61-476: The megapodes , also known as incubator birds or mound-builders , are stocky, medium-large, chicken -like birds with small heads and large feet in the family Megapodiidae . Their name literally means "large foot" and is a reference to the heavy legs and feet typical of these terrestrial birds. All are browsers , and all except the malleefowl occupy wooded habitats. Most are brown or black in color. Megapodes are superprecocial , hatching from their eggs in
122-414: A predator is approaching from the air or on the ground. 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. The dance triggers a response in the hen 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
183-505: A New Zealand territory and the main island of the Kermadec Islands , may also have once had a species of megapode, based on settler accounts. Megapodes are mainly solitary birds that do not incubate their eggs with their body heat as other birds do, but bury them. Their eggs are unusual in having a large yolk, making up 50–70% of the egg weight. The birds are best known for building massive nest mounds of decaying vegetation, which
244-472: A feature that has revealed the sometimes shallow site of fossils. Prior to 2024, reconstructions of the skull of Genyornis were primarily based on those of its closest relatives, due to the heavily damaged nature of the holotype. However, a 2024 study on the skull morphology of Genyornis , incorporating a recently-discovered well-preserved skull, found the physical appearance of the head of Genyornis to be much more different than previously believed. Namely,
305-467: A few preferred locations, rather than having a different nest for every bird. 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. Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in
366-421: 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. Fertile chicken eggs hatch at the end of the incubation period, about 21 days; the chick uses its egg tooth to break out of
427-404: A result of getting stuck in the mud of the drying lake bed as the water receded. Eventually, when the lake dried, the population was left without their main source of water and subsequently died out. A 2024 study of the skull morphology of Genyornis found apparent adaptations to feeding on aquatic plants, making them closely tied to freshwater habitats. A reliance on these habitats may have made
488-651: A sacred rooster, often during a ritual cockfight , used as a form of communication with the gods. 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. Chicken jokes have been made at least since The Knickerbocker published one in 1847. 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
549-427: A short distance. Size and coloration vary widely between breeds. 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. Chickens are omnivores . In
610-461: A short period—too short for it to be plausibly explained by climate variability . The authors considered this to be a very good indication that the entire mass extinction event in Australia was due to human activity, rather than climate change. A 2015 study collected egg shell fragments of Genyornis from around 200 sites that show burn marks. Analysis of amino acids in the egg shells showed
671-401: 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. 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. In domesticating the chicken, humans took advantage of
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#1732793689685732-407: A thermal gradient consistent with the egg being placed on an ember fire. The egg shells were dated to between 53.9 and 43.4 thousand years BP , suggesting that humans were collecting and cooking Genyornis eggs in the thousands of years before their extinction. A later study suggested that the eggs actually belonged to the giant malleefowl , a species of extinct megapode . A 2022 study examined
793-521: 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. Terms for chickens include: 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". The usage
854-564: A vector for bacterial diseases such as salmonellosis and spirochaetosis . Viral diseases include avian influenza . Chickens are common and widespread domestic animals, with a total population of 23.7 billion as of 2018 . More than 50 billion chickens are reared annually as a source of meat and eggs. In the United States alone, more than 8 billion chickens are slaughtered each year for meat, and more than 300 million chickens are reared for egg production. The vast majority of poultry
915-617: Is a contest held in a ring called a cockpit between two cocks. Cockfighting is outlawed in many countries as involving cruelty to animals . The activity seems to have been practised in the Indus Valley civilisation from 2500 to 2100 BC. In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used for food. 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
976-498: Is an extinct species of large, flightless bird that lived in Australia during the Pleistocene Epoch until around 50,000 years ago. Over two metres in height, they were likely herbivorous . Many other species of Australian megafauna became extinct in Australia around that time, coinciding with the arrival of humans. It is the last known member of the extinct flightless bird family Dromornithidae which had been part of
