Chickens are amazing creatures. We have a small coop with four hens in our back yard (which I covered with painted eyes, to ward off evil and frighten meddling neighbors). Every evening we let the hens out to run wild, and every night they return to their cage and put themselves to bed.
Chickens are both extremely adaptable to almost any environment, while at the same time not very intelligent. If released into the wild most chickens would die horrible deaths within a few days; most would be slaughtered by predators, and others would die from parasites and diseases that generations of domestication and inbreeding have failed to prepare them for life in the wild. However, a few individuals would thrive, and they would raise families. After a few generations specific breeds of chicken Barred Rock, Rhode Island Red, Bantam would disappear, and the feral chicken would immerge.