chickens may be raised in total darkness.
Rough handling and crowded transport during various weather conditions and the failure of existing stunning systems to render the birds unconscious before slaughter have also been cited as welfare concerns.


Chickens farmed primarily for eggs are called layer hens. The UK alone consumes more than 34 million eggs per day.<ref>{{Cite web |url=https://www.egginfo.co.uk/egg-facts-and-figures/industry-information/data |title=UK Egg Industry Data |website=Official Egg Info |access-date=April 25, 2017 |archive-url=https://web.archive.org/web/20161230000509/https://www.egginfo.co.uk/egg-facts-and-figures/industry-information/data |archive-date=December 30, 2016 |url-status=live }}</ref> Hens of some breeds can produce over 300 eggs per year; the highest authenticated rate of egg laying is 371 eggs in 364 days.<ref>{{cite book |last1=Glenday |first1=Craig |title=Guinness World Records 2011 |date=April 26, 2011 |publisher=[[Jim Pattison Group]] |isbn=978-0440423102 |page=286}}</ref> After 12 months of laying, the commercial hen's egg-laying ability declines to the point where the flock is commercially unviable. Hens, particularly from [[battery cage]] systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from around seven years to less than two years.<ref name="Browne">{{cite news |url=https://www.theguardian.com/lifeandstyle/2002/mar/10/foodanddrink.features1 |work=The Guardian |location=London |title=Ten weeks to live |first=Anthony |last=Browne |date=March 10, 2002 |access-date=April 28, 2010 |archive-url=https://web.archive.org/web/20080516080228/http://observer.guardian.co.uk/foodmonthly/story/0,,662799,00.html |archive-date=May 16, 2008 |url-status=live }}</ref> In the UK and Europe, laying hens are then slaughtered and used in processed foods, or sold as 'soup hens'.<ref name="Browne" /> In some other countries, flocks are sometimes [[Forced molting|force moulted]] rather than being slaughtered to re-invigorate egg-laying. This involves complete withdrawal of food (and sometimes water) for 7–14 days<ref name="Patwardhan and King, (2011)">{{cite journal |last1=Patwardhan |first1=D. |last2=King |first2=A. |year=2011 |title=Review: feed withdrawal and non feed withdrawal moult |journal=World's Poultry Science Journal |volume=67 |issue=2 |pages=253–268 |doi=10.1017/s0043933911000286|s2cid=88353703 }}</ref> or sufficiently long to cause a body weight loss of 25 to 35%,<ref name="Webster, (2003)">{{cite journal |last1=Webster |first1=A.B. |year=2003 |title=Physiology and behavior of the hen during induced moult |journal=Poultry Science |volume=82 |issue=6 |pages=992–1002 |doi=10.1093/ps/82.6.992 |pmid=12817455|doi-access=free }}</ref> or up to 28 days under experimental conditions.<ref name="Molino et al., (2009)">{{cite journal |last1=Molino |first1=A.B. |last2=Garcia |first2=E.A. |last3=Berto |first3=D.A. |last4=Pelícia |first4=K. |last5=Silva |first5=A.P. |last6=Vercese |first6=F. |year=2009 |title=The Effects of Alternative Forced-Molting Methods on The Performance and Egg Quality of Commercial Layers |journal=Brazilian Journal of Poultry Science |volume=11 |issue=2 |pages=109–113 |doi=10.1590/s1516-635x2009000200006|doi-access=free |hdl=11449/14340 |hdl-access=free }}</ref> This stimulates the hen to lose her feathers but also re-invigorates egg-production. Some flocks may be force-moulted several times. In 2003, more than 75% of all flocks were moulted in the US.<ref name="Yousaf and Chaudhry, (2008)">{{cite journal |last1=Yousaf |first1=M. |last2=Chaudhry |first2=A.S. |title=History, changing scenarios and future strategies to induce moulting in laying hens |journal=World's Poultry Science Journal |date=March 1, 2008 |volume=64 |issue=1 |pages=65–75 |doi=10.1017/s0043933907001729 |s2cid=34761543 |url=http://eprint.ncl.ac.uk/file_store/production/56559/452E6892-26EF-40C6-891B-048E9FE17D2E.pdf |access-date=October 23, 2020 |archive-date=November 24, 2020 |archive-url=https://web.archive.org/web/20201124090812/https://eprint.ncl.ac.uk/file_store/production/56559/452E6892-26EF-40C6-891B-048E9FE17D2E.pdf |url-status=live }}</ref>
Another animal welfare concern is the use of [[selective breeding]] to create heavy, large-breasted birds, which can lead to crippling leg disorders and heart failure for some of the birds. Concerns have been raised that companies growing single varieties of birds for eggs or meat are increasing their susceptibility to disease.


=== As pets ===
Some groups who advocate for more humane treatment of chickens, claim that they are intelligent. Dr. Chris Evans of [[Macquarie University]] claims that their range of 20 calls, problem solving skills, use of representational signalling, and the ability to recognize each other by facial features demonstrate the intelligence of chickens.[http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/11/15/nhen15.xml].


Keeping chickens as pets became increasingly popular in the 2000s<ref>{{cite news |title=Some homeowners find chickens all the rage |work=[[Chicago Tribune]] |date=July 27, 2007 |last=Fly |first=Colin |url=https://pqasb.pqarchiver.com/chicagotribune/access/1310840201.html?.dids=1310840201:1310840201&FMT=ABS&FMTS=ABS:FT&type=current&date=Jul+27,+2007&author=Colin+Fly&pub=Chicago+Tribune&desc=Some+homeowners+find+chickens+all+the+rage&pqatl=google }}{{dead link|date=July 2024|bot=medic}}{{cbignore|bot=medic}}</ref> among urban and suburban residents.<ref>{{cite news |title=Cooped up in suburbia |work=[[Boston Globe]] |date=December 16, 2004 |last=Pollack-Fusi |first=Mindy |url=https://www.boston.com/yourlife/home/articles/2004/12/16/cooped_up_in_suburbia/ |access-date=June 4, 2020 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304063550/http://www.boston.com/yourlife/home/articles/2004/12/16/cooped_up_in_suburbia/ |url-status=live }}</ref> Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs. Chickens provide companionship and have individual personalities. While many do not cuddle much, they will eat from one's hand, jump onto one's lap, respond to and follow their handlers, as well as show affection.<ref>{{Cite news|url=https://www.nytimes.com/2020/11/25/magazine/backyard-chickens-empathy.html |archive-url=https://web.archive.org/web/20201125101336/https://www.nytimes.com/2020/11/25/magazine/backyard-chickens-empathy.html |archive-date=November 25, 2020 |url-access=subscription |url-status=live|title = How Caring for Backyard Chickens Stretched My Emotional Muscles|newspaper = The New York Times|date = November 25, 2020|last1 = Kreilkamp|first1 = Ivan}}</ref><ref>{{Cite web|url=https://www.latimes.com/style/pets/la-hm-pets-chickens-20170827-story.html|title=Chickens will become a beloved pet — just like the family dog|last=Boone|first=Lisa|website=[[Los Angeles Times]]|date=August 27, 2017|access-date=April 3, 2019|archive-date=April 2, 2019|archive-url=https://web.archive.org/web/20190402104824/https://www.latimes.com/style/pets/la-hm-pets-chickens-20170827-story.html|url-status=live}}</ref> Chickens are social, inquisitive, intelligent<ref>{{Cite web|last=Barras|first=Colin|title=Despite what you might think, chickens are not stupid|url=https://www.bbc.com/earth/story/20170110-despite-what-you-might-think-chickens-are-not-stupid|archive-url=https://web.archive.org/web/20210605084929/https://www.bbc.com/earth/story/20170110-despite-what-you-might-think-chickens-are-not-stupid|archive-date=June 5, 2021|access-date=September 6, 2020|website=www.bbc.com|language=en}}</ref> birds, and many people find their behaviour entertaining.<ref name='UPC good homes' >{{cite web |url=https://www.upc-online.org/home.html |title=Providing a Good Home for Chickens |author=United Poultry Concerns |access-date=May 4, 2009 |archive-url=https://web.archive.org/web/20090605061816/http://www.upc-online.org/home.html |archive-date=June 5, 2009 |url-status=live }}</ref> Certain breeds, such as [[silkie]]s and many [[Bantam (poultry)|bantam]] varieties, are generally docile and are often recommended as good pets around children with disabilities.<ref>{{cite web |url=https://www.henkeeping.co.uk/henkeeping/choosing-your-chickens/ |website=Clucks and Chooks |title=Choosing Your Chickens |url-status=live |archive-url=https://web.archive.org/web/20090730222405/http://www.henkeeping.co.uk/which.html |archive-date=July 30, 2009}}</ref>
In 2004, 8.9 billion chickens were slaughtered in the United States.<ref>[http://usda.mannlib.cornell.edu/reports/nassr/poultry/ppy-bb/ HTML Redirect<!-- Bot generated title -->]</ref> There is no federal law that regulates the humane treatment of chickens.{{Fact|date=May 2008}}