1037-592: Is inhumane towards sentient animals . 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. Chickens farmed for meat are called broilers . Broiler breeds typically take less than six weeks to reach slaughter size, some weeks longer for free range and organic broilers. Chickens farmed primarily for eggs are called layer hens. The UK alone consumes more than 34 million eggs per day. Hens of some breeds can produce over 300 eggs per year;
1098-811: Is made by the individual species of megapode. Megapode chicks do not have an egg tooth ; they use their powerful claws to break out of the egg, and then tunnel their way up to the surface of the mound, lying on their backs and scratching at the sand and vegetable matter. Similar to other superprecocial birds, they hatch fully feathered and active, already able to fly and live independently from their parents. In megapodes superprecociality apparently evolved secondarily from brooding and at least loose parental care as more typical in Galliformes. Eggs previously assigned to Genyornis have been reassigned to giant megapode species. Some dietary and chronological data previously assigned to dromornithids may instead be assigned to
1159-510: Is preserved in placenames such as the Hen and Chicken Islands . In older sources, and still often in trade and scientific contexts, chickens as a species are described as common fowl or domestic fowl . Chickens are relatively large birds , active by day . The body is round, the legs are unfeathered in most breeds, and the wings are short. Wild junglefowl can fly ; chickens and their flight muscles are too heavy to allow them to fly more than
1220-477: 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. 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
1281-524: Is supplemented by mentions in historical texts from the last few centuries BC, and by depictions in prehistoric artworks, such as across Central Asia. Chickens were widespread throughout southern Central Asia by the 4th century BC. Middle Eastern chicken remains go back to a little earlier than 2000 BC in Syria . Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. During
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#17327936896851342-553: 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. However, further study of the same bones cast doubt on the findings. 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
1403-623: 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. 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
1464-631: The Hellenistic period (4th–2nd centuries BC), in the southern Levant , chickens began to be widely domesticated for food. The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BC. Breeding increased under the Roman Empire and reduced in the Middle Ages . Genetic sequencing of chicken bones from archaeological sites in Europe revealed that in
1525-788: The High Middle Ages chickens became less aggressive and began to lay eggs earlier in the breeding season. Chickens reached Egypt via the Middle East for purposes of cockfighting about 1400 BC and became widely bred in Egypt around 300 BC. 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
1586-463: The Pleistocene Epoch. Genyornis newtoni is the only species of dromornithid known to have existed during the Pleistocene. Two main theories propose a cause for megafauna extinction - human impact and changing climate. A study has been performed in which more than 700 Genyornis eggshell fragments were dated. Through this, it was determined that Genyornis declined and became extinct over
1647-774: The Pleistocene in Northern Africa , the Arabian Peninsula , Southwestern and Northern Asia , and present-day India and China , though they were unable to determine to what extent humans interacted with Genyornis . A 2021 study found that, if Genyornis eggs were being consumed at similar rates to the eggs of the emu and the Australian brushturkey , then Genyornis would have become extinct at far lower rates of total consumption than these still-extant birds. In May 2010, archaeologists announced
1708-575: The clade are the species of Alectura and Talegalla . The smallest are the Micronesian scrubfowl ( Megapodius laperouse ) and the Moluccan scrubfowl ( Eulipoa wallacei ). They have small heads, short beaks, and rounded and large wings. Their flying abilities vary within the clade. They present the hallux at the same level of the other toes just like the species of the clade Cracidae . The other Galliformes have their halluces raised above
1769-618: 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. Chicken bones from
1830-533: 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. 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
1891-722: The Chickens . The nursery rhyme " Cock a doodle doo ", its chorus line imitating the cockerel's call, was published in Mother Goose's Melody in 1765. The 2000 animated adventure comedy film Chicken Run , directed by Peter Lord and Nick Park , featured anthropomorphic chickens with many chicken jokes. Genyornis Genyornis newtoni , also known as the Newton's mihirung , Newton's thunder bird or mihirung paringmal (meaning "giant bird" in Tjapwuring ),
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1952-482: The UK and Europe, laying hens are then slaughtered and used in processed foods, or sold as 'soup hens'. 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 or sufficiently long to cause a body weight loss of 25 to 35%, or up to 28 days under experimental conditions. This stimulates
