Humans keep chickens primarily as a source of food, consuming both their meat and their eggs. Humans first domesticated chickens of Indian origin for the purpose of cockfighting.
Adult male chickens over the age of 12 months are known as cocks, males less than 1 year old are cockerels. Females over a year old are known as hens and younger females as pullets. The young are called chicks and the meat is called chicken.
Chickens are omnivores. In the wild, they often scratch at the soil to search for seeds, insects and even larger animals such as lizards or young mice. Chickens may live for five to ten years, depending on the breed. The world’s oldest chicken, a hen, died of heart failure at the age of 16 according to the Guinness Book of World Records. Cocks 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 the cock 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 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.
Domestic chickens are not capable of long distance flight, although lighter birds 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.
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. When a cock 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. Cocks crowing is a territorial signal to other cocks. However, crowing may also result from sudden disturbances within their surroundings. Hens cluck loudly after laying an egg, and also to call their chicks. Chickens also give a low “warning call” when they think they see a predator approaching.