Spoiler alert! By reading this article, you may come across spoilers from the Chicken Run movie!
The Chickens are from Chicken Run.
They are Ginger's (the main protagonist of the film) friends and fellow chickens stuck in the Tweedy's Chicken farm. They are not as eager at escaping as Ginger, but they do follow her lead whenever she comes up with an idea.
Near the end of Chicken Run, the entire flock of chickens bands together to build a aircraft and collectively use their combined strength to fly out of the farm. They later move out to a island far away from the chicken farm were their able to thrive as a small settlement, and start a new generation of chickens in the wild.