===Human concerns===
=== Cockfighting ===
====Antibiotics====
Antibiotics have been used on poultry in large quantities since the Forties, when it was found that the byproducts of antibiotic production, fed because the antibiotic-producing mold had a high level of vitamin B12 after the antibiotics were removed, produced higher growth than could be accounted for by the vitamin B12 alone. Eventually it was discovered that the trace amounts of antibiotics remaining in the byproducts accounted for this growth.<ref>Ewing, Poultry Nutrition, 5th ed., 1963, p. 1283.</ref>


{{main|Cockfight}}
The mechanism is apparently the adjustment of intestinal flora, favoring "good" bacteria while suppressing "bad" bacteria, and thus the goal of antibiotics as a growth promoter is the same as for probiotics. Because the antibiotics used are not absorbed by the gut, they do not put antibiotics into the meat or eggs.<ref>Ewing, Poultry Nutrition, 5th ed., 1963, p. 1284.</ref>


[[File:COCK FIGHT.JPG|thumb|A [[cockfight]] in [[Tamil Nadu]], India, 2011 ]]
Antibiotics are used routinely in poultry for this reason, and also to prevent and treat disease. Many contend that this puts humans at risk as bacterial strains develop stronger and stronger resistances.<ref>http://dwb.unl.edu/Teacher/NSF/C10/C10Links/www.sierraclub.org/cafos/toolkit/antibiotic.asp</ref> Critics point out that, after six decades of heavy agricultural use of antibiotics, opponents of antibiotics must still make arguments about theoretical risks, since actual examples are hard to come by. Those antibiotic-resistant strains of human diseases whose origin is known originated in hospitals rather than farms.


A [[cockfight]] is a contest held in a ring called a cockpit between two cocks. Cockfighting is outlawed in many countries as involving [[cruelty to animals]].<ref>{{cite news|author=Raymond Hernandez |url=https://www.nytimes.com/1995/04/11/nyregion/blood-sport-gets-blood-fans-cockfighting-don-t-understand-its-outlaw-status.html?pagewanted=all&src=pm |title=A Blood Sport Gets in the Blood; Fans of Cockfighting Don't Understand Its Outlaw Status |work=The New York Times |location=New York City Metropolitan Area |date=1995-04-11 |access-date=2014-05-10}}</ref> The activity seems to have been practised in the [[Indus Valley civilisation]] from 2500 to 2100 BC.<ref name="Crawford 1990">{{cite book |last=Crawford |first=R. D. |title=''Poultry Breeding and Genetics'' |publisher=[[Elsevier]] |year=1990 |pages=10–11 |isbn=978-0444885579 |ol=2207173M |url=https://openlibrary.org/books/OL2207173M/Poultry_breeding_and_genetics |access-date=February 2, 2024 |archive-date=April 18, 2023 |archive-url=https://web.archive.org/web/20230418123608/https://openlibrary.org/books/OL2207173M/Poultry_breeding_and_genetics |url-status=live }}</ref> In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used for food.<ref name="Lawler Adler 2012">{{cite journal |last1=Lawler |first1=Andrew |last2=Adler |first2=Jerry |title=How the Chicken Conquered the World |journal=Smithsonian Magazine |issue=June 2012 |date=June 2012 |url=http://www.smithsonianmag.com/history/how-the-chicken-conquered-the-world-87583657/ |access-date=February 2, 2024 |archive-date=October 31, 2019 |archive-url=https://web.archive.org/web/20191031040210/https://www.smithsonianmag.com/history/how-the-chicken-conquered-the-world-87583657/ |url-status=live }}</ref>
A proposed bill in the American congress would make the use of antibiotics in animal feed legal only for therapeutic (rather than preventative) use, but it has not been passed yet.<ref>http://www.consumerreports.org/cro/food/animal-feed-and-the-food-supply-105/chicken-arsenic-and-antibiotics/index.htm</ref> However, this may present the risk of slaughtered chickens harboring pathogenic bacteria and passing them on to humans that consume them.


=== In science===
In October 2000, the [[FDA]] discovered that two antibiotics were no longer effective in treating diseases found in factory-farmed chickens; one antibiotic was swiftly pulled from the market, but the other, [[Baytril]] was not. [[Bayer]], the company which produced it, contested the claim and as a result, Baytril remained in use until July of 2005.<ref>[http://www.mindfully.org/Farm/2005/Baytril-Antibiotic-Banned29jul05.htm Baytril: FDA Bans Bayer Antibiotic for Poultry Use RANDY FABI / Reuters 29jul2005<!-- Bot generated title -->]</ref>


Chickens have long been used as [[model organism]]s to study developing embryos. Large numbers of embryos can be provided commercially; fertilized eggs can easily be opened and used to observe the developing embryo. Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development. For instance, many important discoveries in [[limb development]] have been made using chicken embryos, such as the discovery of the [[apical ectodermal ridge]] and the [[zone of polarizing activity]].<ref>{{cite journal |last1=Young |first1=John J. |last2=Tabin |first2=Clifford J. |title=Saunders's framework for understanding limb development as a platform for investigating limb evolution |journal=Developmental Biology |date=September 2017 |volume=429 |issue=2 |pages=401–408 |doi=10.1016/j.ydbio.2016.11.005 |pmid=27840200 |pmc=5426996 }}</ref>
====Arsenic====
Chicken feed can also include [[Roxarsone]], an [[antimicrobial]] drug that also promotes growth. The drug has generated controversy because it contains the element [[arsenic]], which can cause [[cancer]], [[dementia]], and [[neurological]] problems in humans. Yet the arsenic in Roxarsone is not of the type which has been linked to cancer. {{Fact|date=January 2008}} A Consumer Reports study in 2004 reported finding "no detectable arsenic in our samples of muscle" but found "A few of our chicken-liver samples has an amount that according to EPA standards could cause neurological problems in a child who ate 2 ounces of cooked [[liver]] per week or in an adult who ate 5.5 ounces per week." However, the Food and Drug Administration (FDA) is the organization responsible for the regulation of foods in America, and all samples tested were "far less than the... amount allowed in a food product."<ref>http://www.consumerreports.org/cro/food/animal-feed-and-the-food-supply-105/chicken-arsenic-and-antibiotics/index.htm</ref>


