Duck sex: to interfere, or to watch?

Ducks - like the Mallards Anas platyrhynchos shown here - lead fairly violent sex lives. As I said in a previous article...

[A]s 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) 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.


Over the weekend I was fortunate enough to be close witness to a vigorous bout of duck sex. There's an unavoidable feeling of pity for the harassed, roughly handled female, and I can understand the urge to interfere. But, in the end, what good does this do? If you interfere, it's not as if the males give up and go and do something else.





Maybe those nice people who endorse the Abolitionist Project have plans to re-programme ducks so that they become more gentle lovers, or learn to rely on porn for their kicks or something.

For previous thoughts on waterfowl sex see...

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Speaking as a farmer who regularly witnesses all sorts of unappealing poultry sex, I wish all sorts of good luck to those with so much free time on their hands that they can intervene is poultry sex.

This reminds me of an old joke.

"What is the difference between kinky and perverted?"

"Kinky is when you use a feather during sex, perverted is when you use the whole chicken."

I wonder if this is an adaptive response by low-status males who would never get any otherwise, but can achieve at least some chance of reproduction by banding together. It might be the light, but the male on the left in the first two shots seems to have a very dull bill, and it's the bright yellow that attracts the ladies. He is, in other words, a total loser. Perhaps his friends are too.

By John Harshman (not verified) on 23 Mar 2010 #permalink

It's not the light: one of the drakes really did have an unusual grey bill. Your hypothesis is a fine one... but, don't _all_ mallard drakes engage in this sort of ganging-up behaviour?

I don't know of any research on correlations between mating success, or studliness, and forced copulation. A male who has a mate already is likely to be busy defending her from other males, and so by default have little time for forced copulation. Of course that's a major tradeoff for many species: mate-guarding/parental behavior vs. extra-pair copulation and courting. And it doesn't have to be all or nothing; different males may budget their efforts differently without any putting all their effort into one behavior.

By John Harshman (not verified) on 23 Mar 2010 #permalink

Heh, this reminds me of the classic paper on the necrophiliac-homosexual-mallard-incident:

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

[from Darren: click on the link at the bottom of the article above!!]

...and I quote, from the abstract: "On 5 June 1995 an adult male mallard (Anas platyrhynchos) collided with the glass façade of the Natuurmuseum Rotterdam and died. An other drake mallard raped the corpse almost continuously for 75 minutes. Then the author disturbed the scene and secured the dead duck. Dissection showed that the rape-victim indeed was of the male sex. It is concluded that the mallards were engaged in an âAttempted Rape Flightâ that resulted in the first described case of homosexual necrophilia in the mallard."

I was just having a conversation about "duck rape" and waterfowl genitalia the other day. What good timing for a post on the subject! Thanks Dr Naish!

Is the violent sex life of mallards one of the reasons that mallards are the most common duck in the world?

By Dawn Gilkison (not verified) on 23 Mar 2010 #permalink

Somebody could check what really is social system of mallards.

I observed males guarding their feeding territory, that is chasing any other ducks away from a patch of weeds on a pond where 'their' female and chick fed. Because chick mortality is huge in mallards, probably there is a trade off between promiscuity and guarding brood.

Why only some behaviors of living animals are picked by paleontologists, and not the most interesting ones?

Imagine a group of male tyrannosaurs trying to rape a female. Or even better, sauropods. With so big broods, female unable to hide, and few mating opportunities, every male sauropod in mass rape could realistically hope to fertilize at least a few eggs.

Compare group courtship of humpback whales and sea turtles. :->

Jerzy, that would be odd, since the common wisdom is that male mallards desert the female during incubation and have no further interaction with her. Considering how well studied mallards are, it would be prudent to question the meaning of your observation.

By John Harshman (not verified) on 23 Mar 2010 #permalink

seabold @ 2 : The version I know is as follows.

Erotic is using a feather.
Kinky is using the whole chicken.
Perverted is inviting the local vicar for chicken dinner the following day.

Assuming that Anseriformes are similar in this, and that it's not just a duck thing, is it any wonder that when the Greeks described Zeus taking on the form of a bird to impregnate Leda they chose a swan?

By Allen Hazen (not verified) on 23 Mar 2010 #permalink

Actually, anseriforms vary quite widely. You may remember that swans mate for life. (Poor analogy to Zeus.) I imagine that forced copulation is unknown in swans. The reason Zeus picked a swan is probably just that they're big birds and are among the few with penises. Anyway, I seem to recall that Leda was willing.

By John Harshman (not verified) on 23 Mar 2010 #permalink


I imagine that forced copulation is unknown in swans.

That seems to be the case. Interestingly, forced copulation has been recorded in two species of true geese: the snow goose and Ross's goose. It has also been observed in some species of whistling ducks, perching ducks, pochards, sea ducks, and stiff-tails, but for the most part, forced copulation is a dabbling duck thang (see Table 2 in McKinney et al. 1983).


McKinney, F., Derrickson, S.R. & Mineau, P. 1983. Forced copulation in waterfowl. Behaviour 86, 250-294.

@John Harshman

that would be odd, since the common wisdom is that male mallards desert the female during incubation and have no further interaction with her. Considering how well studied mallards are, it would be prudent to question the meaning of your observation.

