Duck humps dog, and other stories from the world of waterfowl sex


I was sure I'd written about the wonderful subject of duck sex on Tet Zoo before. However, having searched the archives I can't find much, which seems odd. Male ducks have large - often very, very large - penises. The text-book example is the Argentine lake duck Oxyura vittata, originally reported to have a 20-cm-long penis (McCracken 2000) (this in a bird about 40 cm long in total), but later shown to sometimes have a penis that hangs for a length of 32.5 cm but stretches to 42.5 cm when fully unwound (McCracken et al. 2001). The Argentine lake duck is a stifftail, a group of ducks that have been described as 'promiscuous and boisterous in their sexual activity'. Perhaps the evolution of the incredible penis has been encouraged by sperm competition; the distal part of the penis in these ducks is brush-like, so it might be that they actually work to remove the sperm of other males before ejaculating their own (McCracken et al. 2001). Proportionally large penises are also present in dabbling ducks and diving ducks.

If male anatomy is remarkable, it follows that the female parts must be pretty interesting too, but because vaginas are more difficult to observe than penises (insert hilarious quip), good data on genital anatomy in female waterfowl has only become available relatively recently (Brennan et al. 2007). This work - widely reported in the popular media - showed that female genitalia in waterfowl are complex, often featuring blind alleys and complex coils. You might predict that male and female parts have co-evolved: the problem is that the vaginal coils often twist in the opposite direction to the natural coil of the penis. This led Brennan et al. (2007) to propose that the evolution of the complicated vaginal structures indicated 'antagonistic rather than mutualistic co-evolution' (p. 4), and that they were there to help prevent forced extra-pair copulations.


And, as you'll know if you've spent any time watching ducks, 'forced extra-pair copulations' are very common in ducks. The Mallard Anas platyrhynchos is the best (or should that be worst?) example of the lot: females are handled so roughly by males (sometimes by groups of as many as 12 males) that it's quite common for people to speak of witnessing 'duck rape', and forced copulation is a common strategy used by males of this species (Young 2005). It's so common that there's even a handbook telling you what to do to discourage it (The Idol Bat Guide to Stopping Duck Rape). Sometimes, female mallards are drowned [adjacent picture from Moeliker (2001); read on].

Indeed, the mallard is so, err, sexually enthusiastic that it will shag virtually anything given the chance, live or dead. I'm sure you're familiar with Moeliker's (2001) famous, award-winning paper 'The first case of homosexual necrophilia in the mallard Anas platyrhynchos'. I was well aware of that. Even I, however, was not prepared for this...

Thanks, I think, to Jason Brunet.

For other articles on sex and sexual organs see...

Refs - -

Brennan, P. L. R., Prum, R. O., McCracken, K. G., Sorenson, M. D., Wilson, R. E. & Birkhead, T. R. 2007. Coevolution of male and female genital morphology in waterfowl. PLoS ONE 2(5): e418. doi:10.1371/journal.pone.0000418

McCracken, K. G. 2000. The 20-cm spiny penis of the Argentine lake duck (Oxyura vittata). The Auk 820-825.

- ., Wilson, R. E., McCracken, P. J. & Johnson, K. P. 2001. Are ducks impressed by drakes' display? Nature 413, 128.

Moeliker, C. W. 2001. The first case of homosexual necrophilia in the mallard Anas platyrhynchos (Aves: Anatidae). Deinsea 8, 243-247.

Young, G. 2005. Northern mallard Anas platyrhynchos. In Kear, J. & Hulme, M. (eds) Bird Families of the World: Ducks, Geese and Swans. Vol. II. Oxford University Press, pp. 513-517.

More like this

What`s next a course in comparative sexual organs in the Animal Kingdom? A paragraph on the Horny Rhino and the Sexual proclivity of the Male Guppy.Perhaps a chapter on the mating activites of the Blue Whale or the Humping of Two Humpbacks and a side show involving the Sperm Whale.
Might make for a best seller titled "Porn in the Animal World".

By Bob Michaels (not verified) on 21 Jul 2009 #permalink

I'm a little pissed at Moeliker. After his paper came out, I sent him a detailed report of a very similar event that we had witnessed, but involving much more detail and several points of interest. He summarily ignored it.

I dunno, maybe I'm just jealous because he got his "first" observation into print, because that kinda ruins it for the second observation...

Those interested in bird sex in general (insert frat boy humor here) may enjoy Jameson, B.G.M. (ed). 2007. Reproductive biology and phylogeny of birds. Science Publishers, Inc., Enfield, NH. There's no foldout, but it does include a classic stifftail-penis photo, and others. There's also a useful review of bird phylogeny, to the extent it was known from published sources in late 2006, by one of my favorite authors.

By John Harshman (not verified) on 21 Jul 2009 #permalink

Arg! So much for my previous comment...

