The Iowa Chicken was a person in a chicken suit who followed John McCain and Rudy Giuliani around Iowa during the 2008 American presidential race, carrying a sign that read "You 'Bawk'ed at the Straw Poll!" This was done to both protest and bring attention to the fact that neither candidate competed in the Iowa Straw Poll. In the past, all Republican candidates have competed in the Straw Poll, and McCain and Giuliani's decisions not to attend represented a break from tradition.
The identity of the Iowa Chicken has not been revealed, but he or she follows an American campaign tradition, including such precedents as 2000's Corn Man.
References
Iowa Chicken Wikipedia(Text) CC BY-SA