I have observed the same, and even cases where the male seemed to take over caring (if that's the right word) for his offspring after the female was run over. Other things I have observed is lost/abandoned chickens from different broods and ages teaming up to form large groups that stick together. I've never read about that in the literature either.

By Kilian Hekhuis (not verified) on 24 Mar 2010 #permalink

"Forced copulations" are hardly unique to mallards.

As I do recall, I remember reading that male orangutans (of both species, I think) go through a period where the only copulations are forced copulations. It is only when they get the disks on the sides of their heads and are fully mature that females seek them out.

Mallards (and many other ducks) do seem to have a habit of brood amalgamation, or creching. Since female ducks don't feed their young, an extra member of the group is no trouble, and may improve survival chances for all the ducklings, since a predator is less likely to choose any particular member of the brood. Dunno about chickens, but it's all over the duck literature.

What isn't in the literature, as far as I know, is male parental care in mallards. It would be interesting to document this behavior.

By John Harshman (not verified) on 24 Mar 2010 #permalink

Unfortunately, I didn't document it. Just saw it on the city pond.

This is mostly what I saw and never backed up from wisdom from ornithology. However, it was strikingly like behavior of geese, where males defend the feeding area (which can change) from other broods. Politics within mixed colony of geese was very interesting.

BTW, in waterfowl in many species and situations it is very false that extra chick in the brood is no trouble. Broods are limited by food avialable, and there is visible competition for food between broods and within broods. Chick mortality from undernourishment is big, eg. mallards in cities often raise on average like 1,7 chick per brood.

Adopting chicks younger than own brood may be little cost for female (because they will lose competition for food to her chicks) but not equal or bigger chicks. Compare situation in coots, where competition within brood is well documented.

Which makes interesting speculations how clutches of herbivorous dinosaurs behaved. :)

Coots feed their chicks, which is why they raise so few and why there's competition. Now it may be that mallard ducklings in large broods compete with each other in very high-density populations, but I would like to see that documented too. Generally, the literature on brood amalgamation finds no cost to the practice.

By John Harshman (not verified) on 24 Mar 2010 #permalink


Mallards (and many other ducks) do seem to have a habit of brood amalgamation, or creching.

Crèche formation is particularly common in some sea ducks, notably common eiders Somateria mollissima. Among eiders, certain females even seem to be actively trying to take over other broods and add their ducklings to their own. Brood take-overs in eiders are not always or even usually violent, however; to the contrary, females with broods often join together on what appears to be a completely voluntary basis. (There is quite a lot of literature on this subject.)


Broods are limited by food avialable, and there is visible competition for food between broods and within broods. Chick mortality from undernourishment is big

I'd like to see a citation for your claim that malnutrition is a typical cause of juvenile anatid mortality. A number of years ago, I spent a couple of field seasons specifically observing eider crèche dynamics. If there was significant food competition between the ducklings, it certainly wasn't very 'visible', not even in those cases where the crèches consisted of two dozen or more ducklings. There was plenty of duckling mortality all right, but AFAIK the main causes of death were poor weather conditions, disease, parasites, and predation* (though not necessarily in that order).

* Mostly by large gulls but on one memorable occasion I saw how two white-tailed eagles Haliaeetus albicilla repeatedly swooped down on a brood of eiders, with the obvious intention of catching ducklings (though I'm not sure if the eagles were successful; my observation was made at quite a distance).

Oh dear, is it that time of the year again? Taking a walk around the pond in the park now is not as relaxing as it should be...

I must admit I have often wondered why male gang-ups and forced copulations aren't more common, seeing as many species have an overlap of males that will otherwise not be able to reproduce. Is it the fact that it requires some degree of cooperation from the males? (Or how much is required, really?)

May I just say that this, the Talpanas stuff, the penguins, the babirusas... it makes me so glad that you stuck with the blogging, even through the New Year horrors. Hooray!

Neil: when next we meet, I owe you a hug :) And that wasn't inspired by the content of this article.

It's great and everything that homosexual necrophilia has been documented in the primary literature, but I've seen it on several occasions. At MSU, the earth sciences department is right next to the duck pond, so myself and other students have witnessed all sorts of weird (duck) sh*t. Usually it revolves around a duck being hit by a car, and subsequently being gang raped. Gang rape in the water is always hard to watch, because from the gurgling sound emanating from the females head (which is being held underwater) it sounds like she's being drowned (albeit inadvertently).

We witnessed a major WTF on the night my girlfriend and I started dating - we were sitting on a bench at midnight, and a female wandered out into the street, and a passing car sped up, and her head made a very clear "DING" sound off the bumper, and the animal collapsed. The car drove off, and we sat there in mild horror, until all of a sudden the head sprang up, looked both ways, and then she got up and shook her tail feathers, and started walking back to the pond, where she was promptly gang raped, not even 30 seconds after being hit (by a car going 35 mph) and her resurrection.

I think there is a difference between eiders and mallards, and maybe between populations of mallards, too.

I am now BWP-less, but references to brood reduction of Coots (which have feeding ecology much more similar to mallards) are in the famous paper of counting coots.

