How do you tell a male American bullfrog from a female?

Adult male bullfrogs are large, muscular and vocal. They are easily distinguished from females by the very large tympanic membranes that cover their ears. These are much bigger in diameter than their eyes. In females, the tympanic membrane is about the same diameter as the eyes. The chins of males are darkly pigmented, with a distinctive yellow mottle. The chins of adult female frogs tend to be more uniformly white.

The loud basso profundo mating call of the male can be heard throughout the active season - from about April to October. As Mark Catesby - a noted English naturalist in whose honor the species is scientifically named - observed, “…the noise they make has caused their name, for at a few yards distance their bellowing sounds very much like that of a bull a quarter of a mile off.”