The chicken was the first bird species to have its [[genome]] sequenced.<ref>{{cite journal |author=International Chicken Genome Sequencing Consortium |title=Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution |journal=Nature |date=December 9, 2004 |volume=432 |issue=7018 |pages=695–716 |doi=10.1038/nature03154 |pmid=15592404 |bibcode=2004Natur.432..695C |doi-access=free }}</ref> At 1.21 [[Gigabase|Gb]], the chicken genome is similarly sized compared to other birds, but smaller than nearly all mammals: the [[human genome]] is 3.2 [[Gigabase|Gb]].<ref>{{cite journal |last1=Gregory |first1=T. Ryan |title=Synergy between sequence and size in Large-scale genomics |journal=Nature Reviews Genetics |date=September 2005 |volume=6 |issue=9 |pages=699–708 |doi=10.1038/nrg1674|pmid=16151375 |s2cid=24237594 }}</ref> The final gene set contained 26,640 genes (including noncoding genes and [[pseudogene]]s), with a total of 19,119 protein-coding genes, a similar number to the human genome.<ref>{{cite journal |last1=Warren |first1=Wesley C. |last2=Hillier |first2=LaDeana W. |last3=Tomlinson |first3=Chad |last4=Minx |first4=Patrick |last5=Kremitzki |first5=Milinn |last6=Graves |first6=Tina |last7=Markovic |first7=Chris |last8=Bouk |first8=Nathan |last9=Pruitt |first9=Kim D. |last10=Thibaud-Nissen |first10=Francoise |last11=Schneider |first11=Valerie |last12=Mansour |first12=Tamer A. |display-authors=6 |title=A New Chicken Genome Assembly Provides Insight into Avian Genome Structure |journal=G3 |date=January 2017 |volume=7 |issue=1 |pages=109–117 |doi=10.1534/g3.116.035923 |pmid=27852011 |pmc=5217101 }}</ref> In 2006, scientists researching the ancestry of birds switched on a chicken [[recessive gene]], ''talpid2'', and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils.<ref>[https://abcnews.go.com/Technology/story?id=1666805 Scientists Find Chickens Retain Ancient Ability to Grow Teeth] {{Webarchive|url=https://web.archive.org/web/20080620230515/https://abcnews.go.com/Technology/story?id=1666805 |date=June 20, 2008 }} Ammu Kannampilly, [[ABC News (United States)|ABC News]], February 27, 2006. Retrieved October 1, 2007.</ref>
====Growth hormones====
Chickens grow much more rapidly than they once did and some consumers have concluded that this rapid growth is due to the use of hormones in these animals. Some consumers believe that the increasingly earlier onset of [[puberty]] in humans is the result of the liberal use of such hormones. However, hormone use in poultry production is illegal in the United States.<ref>[http://www.fda.gov/cvm/hormones.htm "The Use Of Steroid Hormones For Growth Promotion In Food-Producing Animals"<!-- Bot generated title -->]</ref> Similarly, no chicken meat for sale in Australia is fed hormones.<ref>[http://www.abc.net.au/landline/stories/s543233.htm Landline - 5/05/2002: Challenging food safety myths . Australian Broadcasting Corp<!-- Bot generated title -->]</ref> Furthermore, several scientific studies have documented the fact that chickens grow rapidly because they are bred to do so.<ref>[http://ps.fass.org/cgi/content/abstract/82/10/1509 Carcass composition and yield of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets - Havenstein et al. 82 (10): 1509 - Poultry Science<!-- Bot generated title -->]</ref><ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7877935&dopt=Abstract Carcass composition and yield of 1991 vs 1957 broi...[Poult Sci. 1994&#93; - PubMed Result<!-- Bot generated title -->]</ref> A small producer of natural and organic chickens confirmed this assumption:


=== In culture, folklore, and religion ===
{{cquote|If this were 1948, you might have something to worry about. Using hormones to boost egg production was a brief fad in the [[Forties]], but was abandoned because it didn't work. Using hormones to produce soft-meated roasters was used to some extent in the Forties and Fifties, but the increased growth rates of broilers made the practice irrelevant--the broilers got as big as anyone wanted them to get when they were still young enough to be soft-meated without chemicals.
The only hormone that was ever used in any quantity on poultry (DES) was banned in 1959, after everyone but a few die-hard farmers had given them up as a silly idea. Hormones are now illegal in poultry and eggs. The people who advertise "No hormones" are either woefully ignorant or are indulging in cynical fear-mongering, maybe both.[http://www.plamondon.com/faq_myths.html]|}}


{{Anchor|Crowing|Cockadoodledoo|Cocka-doodle-doo}}
====''E. coli''====
[[Image:Chickenfamily.jpg|thumb|right|200px|A free roaming [[Bantam (chicken)|bantam]] chicken family of [[rooster]], hen and six [[chick]]s as seen on the streets of downtown [[Key West, Florida]]]]


{{main|Cultural references to chickens}}
According to [[Consumer Reports]], "1.1 million or more Americans [are] sickened each year by undercooked, tainted chicken." A [[United States Department of Agriculture|USDA]] study discovered ''[[E. coli]]'' in 99% of supermarket chicken, the result of chicken butchering not being a sterile process. Feces tend to leak from the carcass until the evisceration stage, and the evisceration stage itself gives an opportunity for the interior of the carcass to receive intestinal bacteria. (So does the skin of the carcass, but the skin presents a better barrier to bacteria and reaches higher temperatures during cooking). Before 1950, this was contained largely by not eviscerating the carcass at the time of butchering, deferring this until the time of retail sale or in the home. This gave the intestinal bacteria less opportunity to colonize the edible meat. The development of the "ready-to-cook broiler" in the 1950s added convenience while introducing risk, under the assumption that end-to-end refrigeration and thorough cooking would provide adequate protection. ''E. coli'' can be killed by proper cooking times, but there is still some risk associated with it, and its near-ubiquity in commercially-farmed chicken is troubling to some. Irradiation has been proposed as a means of sterilizing chicken meat after butchering.


