29-04-2013· Left-to-right: Harlequin duck penis, African goose penis, Long-tailed duck penis, Mallard penis. Figure adapted from Brennan et. al (2007). And many duck penises are elaborated with various spines, barbs, knobs, ridges, grooves, and other ornaments (yes, ducks belong the barbed penis club along with cats, most primates, and many other mammals and reptiles, too).