Chicken, (Gallus gallus), one of over 60 medium-sized poultry breeds descended primarily from India’s wild red jungle fowl (Gallus gallus, Phasianidae family, order Galliformes). The chicken is perhaps the most widely domesticated fowl, raised for its meat and eggs worldwide.
Despite the close relationship between the chicken and the red jungle fowl, there is evidence that southern India’s gray jungle fowl (G. sonneratii) and other jungle fowl species, also Gallus members, may have contributed to the bird’s ancestry. There is a bit of controversy about what the scientific name of the chicken will be.
While it is regarded by many taxonomists and ornithologists as a domesticated form of wild red jungle fowl, some identify it as a subspecies of the red jungle, while others, including the United States, do. Agriculture department identify bird as G. Household.
History of the domestic bird called chicken
Chickens look squatty and rounded. They are less than 70 cm (27.6 inches) tall, and on average weigh about 2.6 kg (5.7 pounds). Males (called roosters or cocks) and females (hens) are known for their fleshy combs, lobed wattles hanging under the bill, and high-arched tails.
Chickens breed in the months of spring and summer. The long periods of daylight that occur during the warmer months promote egg-laying; however, artificial lights installed in chicken coops can cause a hen’s response to laying eggs throughout the year.
The time between ovulation and egg-laying is about 23–26 hours. Subsequent ovulations may occur within one hour of the laying of the previous egg, allowing some hens to produce as many as 300 eggs a year.
Fertilized embryos develop rapidly, and about 21 days later, the chicks hatch. Chicks are born coated in down, but they mature easily, and after four to five weeks, they are completely feathered.
The males produce viable sperm at around six months, and the females produce viable eggs. Members of free-ranging flocks that live under the best conditions for six to eight years, but the majority of chickens used in the poultry industry serve as egg layers for two to three years before being slaughtered for their meat, most of which is used in pet food. Chickens are known to live in captivity for up to 30 years.
The European Social Hierarchy of Chicken
Each chickens flock develops a social hierarchy that determines food access, nesting sites, mates, and other resources. A flock usually includes one dominant adult male, a couple of subdominant males, and two or more females that the dominant male watches carefully over.
Social hierarchies in chickens are segregated by sex and manifest as a pecking order in which individuals of a higher social rank may strike out with their beaks; pecking at lower-ranking individuals to ensure access to food and other resources. However, altercations can also include wing pummeling and claw scraping.
In industrial production settings, the chickens belonging to the same age cohort and sex are often kept together. Within groups of female chicks, the pecking order is established by the 10th week of life. However, fights for dominance in groups of male chicks may continue into adulthood.
In situations where one adult bird challenges another, which most often happens when a new bird is introduced into the flock, fights involving males are more often at risk of injury and death than fights involving females.
Domestication and the economic environment
Over the last 7,400 years, chicken domestication has probably occurred more than once in Southeast Asia and possibly India, and the first domestications may have been for religious reasons or for the rearing of fighting birds. Descendants of those domestications spread in several waves around the world for at least the last 2,000 years.
Chickens were a common part of the livestock complement of farms and ranches across Eurasia and Africa for the majority of that time. However, chicken meat only emerged in the early 20th century, and eggs became staples of mass production.
Modern high-volume poultry farms, with rows of cages stacked indoors for heat, light, and humidity control, began to proliferate in Great Britain around 1920 and in the United States after the Second World War. Females, mature hens, and younger chickens, called pullets are raised for meat and their edible egg. Numerous breeds and varieties have been developed by farmers to satisfy commercial needs.
Meat processing was initially a by-product of the processing of the eggs. Only hens who had not been able to produce enough eggs were killed and sold for meat. However, meat production had outstripped egg production as a specialty industry by the mid-20th century. The chicken meat market has since risen exponentially, with worldwide exports reaching almost 12.5 million metric tons, about 13.8 million tons by the early 21st century.
Mature males have long been used for both competition (i.e., cockfighting, which is now banned in many jurisdictions) and breeding. Many immature males (cockerels) are meat birds (capons) castrated (usually chemically, with hormones that cause atrophy of the testicles).