But, seriously, how often have penises re-evolved in birds? Or are they a pleisomorphic thing? Paleognaths don't have them, do they?

By Sebastian Marquez (not verified) on 21 Jul 2009 #permalink

Zach: Don't you mean *ucked up?

Greg: What would Moeliker have done with your report in a more satisfactory of all possible worlds?

By Nathan Myers (not verified) on 21 Jul 2009 #permalink

Thank you for yet another warning about the pernicious threat of duck rape. Maybe this will stop those enablers with their bread crumbs and cracked corn.

By Big Bad Bald Bastard (not verified) on 21 Jul 2009 #permalink

Sorry for the double post...

This clip also represents a role-reversal, with the retriever as victim and the duck as oppressor. While I decry all instances of rape (although the lack of consent on the part of the dog is not proven), it would seem that some form of poetic justice (or at least ironic vengeance)is at work here.

By Big Bad Bald Bastard (not verified) on 21 Jul 2009 #permalink


Paleognaths do have penises, and so do galliforms, so your second guess was right: penises seem to be plesiomorphic in Neornithes. And they seem to be homologous in structure to those of other living archosaurs (including turtles). There are non-homologous structures that might be called penises in three neoavian genera: Coracopsis (a genus of parrot), Bubalornis (a genus of weavers), and Malurus (fairy wrens), and these have clearly evolved independently. There may be more such independent developments, as bird penis research hasn't been all that well funded for some reason.

In most galliforms, the penis has lost its intromittent function (insert more frat boy humor here), but the homologous structure is still there.

All this comes from Montgomerie, R., and J. Briskie. 2007. Anatomy and evolution of copulatory structures. Pages 115-148 in the book I mentioned before.

By John Harshman (not verified) on 21 Jul 2009 #permalink

I wonder if this particular behavior of stifftail duck was ever filmed?

Allegedly, mating of Oxyura ducks often happens during a chase at a distance, so extra long penis can be useful. But I also heard that stifftail males wave their penises during display, so it may be runaway evolution of display structure, similar to the elongated tail of bird-of-paradise...

BBC seems to be more interested in hummingbirds pollinating flowers...

Quack means quack.

I've actually witnessed duck rape. I work at a zoo and a few weeks ago I saw one of our male Yellow-Billed Ducks gang up with a few of his friends, pin down a Fulvous Whistling Duck, and then proceed to rape said Fulvous Whistling Duck.

By Bret Newton (not verified) on 22 Jul 2009 #permalink

For mammal fans, that's roughly equivalent to a human raping a sheep. (Which does happen, of course, but it's hard to put it down to mere confusion.)

By John Harshman (not verified) on 22 Jul 2009 #permalink

Back when I was an undergrad, I gathered that the (basal) avian penis is homologous not only to those of crocs and turtles, but mammals too. So, what does anyone know about the avian clitoris? Or hasn't it been discovered yet?

Songbird sex lasts microseconds, there is no intromission (no time for popcorn and choc-tops... oh sorry, that would be intERmission), but fertilisation does occur at least occasionally. JH's mention of Malurus (I didn't know they were endowed) reminds me of the (anthropomorphism alert!) slutty behaviour of M. cyaneus females and males (no rape here, move along; there's even a special word for malurine promiscuity, 'furgling'), and the question of what reward there can be, in a few microseconds, to make copulation preferable to - oh, I dunno, foraging? They've both got to be rigged with a hair trigger that somehow still needs gental-genital contact. How does that work? But given that it DOES work for them, that could be a sufficient condition for evolutionary reduction and loss of the intromittent bits.

By John Scanlon, FCD (not verified) on 22 Jul 2009 #permalink

At the top of the page when my comment appeared was an ad for

The FUN dating site

I kid you not.

By John Scanlon, FCD (not verified) on 22 Jul 2009 #permalink

But... but where does it keep it? (When it's not using it of course...)

OK, thinking about it, i'm not sure i've ever seen a male (or indeed a female) Oxyura being mobile out of the water - but i'm guessing they don't just swim around with that dangling around ready to be bitten off by any passing fish, so it must be somehow retractable. OK, so whales have a reasonable system, but that's a hell of a lot to retract (i'm assuming it must be flaccid in the dead specimen pictured...)

I've seen mallards gang-raping, to the extent of up to 10 males simultaneously on top of the same female, but oddly didn't see any when i was at Slimbridge Wildfowl & Wetlands Trust the other weekend. Not the time of year for it? (BTW, i don't know how they keep their various rare Anas species from having half-mallard offspring there, as the non-native ducks are all kept wing-clipped, but native species can roam freely around the whole site...)

Another thing about ducks - i've noticed that duck sex ratios - at least from those i see - seem to be skewed heavily towards males - among mallards on urban ponds/canals there seem to be an average of 2 or 3 males to each female, but i've seen groups of Aythya ducks (Tufted Ducks A. fuligula and Pochards A. ferina) with semingly anything from 5-10 males per female. Is this real or only apparent due to behavioural differences?

