Chickens

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 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.

Roosters crowing (a loud and sometimes shrill call) is a territorial signal to other roosters. 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.

Courtship

To initiate courting, some roosters may dance in a circle around or near a hen ("a circle dance"), often lowering his wing which is closest to the hen. 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.

Nesting and laying behaviour

Hens will often try to lay in nests that already contain eggs and have been known to move eggs from neighboring nests into their own. The result of this behaviour is that a flock will use only a few preferred locations, rather than having a different nest for every bird. Hens will often express a preference to lay in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other. There is evidence that individual hens prefer to be either solitary or gregarious nesters. Some farmers use fake eggs made from plastic or stone (or golf balls) to encourage hens to lay in a particular location. Most of the chickens lay egg in the same place even though their no eggs. 

Reared for meat

Chickens farmed for meat are called broiler chickens. Chickens will naturally live for 6 or more years, but broiler chickens typically take less than 6 weeks to reach slaughter size. A free range or organic meat chicken will usually be slaughtered at about 14 weeks of age.

Reared for eggs

Chickens farmed for eggs are called egg-laying hens. In total, the UK alone consumes over 29 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.