No, mallards are not like coots. The relevant feature of feeding ecology here is that coots feed their chicks, while ducks don't. It's parental effort that limits the size of coot broods. Duck broods are limited, if at all, by the female's ability to produce eggs and incubate them. Even brood parasites appear to have no cost in ducks.

By John Harshman (not verified) on 25 Mar 2010 #permalink


I think there is a difference between eiders and mallards, and maybe between populations of mallards, too.

Thanks for your opinion, but if you don't mind I'd rather have a reference to the primary literature. And to reiterate, I was asking about anatids, not coots.

Re Leda and Swan-Zeus: I recall reading (was it in Lorenz?)that male Mute Swans are in the habit of forced copulation with female Swans when females are sitting on their nest (other than their own mates). The female won't leave her eggs, so can't escape. And that male Mute Swans occasionally mistake white-skinned European sun-bathers on lake-sides for female Swans, with predictable results..
Given a populace given to mythic rather than scientific thought,
this would only have to happen once or twice to get enshrined in mythology.

I prefer that people use Pubmed themselves. Try:

Drummond H. Dominance in vertebrate broods and litters. Q Rev Biol. 2006 Mar;81(1):3-32.

Black JM et al. Determinants of Social Rank in Goose Flocks: Acquisition of Social Rank in Young Geese. Behaviour, Volume 102, Numbers 3-4, 1987 , pp. 129-145(17)

references in: Poisbleau et al. Within-brood social status and consequences for winter hierarchies amongst Mallard Anas platyrhynchos ducklings. Journal of Ornithology 2008.

Poisbleau et al. Looking like mother makes mallard ducklings dominant over their siblings. Behavioural Processes
Volume 83, Issue 1, January 2010, Pages 127-129

But interestingly, sibling competition in broods seems understudied.

If you look for malnutrition especially - food resources, predation and sibling/brood competition are interexchangable. Lack of food forces broods or ducklings to compete, and subordinate ones are forced to feed in places vulnerable to predation. If you need clear examples of malnutrition, I suggest looking for studies of urban waterfowl, which typicaly rear very few young.

Jerzy, this is what you wrote in comment #21:

Chick mortality from undernourishment is big

and this is what I wrote in response in comment #24:

I'd like to see a citation for your claim that malnutrition is a typical cause of juvenile anatid mortality.

The main issue here is your allegation that a significant amount of duckling mortality is caused by malnutrition. Thank you for providing sources but they do not really talk about juvenile anatid mortality; they do talk about inter-brood competition, but competition does not automatically lead to death. (Speaking of that competition, one of your references, Poisbleau et al. (2009 [sic]), says that 'because ducks are precocial, feed themselves and thus do not show siblicide, they probably do not compete for food or space as intensively as altricial chicks' [p. 201; emphasis mine].)

sibling competition in broods seems understudied

Then how can you claim so confidently that competition = food competition, and that competition -> malnutrition -> significant mortality?

I prefer that people use Pubmed themselves.

In science, it's the one who makes the claim who has the responsibility to back up the claim if/when requested.


Poisbleau, M., Guillemain, M., Demongin, L., Carslake, D. & David, J. 2009. Within-brood social status and consequences for winter hierarchies amongst mallard Anas platyrhynchos ducklings. Journal of Ornithology 150, 195-204.

FEPC (forced extra pair copulation) is a common strategy in Northern Hemisphere ducks. Particularly dabblers and most obviously Northern Mallard. This is most likely a consequence of migratory behaviour and the habit of nesting in often unpredictable habitats. Paired males will defend their mate until completion of the clutch - they are defending paternity not the female. It is possible that the female has chosen a poor quality nest site and the water will be inadequate for brood rearing. Therefore, the male will try to invest in as many other females as time will allow - all being guarded while receptive and all guarded by males with the same view in mind! It is likely that the male will have to force himself onto other females and get past their mate aggressively. However, females probably know better than to trust their mate's vigour and will undoubtedly look for extra males too. Its not pretty but it is a good strategy for both sexes.

In modern urban environments the availability of food means that Northern Mallards no longer migrate. They are bigger too. The use of FEPC in these environments is always obvious and generally involves a lot more individuals than similar occurrences in truly wild mallards. One facet of sperm competition in this species is that the last male to copulate is probably the one that will be most succesful. Hence the pile-ups and, therefore, at some point the defending male will realise he better join in and make sure he's last. The male Northern Mallard - ever Nature's gentlemen!

Ducks of more stable habitats like the marsh living Shoveler rarely use FEPC. Southern Hemisphere species too, even the nomadic ones. The much loved Meller's Duck would consider FEPC a very distasteful practice and another example of the differences with its northern relatives!

By Glyn Young (not verified) on 29 Mar 2010 #permalink

Our local wild ducks are around the park all year but
every year when the ducklings arrive the males gang up on the females when she has new ducklings. I can understand the 'gang rape' referred to on a female duck but why do the males attack her when she has 8 or 9 ducklings in tow????
We have a lot of 'homosexual ducks' but that is usually one on one where as the males usually attack the females with her brood 5 or 6 at a time.!!!!