The environmental characteristics of chickens include living in open pastures and forests throughout Southern Asia, while domestic chickens often live in pens with grass, wood chips or straw. Chickens are herbivores and also eat insects, so plant availability and insect activity are necessary components of a chicken's environment.
Chickens are also very social animals and need to live with other chickens. This is why chickens are kept in pens in captivity, because they are more likely to be sick and unhealthy when kept away from companion chickens. The chicken is also said to be a descendant of the Tyrannosaurus Rex.