Chickens are featured widely in [[folklore]], [[religion]], [[literature]], and popular culture. The chicken is a sacred animal in many cultures and deeply embedded in belief systems and religious practices.<ref name="smithsonianmag.com">{{cite magazine |last1=Adler |first1=Jerry |last2=Lawler |first2=Andrew |date=June 2012 |title=How the Chicken Conquered the World |url=https://www.smithsonianmag.com/history/how-the-chicken-conquered-the-world-87583657/ |magazine=Smithsonian |access-date=24 May 2012 |archive-url=https://web.archive.org/web/20121103193648/http://www.smithsonianmag.com/history-archaeology/How-the-Chicken-Conquered-the-World.html |archive-date=3 November 2012 |url-status=live}}</ref>
====Avian influenza====
Roosters are sometimes used for [[divination]], a practice called alectryomancy. This involves the sacrifice of a sacred rooster, often during a ritual [[cockfight]], used as a form of communication with the gods.<ref>{{cite book |url=https://books.google.com/books?id=vvVPAAAAMAAJ&q=Alectryomancy+cockfight&pg=PA394 |title=Encyclopædia Perthensis; Or Universal Dictionary of the Arts, Sciences, Literature, &c. Intended to Supersede the Use of Other Books of Reference |publisher=John Brown |year=1816 |edition=2nd |volume=1 |page=394 |access-date=February 2, 2024 |archive-date=September 21, 2024 |archive-url=https://web.archive.org/web/20240921105802/https://books.google.com/books?id=vvVPAAAAMAAJ&q=Alectryomancy+cockfight&pg=PA394#v=snippet&q=Alectryomancy%20cockfight&f=false |url-status=live }}</ref> In [[Gabriel García Márquez]]'s Nobel-Prize-winning 1967 novel ''[[One Hundred Years Of Solitude]]'', cockfighting is outlawed in the town of Macondo after the patriarch of the Buendia family murders his cockfighting rival and is haunted by the man's ghost.<ref>{{cite news |title=Love and Immolation in Argentina |url=https://www.washingtonpost.com/archive/entertainment/books/1981/08/16/love-and-immolation-in-argentina/9cf0bdac-cfc3-4198-8824-d89d5e059c55/ |newspaper=[[Washington Post]] |date=16 August 1981 |access-date=February 2, 2024 |archive-date=August 27, 2017 |archive-url=https://web.archive.org/web/20170827142619/https://www.washingtonpost.com/archive/entertainment/books/1981/08/16/love-and-immolation-in-argentina/9cf0bdac-cfc3-4198-8824-d89d5e059c55/ |url-status=live }}</ref> [[Chicken joke]]s have been made at least since ''[[The Knickerbocker]]'' published one in 1847.<ref>''The Knickerbocker, or The New York Monthly'', March 1847, p. 283.</ref> Chickens have been featured in art in farmyard scenes such as [[Adriaen van Utrecht]]'s 1646 ''Turkeys and Chickens'' and [[Walter Osborne]]'s 1885 ''Feeding the Chickens''.<ref>{{cite web |last1=Kellogg |first1=Diane M. |title=Chickens in Art History |url=https://www.paintingworldmag.com/post/chickens-in-art-history |publisher=Painting World Magazine |access-date=2 February 2024 |date=22 May 2020 |archive-date=February 2, 2024 |archive-url=https://web.archive.org/web/20240202161615/https://www.paintingworldmag.com/post/chickens-in-art-history |url-status=dead }}</ref> The [[nursery rhyme]] "[[Cock a doodle doo]]", its chorus line imitating the cockerel's call, was published in ''[[Mother Goose's Melody]]'' in 1765.<ref>{{cite book |last1=Opie |first1=Iona |last2=Opie |first2=Peter |title=The Oxford Dictionary of Nursery Rhymes |publisher=[[Oxford University Press]] |orig-year=1951 |edition=2nd |year=1997 |page=128}}</ref>
{{main|Avian influenza}}
The 2000 animated [[adventure film|adventure]] [[comedy film]] ''[[Chicken Run]]'', directed by [[Peter Lord]] and [[Nick Park]], featured [[Anthropomorphism|anthropomorphic]] chickens with many chicken jokes.<ref>{{cite magazine |last=Corliss |first=Richard |date=2000-12-04 |title=Run, Chicken Run! |language=en-US |magazine=Time |url=https://content.time.com/time/world/article/0,8599,2047283,00.html |access-date=2023-03-23 |issn=0040-781X |archive-date=24 January 2023 |archive-url=https://web.archive.org/web/20230124033415/https://content.time.com/time/world/article/0,8599,2047283,00.html |url-status=live }}</ref><ref>{{Cite web|url=https://catalog.afi.com/Catalog/moviedetails/61096|title=AFI&#124;Catalog|access-date=17 August 2018|archive-date=17 August 2018|archive-url=https://web.archive.org/web/20180817060102/https://catalog.afi.com/Catalog/moviedetails/61096|url-status=live}}</ref><ref>{{Cite web |url=https://www.sfgate.com/movies/amp/Chicken-Recipe-Simply-Divine-Action-comedy-3239861.php|title='Chicken' Recipe Simply Divine / Action comedy blends great story, animation |website=SFGate |date=21 June 2000 |access-date=2 June 2021 |archive-date=2 June 2021 |archive-url=https://web.archive.org/web/20210602214504/https://www.sfgate.com/movies/amp/Chicken-Recipe-Simply-Divine-Action-comedy-3239861.php |url-status=live}}</ref>
There is also a risk that the crowded conditions in many chicken farms will allow [[avian influenza]] to spread quickly. A [[United Nations]] press release states: "Governments, local authorities and international agencies need to take a greatly increased role in combating the role of factory-farming, commerce in live poultry, and wildlife markets which provide ideal conditions for the virus to spread and mutate into a more dangerous form..."<ref>http://www.farmsanctuary.org/newsletter/Avain_flu.htm</ref>


<gallery class=center mode=nolines widths=200 heights=180>
====Efficiency====
File:Terracotta askos (flask) in the form of a rooster MET DP252108 (cropped).jpg|[[Etruscan civilization|Etruscan]] askos in the form of a rooster, 4th century B.C.
Farming of chickens on an industrial scale relies largely on high protein feeds derived from [[soybean]]s; in the European Union the soybean dominates the protein supply for animal feed,<ref>[http://www.fao.org/docrep/007/y5019e/y5019e03.htm#bm03 Protein Sources For The Animal Feed Industry<!-- Bot generated title -->]</ref> and the poultry industry is the largest consumer of such feed.<ref>[http://www.fao.org/docrep/007/y5019e/y5019e03.htm#bm03 Protein Sources For The Animal Feed Industry<!-- Bot generated title -->]</ref> Giving the feed to chickens means the protein reaches humans with a much lower efficiency than through direct consumption of soybean products. Some nutrients, however, are present in chicken but not in the soybean.
File:Rooster and hen, Dong Ho picture, paper - Vietnam National Museum of Fine Arts - Hanoi, Vietnam - DSC05287.JPG|Rooster and hen, [[Đông Hồ painting|Đông Hồ folk woodcut]], Vietnam
File:Feeding the chickens, by Walter Frederick Osborne.jpg|''Feeding the chickens'' by [[Walter Osborne]], 1885
File:Joseph Crawhall - Spanish Cock And Snail.jpg|[[Joseph Crawhall III]], ''Spanish Cock and Snail'', c. 1900
File:Chicken Mask Bali.jpg|Wooden chicken mask, [[Bali]], late 20th century
File:Yoruba Cockfight.jpg|Carved and painted wooden tribal statue of a cock fight, [[Yoruba culture|Yoruba]], West Africa, c. 2000
</gallery>


===Genetic Pollution===
== Notes ==
One other major problem concerns the wild Red Junglefowl. Feral populations of domestic birds may stray across the ranges of the wild Junglefowl species, it has created a concern of [[genetic pollution]]. Wild Junglefowl should have an eclipse plumage but apparently some males lack such a plumage, indicating hybridisation with the domestic chicken. Further confusing the issue of hybrids is that the domestic chicken itself is a hybrid between the Red and Grey Junglefowl. It has even been suggested that pure populations of Red Junglefowl may already be extinct.


{{notelist}}
==Chicken diseases==
[[Image:Chikies 17apr06.jpg|thumb|200px|Baby chicks in a box]]
Chickens are susceptible to several [[parasite]]s, including [[lice]], [[mite]]s, [[tick]]s, [[flea]]s, and [[Roundworm|intestinal worm]]s, as well as other diseases. (Despite the name, they are not affected by [[Chickenpox]]; that is a disease of humans, not chickens.)


== References ==
Some of the common diseases that affect chickens are shown below:
{| class="wikitable"
| style="background: lightgray;" | '''Name'''
| style="background: lightgray;" | '''Common Name'''
| style="background: lightgray;" | '''Caused by'''
|-
|[[Aspergillosis]]
|
|fungi
|-
|[[Avian influenza]]
|bird flu
|virus
|-
|[[Blackhead disease|Histomoniasis]]
|Blackhead disease
|protozoal parasite
|-
|[[Botulism]]
|
|toxin
|-
|[[Cage Layer Fatigue]]
|
|mineral deficiencies, lack of exercise
|-
|[[Coccidiosis]]
|
|parasites
|-
|[[Common cold|Cold]]s
|
|virus
|-
|[http://www.budgie-parakeets.com/cropbound.html Crop Bound]
|
|improper feeding
|-
|[[Dermanyssus gallinae]]
|Red mite
|parasite
|-
|[[Egg bound]]
|
|oversized egg
|-
|[[Erysipelas]]
|
|bacteria
|-
|[[Fatty Liver Hemorrhagic Syndrome]]
|
|high-energy food
|-
|[http://www.michigan.gov/dnr/0,1607,7-153-10370_12150_12220-26650--,00.html Fowl Cholera]
|
|bacteria
|-
|[[Fowl pox]]
|
|virus
|-
|[http://epix.hazard.net/topics/animal/ftyphoid.htm Fowl Typhoid]
|
|bacteria
|-
|[[Gallid herpesvirus 1]]<br>or Infectious Laryngotracheitis
|
|virus
|-
|[[Gapeworm]]
|Syngamus trachea
|worms
|-
|[http://edis.ifas.ufl.edu/PS039 Infectious Bronchitis]
|
|virus
|-
|[[Infectious Bursal Disease]]
|Gumboro
|virus
|-
|[http://www.peafowl.org/ARTICLES/15/ Infectious Coryza]
|
|bacteria
|-
|[[Avian leukosis virus|Lymphoid leukosis]]
|
|Avian leukosis virus
|-
|[[Marek's disease]]
|
|virus
|-
|[[Moniliasis]]
|Yeast Infection<br>or Thrush
|fungi
|-
|[[Mycoplasmas]]
|
|bacteria-like organisms
|-
|[[Newcastle disease]]
|
|virus
|-
|[http://www.thepoultrysite.com/diseaseinfo/101/necrotic-enteritis Necrotic Enteritis]
|
|bacteria
|-
|[[Omphalitis]]
|Mushy chick disease
|umbilical cord stump
|-
|[http://poultryone.com/articles/feedinghens.html Prolapse]
|
|
|-
|[[Psittacosis]]
|
|bacteria
|-
|[[Salmonella|Pullorum]]
|Salmonella
|bacteria
|-
|[[Scaly leg]]
|
|parasites
|-
|[[Squamous cell carcinoma]]
|
|cancer
|-
|[[Tibial dyschondroplasia]]
|
|speed growing
|-
|[[Toxoplasmosis]]
|
|protozoal parasite
|-
|[http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/201500.htm Ulcerative Enteritis]
|
|bacteria
|}