I have lots of photos of ducks and other anatids from my Slimbridge trip here - feel free to use them (or anything from any of my other galleries) in any of your posts...

Lots of interesting stuff, thanks for comments. Would love to know what was involved in Greg's additional case (see comment 2). Doesn't seem fair to be angry with Moeliker: after all, he was only reporting a case witnessed first-hand.

Are penises homologous across amniotes (see comment 18)? Evidently not: please see the discussion in the article on turtle genitals. Female birds - at least, in those groups where a penis is present in males - do possess a clitoris, though I can't recall reading anything about its homology (though it certainly looks like a small penis in galliforms) or function. Female crocodilians also have a clitoris.

Where do male waterfowl keep their enormous genitals (comment 20)? The organ coils up when not in rest, and is kept folded away right at the back of the cloaca, near the tail base. Even in the most well-endowed ducks, the organ is not so big when folded away, forming at best a gentle swelling beneath the tail. Remember that the organ is erected by being everted and expanded via a lymphatic system, and isn't anywhere near as bulky as are large mammalian penises. Also worth noting is that the penis in waterfowl undergoes seasonal changes in size: I recall the increase being something like six-fold in mallards, but can't find where I read this.

As for sex ratios, waterfowl in general do exhibit male-based skews, especially on wintering grounds. Sometimes males make up something like 70% of wintering populations. This might be because males are larger and more tolerant of cold conditions (and hence that females migrate further afield), but it's also been suggested that females go elsewhere to avoid male aggression. It seems that being a female duck is not much fun.

Terrifying discovery: our corgi, while on a walk one day, just decided to sit down and let his wang hang. No particular reason--he must've just been showing off.

Looks a lot like a big red amphisbaenian, actually.

"Terrifying discovery: our corgi, while on a walk one day, just decided to sit down and let his wang hang. No particular reason--he must've just been showing off.

Looks a lot like a big red amphisbaenian, actually."

Well Zach, I'm going to bed right now, and I'd like to thank you in advance for giving me nightmares.


By Michael Ogden … (not verified) on 23 Jul 2009 #permalink

"Duck rape" is quite a sight to see. I've heard orangutans engage in a similar mating practice -- now that must be disturbing.

By Kevin Schreck (not verified) on 24 Jul 2009 #permalink

Are penises homologous across amniotes (see comment 18)? Evidently not: please see the discussion in the article on turtle genitals.

What about those of crocodiles and birds?

By David MarjanoviÄ (not verified) on 25 Jul 2009 #permalink

Orangutans (comment 25) have raped humans on occasion.

Are crocodilian and bird penises homologous (comment 26)? I've read conflicting information on this. The organs certain look similar (those of crocs and ratites definitely do), but they differ in that the organs of birds are erected by the lymph system (as opposed to erection via blood), and in that the avian organ is asymmetrical (being directed to the left when erected). I think they are mostly regarded as homologous, however. The crocodilian penis is also very similar to the turtle penis in gross structure and location.

What about those of crocodiles and birds?

Again, see Montgomerie, R., and J. Briskie. 2007. Anatomy and evolution of copulatory structures. Pages 115-148 in Reproductive biology and phylogeny of birds (B. G. M. Jamieson, ed.) Science Publishers, Inc., Enfield, NH.

(Apparently yes.)

By John Harshman (not verified) on 25 Jul 2009 #permalink

the avian organ is asymmetrical (being directed to the left when erected)

And that's different from... crocodiles, is it?

By John Scanlon FCD (not verified) on 26 Jul 2009 #permalink

Re: orangutan rape. It would be less hurting than it seems. Apes are much less endowed than humans. Don't know about orangutans, but silverback gorilla in full attention is only 3 cm (yes!) long.

Which explains this permanently frustrated look of a male gorilla.

Apes are much less endowed than humans.


By David MarjanoviÄ (not verified) on 27 Jul 2009 #permalink

The literature is pretty good at providing 'average' lengths for great ape penises. Orangutans apparently have a whopping 3.5 cm as average, both bonobos and chimps are comparatively large at 7.5 cm. Gorillas of both species are about 3 cm. Humans are comparatively enormous, but the primatological literature still says that average penis length across our species is 12 cm: that's 4.8 inches. Magazines on men's health (and other sources) create a different impression.

From what I've watched as a child, Reptile penises are disturbing and monotreme penises are perhaps the most lovecraftian.

I have not seen a crocodile penis, but by assymetrical I assume Darren means that the hemipenes is big on one side and tiny on the other.

On another topic, a cat penis is so disturbingly like a tapeworm's head, that it's no wonder I've had nightmares about "Dune" for so long.

By Tim Morris (not verified) on 02 Aug 2009 #permalink