Source (+ a few other strange anatomical features of birds, none as interesting as this one)
Most male birds do not have a penis, but some that do seem to make up for the rest. The Argentine lake duck’s penis is shaped like a corkscrew and can extend to 17 inches. Seventeen. Inches. The bird is only about 16 inches tall.
Argentine lake ducks practice forced copulation and the females are often observed trying to get away. Possibly the long penis evolved to make reaching a female easier. Or conversely, the long penis could be the reason the females try to escape.
I bet most of us wish we could be that much of a grower.