My chickens are all heritage breeds and forage wonderfully, so with their roo, if they ever decided screw the humans, I wouldn't doubt they'd go feral and start a population easily. Ducks tho, that's just. What. I've seen people try to do the same with rabbits. They just let them go into the woods and three weeks later bunny is food or road kill or frozen bun-cicle because they haven't got any survival instincts.

(Aaaah I want goats, I'd love a little herd of nubians with a boer stud. Raise the babies for meat, keep the good milkers that get big and try for a nicely balance meat/dairy cross).