{{reflist}}
==Chickens in religion==
[[Image:Huehner.jpg|thumb|200px|Chickens, [[Indonesia]]]]


== External links ==
In [[Islam]], [[Muhammad|The Messenger of Allah]] said, "When you hear the crowing of cocks, ask for [[Allah]]'s Blessings for (their crowing indicates that) they have seen an [[angel]]. And when you hear the braying of [[donkey]]s, seek Refuge with Allah from [[Satan]] for (their braying indicates) that they have seen a Satan." [[Sahih Al-Bukhari]] Vol. 4, Book 54, Number 522: Narrated Abu Huraira.


{{Commons category|Chickens}}
In [[Indonesia]] the chicken has great significance during the [[Hinduism|Hindu]] [[cremation]] ceremony. A chicken is considered a channel for [[evil spirit]]s which may be present during the ceremony. A chicken is tethered by the [[leg]] and kept present at the ceremony for its duration to ensure that any evil spirits present during the ceremony go into the chicken and not the family members present. The chicken is then taken home and returns to its normal life.
{{Spoken Wikipedia|date=2024-02-22|Chicken Wikipedia.ogg}}
* {{Wikispecies-inline|Gallus gallus domesticus|''Gallus gallus domesticus''}}


{{Chicken}}
In [[ancient Greece]], the chicken was not normally used for sacrifices, perhaps because it was still considered an exotic animal. Because of its valour, the cock is found as an attribute of [[Ares]], [[Heracles]], and [[Athena]]. The alleged last words of [[Socrates]] as he died from [[hemlock]] poisoning, as recounted by [[Plato]], were "[[Crito]], I owe a cock to [[Asclepius]]; will you remember to pay the debt?", signifying that [[death]] was a cure for the illness of life.
{{Poultry}}
{{Taxonbar|from=Q780}}
{{Authority control}}


[[Category:Chickens| ]]
The Greeks believed that even [[lion]]s were afraid of cocks. Several of [[Aesop's Fables]] reference this belief. In the cult of [[Mithras]], the cock was a symbol of the divine light and a guardian against evil.{{Fact|date=February 2007}}
[[Category:Birds described in 1758]]

[[Category:Bird common names]]
In the [[New Testament]], [[Jesus]] prophesied the betrayal by [[Peter]]: "Jesus answered, 'I tell you, Peter, before the rooster crows today, you will deny three times that you know me.'" ([[Gospel of Luke|Luke]] 22:34) Thus it happened ([[Gospel of Luke|Luke]] 22:61), and Peter cried bitterly. This made the cock a symbol for both vigilance and betrayal.
[[Category:Taxa named by Carl Linnaeus]]

[[Category:Articles containing video clips]]
Earlier, Jesus compares himself to a mother hen when talking about [[Jerusalem]]: "O Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you, how often I have longed to gather your children together, as a hen gathers her chicks under her wings, but you were not willing." ([[Gospel of Matthew|Matthew]] 23:37; also Luke 13:34).

In many [[Central Europe]]an [[folk tale]]s, the [[devil]] is believed to flee at the first crowing of a cock.

In traditional [[Orthodox Judaism|Jewish]] practice, a chicken is swung around the head and then slaughtered on the afternoon before [[Yom Kippur]], the Day of Atonement, in a ritual called [[kapparos]]. The sacrifice of the chicken is to receive atonement, for the bird takes on all the person's sins in kapparos. The meat is then donated to the poor. A [[woman]] brings a hen for the ceremony, while a [[man]] brings a rooster. Although not actually a sacrifice in the biblical sense, the death of the chicken reminds the penitent sinner that his or her life is in [[God]]'s hands.

The [[Talmud]] speaks of learning "courtesy toward one's mate" from the rooster. This might refer to the fact that when a rooster finds something good to eat, he calls his hens to eat first.

The chicken is one of the [[Zodiac]] symbols of the [[Chinese calendar]]. Also in [[Chinese religion]], a cooked chicken as a religious offering is usually limited to ancestor veneration and worship of village deities. [[Vegetarian]] deities such as the [[Gautama Buddha|Buddha]] are not one of the recipients of such offerings. Under some observations, an offering of chicken is presented with "serious" prayer (while roasted [[pork]] is offered during a joyous celebration). In [[Confucian]] Chinese [[Wedding]]s, a chicken can be used as a substitute for one who is seriously ill or not available (e.g sudden death) to attend the ceremony. A red [[silk]] scarf is placed on the chicken's head and a close relative of the absent bride/groom holds the chicken so the ceremony may proceed. However, this practice is rare today.

==Chickens in history==
[[Image:Red junglefowl hm.jpg|thumb|left|The Red Junglefowl]]
The first pictures of chickens in Europe are found on [[Corinth, Greece|Corinthian]] [[pottery]] of the 7th century BCE. The poet [[Cratinus]] (mid-5th century BCE, according to the later Greek author [[Athenaeus]]) calls the chicken "the [[Iran|Persia]]n alarm". In [[Aristophanes]]'s comedy ''[[The Birds (play)|The Birds]]'' (414 BCE) a chicken is called "the [[Medes|Median]] bird", which points to an introduction from the East. Pictures of chickens are found on Greek [[red-figure pottery|red figure]] and [[black-figure pottery]].

In ancient Greece, chickens were still rare and were a rather prestigious food for [[Symposium|symposia]]. [[Delos]] seems to have been a centre of chicken breeding.

An early domestication of chickens in [[Southeast Asia]] is probable, since the word for domestic chicken (''*manuk'') is part of the reconstructed [[Proto-Austronesian language]] (see [[Austronesian languages]]). Chickens, together with dogs and [[pig]]s, were the domestic animals of the [[Lapita]] culture, the first [[Neolithic]] culture of [[Oceania]].

Chickens were spread by [[Polynesia]]n seafarers and reached [[Easter Island]] in the 12th century BCE, where they were the only domestic animal, with the possible exception of the [[Polynesian Rat]] (''Rattus exulans''). They were housed in extremely solid chicken coops built from stone. Traveling as cargo on trading boats, they reached the Asian continent via the islands of Indonesia and from there spread west to Europe and western Asia.

The [[ancient Rome|Roman]]s used chickens for oracles, both when flying ("ex avibus") and when feeding ("auspicium ex tripudiis"). The hen ("gallina") gave a favourable omen ("auspicium ratum"), when appearing from the left (Cic.,de Div. ii.26), like the crow and the owl.

For the oracle "ex tripudiis" according to [[Cicero]] (Cic. de Div. ii.34), any bird could be used, but normally only chickens ("pulli") were consulted. The chickens were cared for by the pullarius, who opened their cage and fed them pulses or a special kind of soft cake when an augury was needed. If the chickens stayed in their cage, made noises ("occinerent"), beat their wings or flew away, the omen was bad; if they ate greedily, the omen was good.