2013-547: The bill was found to be much more goose -like, with a raised triangular casque . This goose-like bill differed from even other mihirungs, and may have been a specialization for feeding on aquatic vegetation. Other potential adaptations to an aquatic feeding style may have allowed for protection of the ears and throat when submerging their heads in water. This mihirung has been found at sites in South Australia, New South Wales, Queensland and Western Australia, dating to
2074-414: The bird is thought to have gone extinct, and it could not be morphologically distinguished from depictions of other birds. In a 2022 study, fossil evidence suggests that the population of Genyornis at Lake Callabonna died around 50,000 years ago, as the lake dried up as the climate changed and became drier. The birds recovered from the site seemed to have been particularly prone to osteomyelitis , as
2135-425: The chicken genome is similarly sized compared to other birds, but smaller than nearly all mammals: the human genome is 3.2 Gb . 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. In 2006, scientists researching the ancestry of birds switched on a chicken recessive gene , talpid2 , and found that
2196-545: The crania emerged from the site. The paper reviewed previously described fossil remains of "struthious [ ostrich -like] birds in Australia", which had either been assigned to the ancient emus of Dromaius or the only described species of Dromornis , D. australis Owen. A letter from George Hurst concerning the discovery of a partial skeleton of the species alerted Stirling to its existence in 1893. The placement of this dromornithid species may be summarised as: Dromornithidae (8 species in 4 genera) Genyornis newtoni
2257-446: 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 . The chicken was the first bird species to have its genome sequenced. At 1.21 Gb ,
2318-406: The embryo jaws initiated formation of teeth, like those found in ancient bird fossils. 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. Roosters are sometimes used for divination , a practice called alectryomancy. This involves the sacrifice of
2379-425: 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 . These chickens might have been introduced during pre-Columbian times to South America via Polynesian seafarers, but evidence for this is still putative. The possibility that domestic chickens were in
2440-603: The fauna of the Australian continent for over 30 million years. They are not closely related to ratites such as emus , and their closest living relatives are thought to be fowl . The species was first described in 1896 by Edward Charles Stirling and A. H. C. Zeitz, the authors giving the epithet newtoni for the Cambridge professor Alfred Newton . The name of the genus is derived from the ancient Greek γένυς ( génus ) 'jaw; chin' and ὄρνις ( órnis ) 'bird', because of
2501-417: 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. Sperm transfer occurs by cloacal contact between the male and female, in an action called the 'cloacal kiss'. As with all birds, reproduction is controlled by a neuroendocrine system,
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2562-526: The first egg is laid and egg number. 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. Chickens are descended primarily from the red junglefowl ( Gallus gallus ) and are scientifically classified as
2623-843: The giant megapodes. Megapodes share some similarities to the extinct enantiornithes in terms of their superprecocial life cycle, though also several differences. The more than 20 living species are placed in seven genera. Although the evolutionary relationships between the Megapodiidae are especially uncertain, the morphological groups are clear: Macrocephalon – maleo Eulipoa – Moluccan megapode Megapodius – scrubfowl (12 species) Leipoa – malleefowl Talegalla – brushturkeys (3 species) Alectura – Australian brushturkey Aepypodius – brushturkeys (2 species) In their native Oceania , indigenous peoples protect their nesting sites, as their eggs are considered to be delicacies. Their eggs are about twice
2684-952: 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. Keeping chickens as pets became increasingly popular in the 2000s among urban and suburban residents. 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. Chickens are social, inquisitive, intelligent birds, and many people find their behaviour entertaining. Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities. A cockfight
2745-418: The highest authenticated rate of egg laying is 371 eggs in 364 days. 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. In
2806-724: The level of the front toes. Megapodes are found in the broader Australasian region, including islands in the western Pacific , Australia , New Guinea , and the islands of Indonesia east of the Wallace Line , but also the Andaman and Nicobar Islands in the Bay of Bengal . The distribution of the family has contracted in the Pacific with the arrival of humans, and a number of island groups such as Fiji , Tonga , and New Caledonia have lost many or all of their species. Raoul Island ,
2867-456: The male attends, adding or removing litter to regulate the internal heat while the eggs develop. However, some bury their eggs in other ways; there are burrow-nesters which use geothermal heat, and others which simply rely on the heat of the sun warming the sand. Some species vary their incubation strategy depending on the local environment. Although the Australian brushturkey was thought to exhibit temperature-dependent sex determination , this
