Ducky genitals: the female answer

Only 3% of all avian species possess a phallus, or male intromittent organ. Among these happy few, especially ducks are famous for their relatively long corkscrew shaped penises. From personal experience and observation, I know a flaccid, stretched mallard (Anas plathyrhynchos) penis may measure up to 18 cm, and the Argentine lake duck (Oxyura vittata) tops the bill with a 42.5 cm member (pictured here). The length and degree of elaboration of the penis in waterfowl is positively correlated with the frequency of forced extra-pair copulation (FEPCs, better known as rape): the [duck with the] longest penis has a better chance of dealing with competitive sperm and fertilising eggs.

Surprisingly, no attention was given to the female side of this matter till a team of researchers lead by Patricia L. R. Brennan of the Yale Peabody Museum of Natural History recently took an in depth look into female genital morphology of waterfowl. They found two novelties duck anatomists had never noticed before:

(i) dead end sacs, and (ii) clockwise coils. These vaginal structures appear to function to exclude the intromission of the counter-clockwise spiralling male phallus without female cooperation [?] demonstrating that female morphological complexity has co-evolved with male phallus length. [?] The female morphology we discovered strongly suggests that vaginal genital novelties function as a barrier to phallus penetration, and FEPCs [rape] might be responsible for their evolution.

Now Dr. Brennan plans to build a transparent model of a female duck to see exactly what a duck phallus does during mating. Personally, I would suggest the use of a dead duck.