In 249 BCE, the Roman general [[Publius Claudius Pulcher]] had his chickens thrown overboard when they refused to feed before the [[battle of Drepana]], saying "If they won't eat, perhaps they will drink." He promptly lost the battle against the [[Carthaginian]]s and 93 Roman ships were sunk. Back in Rome, he was tried for impiety and heavily fined.

In 161 BCE a law was passed in Rome that forbade the consumption of fattened chickens. It was renewed a number of times, but does not seem to have been successful. Fattening chickens with bread soaked in milk was thought to give especially delicious results. The Roman gourmet [[Apicius]] offers 17 recipes for chicken, mainly boiled chicken with a sauce. All parts of the animal are used: the [[recipe]]s include the [[stomach]], liver, [[testicle]]s and even the [[pygostyle]] (the fatty "tail" of the chicken where the tail feathers attach).

The Roman author [[Columella]] gives advice on chicken breeding in his eighth book of his treatise on [[agriculture]]. He identifies Tanagrian, Rhodic, Chalkidic and Median (commonly misidentified as Melian) breeds, which have an impressive appearance, a quarrelsome nature and were used for [[cockfighting]] by the Greeks. For farming, native (Roman) chickens are to be preferred, or a cross between native hens and Greek cocks. Dwarf chickens are nice to watch because of their size but have no other advantages.

Per Columella, the ideal flock consists of 200 birds, which can be supervised by one person if someone is watching for stray animals. White chickens should be avoided as they are not very fertile and are easily caught by eagles or goshawks. One cock should be kept for five hens. In the case of Rhodian and Median cocks that are very heavy and therefore not much inclined to sex, only three hens are kept per cock. The hens of heavy fowls are not much inclined to brood; therefore their eggs are best hatched by normal hens. A hen can hatch no more than 15-23 eggs, depending on the time of year, and supervise no more than 30 hatchlings. Eggs that are long and pointed give more male, rounded eggs mainly female hatchlings.

Per Columella, Chicken coops should face southeast and lie adjacent to the kitchen, as smoke is beneficial for the animals. Coops should consist of three rooms and possess a hearth. Dry dust or ash should be provided for dust-baths.

According to Columella, chicken should be fed on barley groats, small chick-peas, millet and wheat bran, if they are cheap. Wheat itself should be avoided as it is harmful to the birds. Boiled ryegrass (''Lollium'' sp.) and the leaves and seeds of alfalfa (''Medicago sativa'' L.) can be used as well. Grape marc can be used, but only when the hens stop laying eggs, that is, about the middle of November; otherwise eggs are small and few. When feeding grape marc, it should be supplemented with some bran. Hens start to lay eggs after the winter solstice, in warm places around the first of January, in colder areas in the middle of February. Parboiled barley increases their fertility; this should be mixed with alfalfa leaves and seeds, or vetches or millet if alfalfa is not at hand. Free-ranging chickens should receive two cups of barley daily.

Columella advises farmers to slaughter hens that are older than three years, because they no longer produce sufficient eggs.

Capons were produced by burning out their spurs with a hot iron. The wound was treated with potter's chalk.

For the use of poultry and eggs in the kitchens of ancient Rome see [[Roman eating and drinking]].

===Chickens in South America===
An unusual variety of chicken that has its origins in [[South America]] is the [[araucana]]. Araucanas, some of which are tailless and some of which have tufts of feathers around their ears, lay blue-green eggs. It has long been suggested that they predate the arrival of European chickens brought by the [[Spanish colonization of the Americas|Spanish]] and are evidence of [[pre-Columbian]] trans-Pacific contacts between Asian or Pacific Oceanic peoples. particularly the Polynesians, and South America. In 2007, an international team of researchers reported the results of analysis of chicken bones found on the Arauco Peninsula in south central Chile. Radiocarbon dating indicated that the chickens were Pre-Columbian, and DNA analysis showed that they were related to prehistoric populations of chickens in Polynesia.<ref>[http://www.nature.com/news/2007/070604/full/447620b.html DNA reveals how the chicken crossed the sea] Brendan Borrell, Nature, 5 June 2007. Retrieved [[2007-10-01]].</ref> These results appear to confirm that the chickens came from Polynesia and that there were transpacific contacts between Polynesia and South America before Columbus's arrival in the Americas.<ref>A. A. Storey et al, "Radiocarbon and DNA evidence for a pre-Columbian introduction of Polynesian chickens to Chile,"''Proceedings of the National Academy of Sciences of the United States of America'', www.pnas.org/cgi/doi/10.1073/pnas.0703993104; John Noble Wilford, "First Chickens in Americas were Brought from Polynesia, ''New York Times'', June 5, 2007</ref>

==See also==
[[Image:Chooks Sleeping in a Tree.jpg|thumb|right|Unless tamed, chickens will naturally roost in trees.]]
*[[American Poultry Association]]
*[[Alektorphobic]] - someone scared of chickens
*[[List of chicken breeds]]
*[[Chicken coop]]
*[[Symbolic chickens]]
*[[Chicken hypnotism]]
*[[Chicken or the egg]]
*[[Why did the chicken cross the road?]]
*[[Rubber chicken]]
*[[Gamebird hybrids]] - hybrids between chickens, peafowl, guineafowl and pheasants
*[[Chook raffle]] - A type of raffle where the prize is a chicken.
*[[Exploding chicken]]
*[[Chicken fat]]

==References==
<!--<nowiki>
See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the<ref> and </ref> tags, and the template below.
</nowiki>-->
'''Cited'''
{{reflist}}
'''General'''
*{{cite book
| last = Smith
| first = Page
| coauthors = Charles Daniel
| authorlink = Page Smith
| title = ''The Chicken Book''
| publisher = University of Georgia Press
|date=April 2000
| isbn = 082032213X}}

==External links==
{{commons|Gallus gallus|Chicken}}
<!-- ==============================({{NoMoreLinks}})============================== -->
<!-- DO NOT ADD MORE LINKS TO THIS ARTICLE UNLESS THEY CONFORM TO [[WP:EL]]. WIKIPEDIA IS NOT A COLLECTION OF LINKS -->
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[[Category:Chicken|* ]]
[[Category:Junglefowls]]
[[Category:Junglefowls]]
[[Category:United States state birds]]
[[Category:Poultry]]
[[Category:Subspecies]]

[[Category:Cosmopolitan birds]]
[[ar:دجاجة]]
[[Category:National symbols of Kenya]]
[[frp:Genelye]]
[[Category:Heraldic beasts]]
[[ay:Chiwchi]]
[[Category:Austronesian agriculture]]
[[zh-min-nan:Ke]]
[[bo:བྱ་ཏེ་]]
[[bg:Домашна кокошка]]
[[bs:Kokoška]]
[[ca:Gall]]
[[cs:Kur domácí]]
[[da:Høns]]
[[pdc:Hinkel]]
[[de:Haushuhn]]
[[et:Kana]]
[[es:Gallus gallus]]
[[eo:Koko (birdo)]]
[[eu:Oilar]]
[[fa:مرغ]]
[[fr:Gallus gallus domesticus]]
[[gl:Galiña]]
[[ko:닭]]
[[hr:Domaća kokoš]]
[[io:Hano]]
[[id:Ayam]]
[[is:Kjúklingur]]
[[it:Gallo (animale)]]
[[he:תרנגול הבית]]
[[ka:ქათამი]]
[[la:Gallus]]
[[lt:Višta]]
[[hu:Házityúk]]
[[ml:കോഴി]]
[[mr:कोंबडी]]
[[mzn:کرک]]
[[ms:Ayam]]
[[nl:Kip (vogel)]]
[[cr:Pakakuan]]
[[ja:ニワトリ]]
[[no:Høne]]
[[oc:Gallus gallus]]
[[nds:Hohn]]
[[pl:Kura domowa]]
[[pt:Galinha]]
[[qu:Wallpa]]
[[ru:Курица]]
[[simple:Chicken]]
[[sl:Domača kokoš]]
[[sr:Кокошка]]
[[fi:Kana]]
[[sv:Höns]]
[[ta:கோழி]]
[[th:ไก่]]
[[tr:Tavuk]]
[[uk:Кури]]
[[yi:האן]]
[[bat-smg:Vėšta]]
[[zh:鸡]]

Revision as of 08:37, 17 December 2024

Chicken
Male (left) and female (right)
Domesticated
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Galliformes
Family: Phasianidae
Genus: Gallus
Species:
G. g. domesticus
Binomial name
Gallus gallus domesticus
Chicken distribution
Synonyms

Gallus domesticus L.

