PENIS IN VARIOUS ANIMALS

Penis of a cock.

Birds

Most male birds (e.g., roosters and turkeys) have a cloaca (also present on the female), but not a penis. Among bird species with a penis are tinamous and ratites, ducks, geese and swans and a very few other species (including flamingoes and chickens). A bird’s penis is different in structure from mammal penis, being an erectile expansion of the cloacal wall and being erected by lymph, not blood. It is usually partially feathered and in some species features spines and brush-like filaments, and in flaccid state curls up inside the cloaca. The Argentine Blue-bill has the largest penis in relation to body size of all birds, while usually about half the body size (20 cm), a specimen with a penis 42.5 cm long is documented.

While most male birds have no external genitalia, male waterfowl have a phallus. Most birds mate with the males balancing on top of the females and touching cloaca, this makes forceful insemination very difficult. The phallus that male waterfowl have evolved everts out of their bodies (in a clockwise coil) and aids in inseminating females without their cooperation. The male waterfowl evolution of a phallus to forcefully copulate with females has led to counter adaptations in females in the form of vaginal structures called dead end sacs and clockwise coils. These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would delay forceful copulation. Studies have shown that the longer a male’s phallus is, the more elaborate the vaginal structures were.

The Lake Duck is notable for possessing, in relation to body length, the longest penis of all birds; the penis, which is typically coiled up in flaccid state, can reach about the same length as the animal himself when fully erect, but more commonly is about half the bird's length. It is theorized that the remarkable size of their spiny penises with bristled tips may have evolved in response to competitive pressure in these highly promiscuous birds, removing sperm from previous matings in the manner of a bottle brush.

Male and female emus are similar in appearance, although the male's penis can become visible when it defecates.

The male tinamous has a corkscrew shaped penis, similar to those of the ratites and to the hemipenes of some reptiles. Females have a small phallic organ in the cloaca which becomes larger during the breeding season.

Rooster

Richard Odei-Nkansah