What is the red thing on top of a rooster's head?

The red fleshy growth on a rooster's head is called a comb, or a cockscomb. There are many spelling variations such as coxcomb. A rooster's comb varies in color, depending on breed and health. A healthy comb is used to attract mates. Large bright red combs are attractive to females.

Small or dull combs are less attractive to hens. The comb helps the rooster stay cool in warm weather with increased blood flow. There are nine possible comb shapes for a rooster, such as the carnation comb, or the walnut comb. Hens also have combs, but they are much smaller.