The Sentry Chickens were created by Roberto, an engineer who was searching a new method of helping a survivor during a fight. Since the Sentry Chicken is essentialy a mobile and more poweful version of the Sentry Gun, it can be stated that the project was sucessful.
Sentry Chicken is a live, walking turret helpful for extra firepower in battle. It stays within close proximity of the player and the turret on its back automatically targets Zombies and shoots at them in short bursts. When zombies get too close, the chicken will run away from them. It stays on the battlefield until the turret on its back runs out of ammo, then it destroys itself, therefore killing the chicken.