The chicken (Gallus domesticus) is a large and round short-winged bird, domesticated from the red junglefowl of Southeast Asia around 8,000 years ago. Most chickens are raised for food, providing meat and eggs; others are kept as pets[1] or for cockfighting.

Chickens are common and widespread domestic animals, with a total population of 26.5 billion as of 2023, and an annual production of more than 50 billion birds. A hen bred for laying can produce over 300 eggs per year. There are numerous cultural references to chickens in folklore, religion, and literature.

Nomenclature

Terms for chickens include:

  • Biddy: a chicken, or a newly hatched chicken[2][3]
  • Capon: a castrated or neutered male chicken[a]
  • Chick: a young chicken[4]
  • Chook /ʊk/: a chicken (Australia/New Zealand, informal)[5]
  • Cock: a fertile adult male chicken[6][7]
  • Cockerel: a young male chicken[8]
  • Hen: an adult female chicken[9]
  • Pullet: a young female chicken less than a year old.[10] In the poultry industry, a pullet is a sexually immature chicken less than 22 weeks of age.[11]
  • Rooster: a fertile adult male chicken, especially in North America. Originated in the 18th century, possibly as a euphemism to avoid the sexual connotation of the word cock.[12][13][14]
  • Yardbird: a chicken (southern United States, dialectal)[15]

Chicken can mean a chick, as in William Shakespeare's play Macbeth, where Macduff laments the death of "all my pretty chickens and their dam".[16] The usage is preserved in placenames such as the Hen and Chicken Islands.[17] In older sources, and still often in trade and scientific contexts, chickens as a species are described as common fowl or domestic fowl.[18]

Description

Comb of male
Comb of female, generally smaller

Chickens are relatively large birds, active by day. The body is round, the legs are unfeathered in most breeds, and the wings are short.[19] Wild junglefowl can fly; chickens and their flight muscles are too heavy to allow them to fly more than a short distance.[20] Size and coloration vary widely between breeds.[19] Newly-hatched chicks of both modern and heritage varieties weigh the same, about 37 g (1.3 oz). Modern varieties however grow much faster; by day 35 a Ross 708 broiler may weigh 1.8 kg (4.0 lb) as against the 1.05 kg (2.3 lb) of a heritage chicken of the same age.[21]

Adult chickens of both sexes have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin on either side under their beaks called wattles; combs and wattles are more prominent in males. Some breeds have a mutation that causes extra feathering under the face, giving the appearance of a beard.[22]

Chickens are omnivores.[23] In the wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards, small snakes,[24] and young mice.[25] A chicken may live for 5–10 years, depending on the breed.[26] The world's oldest known chicken lived for 16 years.[27]

Chickens are gregarious, living in flocks, and incubate eggs and raise young communally. Individual chickens dominate others, establishing a pecking order; dominant individuals take priority for access to food and nest sites. The concept of dominance, involving pecking, was described in female chickens by Thorleif Schjelderup-Ebbe in 1921 as the "pecking order".[28][29] Male chickens tend to leap and use their claws in conflicts.[30] Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox.[31]

Crowing (with audio)

A male's crowing is a loud and sometimes shrill call, serving as a territorial signal to other males,[32] and in response to sudden disturbances within their surroundings. Hens cluck loudly after laying an egg and to call their chicks. Chickens give different warning calls to indicate that a predator is approaching from the air or on the ground.[33]

Reproduction and life-cycle

To initiate courting, some roosters may dance in a circle around or near a hen (a circle dance), often lowering the wing which is closest to the hen.[34] The dance triggers a response in the hen[34] and when she responds to his call, the rooster may mount the hen and proceed with the mating. Mating typically involves a sequence in which the male approaches the female and performs a waltzing display. If the female is unreceptive, she runs off; otherwise, she crouches, and the male mounts, treading with both feet on her back. After copulation the male does a tail-bending display.[35]

Sperm transfer occurs by cloacal contact between the male and female, in an action called the 'cloacal kiss'.[36] As with all birds, reproduction is controlled by a neuroendocrine system,[37] the Gonadotropin-Releasing Hormone-I neurons in the hypothalamus. Reproductive hormones including estrogen, progesterone, and gonadotropins (luteinizing hormone and follicle-stimulating hormone) initiate and maintain sexual maturation changes. Reproduction declines with age, thought to be due to a decline in GnRH-I-N.[38]

Newly hatched chicks

Hens often try to lay in nests that already contain eggs and sometimes move eggs from neighbouring nests into their own. A flock thus uses only a few preferred locations, rather than having a different nest for every bird.[39] Under natural conditions, most birds lay only until a clutch is complete; they then incubate all the eggs. This is called "going broody". The hen sits on the nest, fluffing up or pecking defensively if disturbed. She rarely leaves the nest until the eggs have hatched.[40]

Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments. When eggs are placed in a hypoxic environment, chicken embryos from these populations express much more hemoglobin than embryos from other chicken populations. This hemoglobin has a greater affinity for oxygen, binding oxygen more readily.[41]

Fertile chicken eggs hatch at the end of the incubation period, about 21 days; the chick uses its egg tooth to break out of the shell.[34] Hens remain on the nest for about two days after the first chick hatches; during this time the newly hatched chicks feed by absorbing the internal yolk sac.[42] The hen guards her chicks and broods them to keep them warm. She leads them to food and water and calls them towards food. The chicks imprint on the hen and subsequently follow her continually. She continues to care for them until they are several weeks old.[43]

Inbreeding of White Leghorn chickens tends to cause inbreeding depression expressed as reduced egg number and delayed sexual maturity.[44] Strongly inbred Langshan chickens display obvious inbreeding depression in reproduction, particularly for traits such as age when the first egg is laid and egg number.[45]

Origin

Phylogeny

Red junglefowl, the wild ancestor of the chicken

Water or ground-dwelling fowl similar to modern partridges, in the Galliformes, the order of bird that chickens belong to, survived the Cretaceous–Paleogene extinction event that killed all tree-dwelling birds and their dinosaur relatives.[46] Chickens are descended primarily from the red junglefowl (Gallus gallus) and are scientifically classified as the same species.[47] Domesticated chickens freely interbreed with populations of red junglefowl.[47] The domestic chicken has subsequently hybridised with grey junglefowl, Sri Lankan junglefowl and green junglefowl;[48] a gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl (G. sonneratii).[49] It is estimated that chickens share between 71 and 79% of their genome with red junglefowl.[48]

Domestication

Chicken domestication and dispersal;[48] possibility of early arrival in Americas[50][51]

According to one early study, a single domestication event of the red junglefowl in present-day Thailand gave rise to the modern chicken with minor transitions separating the modern breeds.[52] The red junglefowl is well adapted to take advantage of the vast quantities of seed produced during the end of the multi-decade bamboo seeding cycle, to boost its own reproduction.[53] In domesticating the chicken, humans took advantage of the red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply.[54]

Exactly when and where the chicken was domesticated remains controversial. Genomic studies estimate that the chicken was domesticated 8,000 years ago[48] in Southeast Asia and spread to China and India 2,000 to 3,000 years later. Archaeological evidence supports domestic chickens in Southeast Asia well before 6000 BC, China by 6000 BC and India by 2000 BC.[48][55][56] A landmark 2020 Nature study that fully sequenced 863 chickens across the world suggests that all domestic chickens originate from a single domestication event of red junglefowl whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar. These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups. Analysis of the most popular commercial breed shows that the White Leghorn breed possesses a mosaic of divergent ancestries inherited from subspecies of red junglefowl.[57][58][59]

