The Chicken is one of the many mysteries of the night of the Bachelor Party. It is seen roaming about the villa during the awakening and when the three return to look for Mr. Chow's purse.
During the commentary it is revealed that Phil, Stu, Doug and Alan had brought the chicken back from a party (why the chicken was at this party has not been determined) to the villa to feed to The Tiger, although they obviously never got around to doing so.
During the credits' pictures the chicken is shown in random shots at a party.