Expert: Jonathan Wright - 1/11/2005

Question
Hi Jonathan - bet you didn't expect a question from me.  I remember reading somewhere that ostriches are the only birds that have a penis.  However after some debate on another website, it would appear that lots (most?) birds do.  By this I mean the male of the species of course!  Is this right and if so, why weren't we told this as zoo volunteers?

Answer
Dear Mary

Thanks for your question. It makes a change to get a question from someone I know. Gary sent me a question about a year ago, "Why are aye-ayes so ugly?" but I think that was a wind-up.

I have looked up various books and websites to find the information for you. Most of the sites seem obsessed with the Argentine lake duck (be patient), although one site wonders why the relevant websites get many 'hits' a week. Several sites state that swans are the only birds with penises, but this is contradicted by my research, although there are several birds with 'phalloid organs' which may, or may not, technically be penises.

http://www.exn.ca/Stories/1997/02/19/06.asp and http://birding.about.com/library/weekly/aa071700c.htm mention about bird mating. The males of only 3% of bird species have a penis, perhaps because females prefer it that way, as they have control over males without a penis and can control which sperm reaches their eggs. Most birds copulate by briefly touching genital openings in a ‘cloacal kiss'. One scientist suggests that the penis evolved because males needed it to advertise its sexual prowess and to force copulation.

Bigger birds, including ducks, geese, swans, ostriches, cassowaries and kiwis continue to have a penis. This penis is generally spiral in form so that it can reach the female sex opening, which lies to the left in the cloaca. The rhea has an extrudable organ. As waterfowl sometimes copulate in water, the penis helps ensure that the water does not wash away the sperm. The Australian blue duck, for example, has a penis so large that when it finishes copulating the bird has to turn on its back and stuff its penis back into its cloaca.

http://www.abc.net.au/science/news/enviro/EnviroRepublish_366856.htm mentions the Argentine lake duck (Oxyura vittata), which has a 42.5 cm long penis, as long as its body - nearly half a metre long. This is the longest bird penis to date and may be an example of 'runaway' sexual selection, where female preference drives male anatomy to ever-greater extremes. This species is promiscuous and boisterous in its sexual activity, with drakes competing to mate with the ducks. The drake may use the brush-like tip of its penis to scrub the sperm of previous mates from the female's oviduct.

http://www.wholeearthmag.com/ArticleBin/338.html discusses cassowaries. The male cassowary has an organ that looks remarkably like a penis. This phallus does not discharge semen internally. It is "invaginated," having a tube-like roll of tissue that opens at the tip of the "penis", but is not connected internally to the male reproductive organs. The male's vagina-like cavity is used to retract the phallus by turning it "inside out" (so the non-erect "penis" resembles the finger of a glove pushed inward). While the male inserts his erect phallus into the female during mating, he ejaculates semen through his cloaca, an orifice at the base of the phallus that also doubles as the bird's anus and urinary organ.

Female cassowaries mate, lay eggs, defecate, and urinate all through the same orifice, the cloaca, which is exceptionally large in this species, being capable of passing eggs weighing up to 1-1/2 pounds. All female cassowaries also have a phallus, which is essentially identical to the male's phallus in structure but smaller. The "female phallus" is sometimes referred to as a clitoris, but it would be equally valid to speak of a "male clitoris," since the male cassowary's "penis" is not an ejaculatory organ. The cassowary's genital anatomy exhibits a juxtaposition of "masculine" and "feminine" traits: both sexes possess a penis/clitoris and also have another genital orifice that doubles as an anus.

Many New Guinean people consider cassowaries to be androgynous or gender-mixing birds, or to be all-female species or to be simultaneously male and female. The Sambia consider all cassowaries to be "masculinized females," that is, biologically female birds that nevertheless lack a vagina and possess masculine attributes (they're thought to reproduce or "give birth" through the anus). Over a dozen cultures elevate the cassowary to a pre-eminent position as a generative figure, a powerful female creator of food and human life. The androgynous cassowary is also considered to be an intermediary of sorts, between the animal and human worlds.

The gender-mixing cassowary reaches its greatest elaboration among the Bimin-Kuskusmin people. In this remote tribe of the central New Guinea highlands, the cassowary presides over an entire pantheon of androgynous and sex-transforming animals. At the pinnacle stands the creator Afek, the masculinized female cassowary, and her brother/son/consort Yomnok, a feminized male fruit bat or echidna (a spiny anteater, an egg-laying mammal related to the platypus). Both are believed to be hermaphrodites possessing breasts and a combined penis-clitoris. Afek gives birth through two vaginas (one in each buttock), while Yomnok gives birth through his/her penis-clitoris.

Nature (Vol 399, 6 May 1999) states that male buffalo weavers (Bubalornis) have a false penis or phalloid organ and show intense sperm competition, where unrelated male coalitions defend multiple nest chambers. The organ is a stiff rod of connective tissue, lying anterior to the cloaca. It lacks ducts and is not homologous to the penis in other bird species. Females have a much smaller phalloid organ. The male's organ seems to be a stimulatory organ. After protracted copulation, the organ generates an orgasm-like state in males, unlike other birds.

I hope this has helped your research. I can only suggest that zoo volunteers are trained to provide information which can be told to children, or perhaps the trainers are embarrassed by the subject. My A-Level Zoology teacher did not teach us about reproduction in rabbits or humans - we had to read it from a book. She also didn't teach about evolution. I think she was a victim of a strict religious upbringing, but I cannot state whether this applies to zoo volunteer trainers.

All the best

Jonathan