Dispersal

Austronesia

Prehistoric introduction of domesticated chickens into Oceania from the Philippines via Neolithic Austronesian expansion (starting at c. 4000 BP), inferred from genetic markers on ancient and modern chicken DNA (Thomson et al., 2014)[60]

A word for the domestic chicken (*manuk) is part of the reconstructed Proto-Austronesian language, indicating they were domesticated by the Austronesian peoples since ancient times. Chickens, together with dogs and pigs, were carried throughout the entire range of the prehistoric Austronesian maritime migrations to Island Southeast Asia, Micronesia, Island Melanesia, Polynesia, and Madagascar, starting from at least 3000 BC from Taiwan.[60][61][62][63] These chickens might have been introduced during pre-Columbian times to South America via Polynesian seafarers, but evidence for this is still putative.[64]

Americas

The possibility that domestic chickens were in the Americas before Western contact is debated by researchers, but blue-egged chickens, found only in the Americas and Asia, suggest an Asian origin for early American chickens. A lack of data from Thailand, Russia, the Indian subcontinent, Southeast Asia and Sub-Saharan Africa makes it difficult to lay out a clear map of the spread of chickens in these areas; better description and genetic analysis of local breeds threatened by extinction may also help with research into this area.[65] Chicken bones from the Arauco Peninsula in south-central Chile were radiocarbon dated as pre-Columbian, and DNA analysis suggested they were related to prehistoric populations in Polynesia.[50][51] However, further study of the same bones cast doubt on the findings.[66][67]

Eurasia

Chicken remains have been difficult to date, given the small and fragile bird bones; this may account for discrepancies in dates given by different sources. Archaeological evidence is supplemented by mentions in historical texts from the last few centuries BC, and by depictions in prehistoric artworks, such as across Central Asia.[68] Chickens were widespread throughout southern Central Asia by the 4th century BC.[68]

Middle Eastern chicken remains go back to a little earlier than 2000 BC in Syria.[65] Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. During the Hellenistic period (4th–2nd centuries BC), in the southern Levant, chickens began to be widely domesticated for food.[69] The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BC.[70][71]

Breeding increased under the Roman Empire and reduced in the Middle Ages.[65] Genetic sequencing of chicken bones from archaeological sites in Europe revealed that in the High Middle Ages chickens became less aggressive and began to lay eggs earlier in the breeding season.[72]

Africa

Chickens reached Egypt via the Middle East for purposes of cockfighting about 1400 BC and became widely bred in Egypt around 300 BC.[65] Three possible routes of introduction into Africa around the early first millennium AD could have been through the Egyptian Nile Valley, the East Africa Roman-Greek or Indian trade, or from Carthage and the Berbers, across the Sahara. The earliest known remains are from Mali, Nubia, East Coast, and South Africa and date back to the middle of the first millennium AD.[65]

Diseases

8 day old chick with avian influenza

Chickens are susceptible both to parasites such as mites, and to diseases caused by pathogens such as bacteria and viruses. The parasite Dermanyssus gallinae feeds on blood, causing irritation and reducing egg production, and acts as a vector for bacterial diseases such as salmonellosis and spirochaetosis.[73] Viral diseases include avian influenza.[74]

Use by humans

Farming

Chickens are common and widespread domestic animals, with a total population of 23.7 billion as of 2018.[75] More than 50 billion chickens are reared annually as a source of meat and eggs.[76] In the United States alone, more than 8 billion chickens are slaughtered each year for meat,[77] and more than 300 million chickens are reared for egg production.[78] The vast majority of poultry is raised in factory farms. According to the Worldwatch Institute, 74% of the world's poultry meat and 68% of eggs are produced this way.[79] An alternative to intensive poultry farming is free-range farming. Friction between these two main methods has led to long-term issues of ethical consumerism. Opponents of intensive farming argue that it harms the environment, creates human health risks and is inhumane towards sentient animals.[80] Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment.[81] Chickens farmed for meat are called broilers. Broiler breeds typically take less than six weeks to reach slaughter size,[82] some weeks longer for free range and organic broilers.[83]

A commercial chicken house with open sides raising broiler pullets for meat

Chickens farmed primarily for eggs are called layer hens. The UK alone consumes more than 34 million eggs per day.[84] Hens of some breeds can produce over 300 eggs per year; the highest authenticated rate of egg laying is 371 eggs in 364 days.[85] After 12 months of laying, the commercial hen's egg-laying ability declines to the point where the flock is commercially unviable. Hens, particularly from battery cage systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from around seven years to less than two years.[86] In the UK and Europe, laying hens are then slaughtered and used in processed foods, or sold as 'soup hens'.[86] In some other countries, flocks are sometimes force moulted rather than being slaughtered to re-invigorate egg-laying. This involves complete withdrawal of food (and sometimes water) for 7–14 days[87] or sufficiently long to cause a body weight loss of 25 to 35%,[88] or up to 28 days under experimental conditions.[89] This stimulates the hen to lose her feathers but also re-invigorates egg-production. Some flocks may be force-moulted several times. In 2003, more than 75% of all flocks were moulted in the US.[90]

As pets

Keeping chickens as pets became increasingly popular in the 2000s[91] among urban and suburban residents.[92] Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs. Chickens provide companionship and have individual personalities. While many do not cuddle much, they will eat from one's hand, jump onto one's lap, respond to and follow their handlers, as well as show affection.[93][94] Chickens are social, inquisitive, intelligent[95] birds, and many people find their behaviour entertaining.[96] Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities.[97]

Cockfighting

A cockfight in Tamil Nadu, India, 2011

A cockfight is a contest held in a ring called a cockpit between two cocks. Cockfighting is outlawed in many countries as involving cruelty to animals.[98] The activity seems to have been practised in the Indus Valley civilisation from 2500 to 2100 BC.[99] In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used for food.[100]

In science

Chickens have long been used as model organisms to study developing embryos. Large numbers of embryos can be provided commercially; fertilized eggs can easily be opened and used to observe the developing embryo. Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development. For instance, many important discoveries in limb development have been made using chicken embryos, such as the discovery of the apical ectodermal ridge and the zone of polarizing activity.[101]

The chicken was the first bird species to have its genome sequenced.[102] At 1.21 Gb, the chicken genome is similarly sized compared to other birds, but smaller than nearly all mammals: the human genome is 3.2 Gb.[103] The final gene set contained 26,640 genes (including noncoding genes and pseudogenes), with a total of 19,119 protein-coding genes, a similar number to the human genome.[104] In 2006, scientists researching the ancestry of birds switched on a chicken recessive gene, talpid2, and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils.[105]

In culture, folklore, and religion

Chickens are featured widely in folklore, religion, literature, and popular culture. The chicken is a sacred animal in many cultures and deeply embedded in belief systems and religious practices.[106] Roosters are sometimes used for divination, a practice called alectryomancy. This involves the sacrifice of a sacred rooster, often during a ritual cockfight, used as a form of communication with the gods.[107] In Gabriel García Márquez's Nobel-Prize-winning 1967 novel One Hundred Years Of Solitude, cockfighting is outlawed in the town of Macondo after the patriarch of the Buendia family murders his cockfighting rival and is haunted by the man's ghost.[108] Chicken jokes have been made at least since The Knickerbocker published one in 1847.[109] Chickens have been featured in art in farmyard scenes such as Adriaen van Utrecht's 1646 Turkeys and Chickens and Walter Osborne's 1885 Feeding the Chickens.[110] The nursery rhyme "Cock a doodle doo", its chorus line imitating the cockerel's call, was published in Mother Goose's Melody in 1765.[111] The 2000 animated adventure comedy film Chicken Run, directed by Peter Lord and Nick Park, featured anthropomorphic chickens with many chicken jokes.[112][113][114]

Notes

  1. ^ The surgical and chemical castration of chickens is now illegal in some parts of the world.

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