Chicken

The chicken (Gallus gallus domesticus) is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult male bird, and a younger male may be called a cockerel. A male that has been castrated is a capon. An adult female bird is called a hen and a sexually immature female is called a pullet. Humans now keep chickens primarily as a source of food (consuming both their meat and eggs) and as pets. Traditionally they were also bred for cockfighting, which is still practiced in some places. The chicken domesticated for its meat are Broilers and for its eggs are Layers.

Chickens are one of the most common and widespread domestic animals, with a total population of 23.7 billion as of 2018, up from more than 19 billion in 2011. There are more chickens in the world than any other bird. There are numerous cultural references to chickens – in myth, folklore and religion, and in language and literature.

Terminology
An adult male is a called a cock or (in the United States) a rooster and an adult female is called a hen.

Other terms are:

• Biddy: a newly hatched chicken
• Capon: a castrated or neutered male chicken
• Chick: a young chicken
• Chook /tʃʊk/: a chicken (Australia/New Zealand, informal)
• Cockerel: a young male chicken less than a year old
• Dunghill fowl: a chicken with mixed parentage from different domestic varieties.
• Pullet: a young female chicken less than a year old. In the poultry industry, a pullet is a sexually immature chicken less than 22 weeks of age.
• Yardbird: a chicken (southern United States, dialectal)

Chicken may also mean a chick (see for example Hen and Chicken Islands). In fact, chicken was originally a term only for an immature, or at least young, bird. In older sources, chicken as a species were typically referred to as common fowl or domestic fowl.

In Australian vernacular English the word chook provides the generic term for the species (e.g. "a cooked chook" or "she keeps chooks"); which enables chicken to commonly retain its original sense of a young or recently hatched bird. Chick is then rarely used to mean chicken, but is mainly used in Merriam-Webster's "Sense 1b" viz. the young of any bird

General biology and habitat
Chickens are omnivores. In the wild, they often scratch at the soil to search for seeds, insects, and even animals as large as lizards, small snakes, or sometimes young mice.

The average chicken may live for 5–10 years, depending on the breed. The world's oldest known chicken lived 16 years according to Guinness World Records.

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. However, in some breeds, such as the Sebright chicken, the rooster has only slightly pointed neck feathers, the same colour as the hen's. The identification can be made by looking at the comb, or eventually from the development of spurs 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 comb, or cockscomb, and hanging flaps of skin either side under their beaks called wattles. Collectively, these and other fleshy protuberances on the head and throat are called caruncles. Both the adult male and female have wattles and combs, but in most breeds these are more prominent in males. A 'muff' or 'beard' is a mutation found in several chicken breeds which causes extra feathering under the chicken's face, giving the appearance of a beard.

Domestic chickens are not capable of long-distance flight, although lighter chickens are generally capable of flying for short distances, such as over fences or into trees (where they would naturally roost). Chickens may occasionally fly briefly to explore their surroundings, but generally do so only to flee perceived danger.

Use by humans
Farming
A former battery hen, five days after release. Note the pale comb – the comb may be an indicator of health or vigor.

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 are raised in factory farms. According to the Worldwatch Institute, 74 percent of the world's poultry meat and 68 percent 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 is inhumane. Advocates of intensive farming say that their highly efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in state-of-the-art environmentally controlled facilities.

Reared for meat
Chickens farmed for meat are called broilers. Chickens will naturally live for six or more years, but broiler breeds typically take less than six weeks to reach slaughter size. A free range or organic broiler will usually be slaughtered at about 14 weeks of age.

Reared for eggs
Chickens farmed primarily for eggs are called layer hens. In total, the UK alone consumes more than 34 million eggs per day. Some hen breeds can produce over 300 eggs per year, with "the highest authenticated rate of egg laying being 371 eggs in 364 days". After 12 months of laying, the commercial hen's egg-laying ability starts to decline 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 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 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.
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