Chicken

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. Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development. A cockfight is a contest held in a ring called a cockpit between two cocks. Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities. Chickens are social, inquisitive, intelligent birds, and many people find their behaviour entertaining. 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.

Africa

Chickens are gregarious, living in flocks, and incubate eggs and raise young communally. The body is round, the legs are unfeathered in most breeds, and the wings are short. Chicken can mean a chick, and this was historically the meaning of the word chicken, as in William Shakespeare’s play Macbeth, where Macduff laments the death of “all my pretty chickens and their dam”. As of 2023, the global chicken population exceeds 26.5 billion, with more than 50 billion birds produced annually for consumption. It was first domesticated around 8,000 years ago and is one of the most common and widespread domesticated animals in the world.

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. 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 khela 88 Asia, suggest an Asian origin for early American chickens. Analysis of the most popular commercial breed shows that the White Leghorn breed possesses a mosaic of divergent ancestries inherited from different subspecies of red junglefowl. Archaeological evidence appeared to support domestic chickens in Southeast Asia well before 6000 BC, China by 6000 BC and India by 2000 BC.

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 sits on the nest, fluffing up or pecking defensively if disturbed. A flock thus uses only a few preferred locations, rather than having a different nest for every bird. Reproduction declines with age, thought to be due to a decline in GnRH-I-N.

Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. These chickens may have been introduced during pre-Columbian times to South America via Polynesian seafarers, but this is disputed. Skeletons of birds in the Gallus genus were used as grave goods at the site, confirming domestication. The chicks imprint on the hen and subsequently follow her continually. 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.

If the female is unreceptive, she runs off; otherwise, she crouches, and the male mounts, treading with both feet on her back. Mating typically involves a sequence in which the male approaches the female and performs a waltzing display. 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. 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. Chickens give different warning calls to indicate that a predator is approaching from the air or on the ground. 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.

Domestication and economic production

• Although many taxonomists and ornithologists consider it as a domesticated form of the wild red jungle fowl, some classify it as a subspecies of the red jungle fowl (i.e., G. gallus domesticus), whereas others, including the U.S.
• Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development.
• There is some debate about what the chicken’s scientific name should be.
• The chicken is perhaps the most widely domesticated fowl, raised worldwide for its meat and eggs.
• Farmers have developed numerous breeds and varieties to fulfill commercial requirements.

For most of that period, chickens were a common part of the livestock complement of farms and ranches throughout Eurasia and Africa. Chicken domestication likely occurred more than once in Southeast Asia and possibly India over the most recent 7,400 years, and the first domestications may have been for religious reasons or for the raising of fighting birds. Each flock of chickens develops a social hierarchy that determines access to food, nesting sites, mates, and other resources. At about six months, males produce viable sperm, and females produce viable eggs. Despite the chicken’s close relationship with the red jungle fowl, there is evidence that the gray jungle fowl (G. sonneratii) of southern India and other jungle fowl species, also members of Gallus, may have contributed to the bird’s ancestry.

Newly hatched chicks of both modern and heritage varieties weigh the same, about 37 g (1.3 oz). While the origin is Germanic, it is unclear exactly where the word came from, although it could ultimately have come from an imitation of the sound a chicken makes. The word chicken comes from Old English cicen (pronounced essentially the same as in Modern English).