You can sculpt a chicken or anything else for that matter from styrofoam, sold as flat boards in home improvement stores. Cut a couple or three pieces to the rough size of the chicken and glue them together using spray adhesive. Now you have a thick block of styrofoam. Using a serrated knife, (steak knife works fine) carve the shape of the chicken. The piece doesn't have to fool anyone from up close, but from a distance it should look OK. With a rough piece of sandpaper, sand the shape smooth, and have your set artist paint it with acrylics to look like a roasted chicken. If you have to use spray paint, first brush on a coat of Elmer's glue. Spray paint has the tendency to dissolve the styrofoam, and Elmer's glue will seal the foam and protect it against the solvent in the spray paint. Spray after the glue has dried.

It would be a good idea to bury something heavy in the center of the chicken to give it some weight. If the chicken breaks, you can put it together again with spray adhesive.