2928-567: The most mature condition of any bird. They hatch with open eyes, bodily coordination and strength, full wing feathers, and downy body feathers, and are able to run, pursue prey and, in some species, fly on the day they hatch. From the Greek μέγας ( mégas = great ) and πούς , ( poús = foot ). Megapodes are medium-sized to large terrestrial birds with large legs and feet with sharp claws. Megapodes are of three kinds: scrub fowl, brush turkeys, and mallee fowl or lowan. The largest members of
2989-537: The most popular commercial breed shows that the White Leghorn breed possesses a mosaic of divergent ancestries inherited from subspecies of red junglefowl. 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
3050-415: The protein sequences of these unidentified eggshells and, through phylogenetic analysis, concluded that the lineage that produced these eggs diverged prior to the emergence of megapodes, supporting the previous implication that the eggs in question were produced by Genyornis. The authors noted that the exploitation of Genyornis eggs appears to mirror that of earlier human usage of ostrich eggs throughout
3111-609: The red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply. Exactly when and where the chicken was domesticated remains controversial. Genomic studies estimate that the chicken was domesticated 8,000 years ago 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. A landmark 2020 Nature study that fully sequenced 863 chickens across
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#17327936896853172-560: The rediscovery of an Aboriginal rock art painting, possibly 40,000 years old, at the Nawarla Gabarnmung rock art site in the Northern Territory , that they suggested depicts two Genyornis individuals. In 2011, late survival of Genyornis in temperate south west Victoria was suggested, based on Aboriginal traditions. A later study suggested that the painting could not be more than 14,000 years old, long after
3233-541: The relatively large size of the lower mandible. The specimen is a left femur . It was found at Lake Callabonna in South Australia. The excavation was undertaken and described by Zietz. A description of the excavation was reported in Nature which had also unearthed material recognised as marsupials. Numerous fragments of avian fossils were noticed in the clay surrounding the removal of diprotodont fossils, then largely complete specimens including crucial evidence of
3294-462: The same species. Domesticated chickens freely interbreed with populations of red junglefowl. The domestic chicken has subsequently hybridised with grey junglefowl , Sri Lankan junglefowl and green junglefowl ; a gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl ( G. sonneratii ). It is estimated that chickens share between 71 and 79% of their genome with red junglefowl. According to one early study,
3355-703: The shell. 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 . 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. Inbreeding of White Leghorn chickens tends to cause inbreeding depression expressed as reduced egg number and delayed sexual maturity. Strongly inbred Langshan chickens display obvious inbreeding depression in reproduction, particularly for traits such as age when
3416-462: The size of chicken eggs and the yolks are roughly four times as massive. Chicken 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 or for cockfighting . Chickens are common and widespread domestic animals, with
3477-530: The wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards , small snakes, and young mice . A chicken may live for 5–10 years, depending on the breed . The world's oldest known chicken lived for 16 years. 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,
3538-404: 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
3599-630: Was a medium-sized dromornithid with a robust body, measuring up to 2.15 metres (7.1 ft) tall and weighing around 250–350 kilograms (550–770 lb), though body mass estimation may vary based on different methods. While larger than Ilbandornis , it did not attain the height and weight of Dromornis stirtoni or Dromornis planei . The fossils of the species have been found remaining in articulation, and no other dromornithid species has been discovered in this state. The remains of eggs have also been attributed to this species. Gastroliths belonging to these animals have been found alongside their remains,
3660-553: Was described in female chickens by Thorleif Schjelderup-Ebbe in 1921 as the "pecking order". Male chickens tend to leap and use their claws in conflicts. Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox. A male's crowing is a loud and sometimes shrill call, serving as a territorial signal to other males, 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
3721-400: Was later proven false; temperature does, however, affect embryo mortality and resulting offspring sex ratios. The nonsocial nature of their incubation raises questions as to how the hatchlings come to recognise other members of their species, which is due to imprinting in other members of the order Galliformes . Research suggests an instinctive visual recognition of specific movement patterns
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