| Chicken | |
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| A rooster or cock (left) and hen (right) | |
The chicken (Gallus gallus domesticus) is a type of domesticated fowl, a subspecies of the red junglefowl. It is one of the most common and widespread domestic animals, with a total population of more than 19 billion as of 2011. There are more chickens in the world than any other bird.[1] Humans keep chickens primarily as a source of food (consuming both their meat and eggs) and, more rarely, as pets. Originally raised for cockfighting or for special ceremonies, chickens were not kept for food until the Hellenistic period (fourth–second centuries BCE).[2][3]
Genetic studies have pointed to multiple maternal origins in Southeast Asia, East Asia,[4] and South Asia, but with the clade found in the Americas, Europe, the Middle East and Africa originating in the Indian subcontinent. From India, the domesticated chicken was imported to Lydia in western Asia Minor, and to Greece by the fifth century BC.[5] Fowl had been known in Egypt since the mid-15th century BC, with the "bird that gives birth every day" having come to Egypt from the land between Syriaand Shinar, Babylonia, according to the annals of Thutmose III.[6][7][8]
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"Chicken" originally referred to young domestic fowl.[12] 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 British public house 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). The word "chicken" is sometimes erroneously construed to mean females exclusively, despite the term "hen" for females being in wide circulation, and the term “rooster” for males being that most commonly used.
In the Deep South of the United States, chickens are also referred to by the slang term yardbird.[13]
General biology and habitat
Chickens are omnivores.[14] In the wild, they often scratch at the soil to search for seeds, insects and even animals as large as lizards, small snakes or young mice.[15]
The average chicken may live for five to ten years, depending on the breed.[16]The world's oldest known chicken was a hen which died of heart failure at the age of 16 years according to the Guinness World Records.[17]
Roosters can usually be differentiated from hens by their striking plumage of long flowing tails and shiny, pointed feathers on their necks (hackles) and backs (saddle), which are typically of brighter, bolder colours than those of females of the same breed.
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Social behaviour
Chickens are gregarious birds and live together in flocks. They have a communal approach to the 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 food access 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 fighting and injury.[18] When a rooster finds food, he may call other chickens to eat first. He does this by clucking in a high pitch as well as picking up and dropping the food. This behaviour may also be observed in mother hens to call their chicks and encourage them to eat.
A rooster's crowing is a loud and sometimes shrill call and sends a territorial signal to other roosters.[19] However, roosters may also crow in response to sudden disturbances within their surroundings. Hens cluck loudly after laying an egg, and also to call their chicks. Chickens also give different warning calls when they sense a predator approaching from the air or on the ground.[20]
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The domestic chicken is descended primarily from the red junglefowl (Gallus gallus) and is scientifically classified as the same species.[26] As such, it can and does freely interbreed with populations of red junglefowl.[26] Recent genetic analysis has revealed that at least the gene for yellow skin was incorporated into domestic birds through hybridization with the grey junglefowl (G. sonneratii).[27]
The traditional view is that chickens were first domesticated for cockfighting in Asia, Africa, and Europe.[28] In the last decade, there have been a number of genetic studies to clarify the origins. According to one early study, a single domestication event which took place in what now is the country of Thailand gave rise to the modern chicken with minor transitions separating the modern breeds.[29] However, that study was later found to be based on incomplete data, and recent studies point to multiple maternal origins, with the clade found in the Americas, Europe, Middle East, and Africa, originating from the Indian subcontinent, where a large number of unique haplotypes occur.[30][31] It is postulated that the red junglefowl, known as the bamboo fowl in many Southeast Asian languages, is a special bird well-adapted to take advantage of the large amounts of fruits that are produced during the end of the 50-year bamboo seeding cycle, to boost its own reproduction.[32] In domesticating the chicken, humans took advantage of this predisposition for prolific reproduction of the red junglefowl when exposed to large amounts of food.[33]
It has been claimed (based on paleoclimatic assumptions) that chickens were domesticated in Southern China in 6000 BC.[34] However, a recent study[35] raises doubts as to whether those birds were the ancestors of chickens today. Instead, the origin could be the Harappan culture of the Indus Valley. Eventually, the chicken moved to the Tarim basin of central Asia. The chicken reached Europe (Romania, Turkey, Greece, Ukraine) about 3000 BC.[36] Introduction into Western Europe came far later, about the 1st millennium BC. Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. Breeding increased under the Roman Empire, and was reduced in the Middle Ages.[36] 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.[37]
Middle East traces of chicken go back to a little earlier than 2000 BC, in Syria; chickens went southward only in the 1st millennium BC. They reached Egypt for purposes of cockfighting about 1400 BC, and became widely bred only in PtolemaicEgypt (about 300 BC).[36] Little is known about the chicken's introduction into Africa. It was during the Hellenistic period(fourth–second centuries B.C.E.), in the Southern Levant, that chickens began widely to be domesticated for food.[38]. This change occurred at least 100 years before domestication of chickens spread to Europe.
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Chickens are social, inquisitive, intelligent birds, and many find their behaviour entertaining.[57] Certain breeds, such as Silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities.[58]
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