|The Question: Why would five mallard drakes gang up on a female mallard with chicks trying to drown her?
Submitted by: S., British Columbia, Canada
Warning: I have to begin this answer by warning against applying human moral standards to animals, because it’s very easy to do in this situation. But mallards aren’t thinking about right and wrong when they engage in behaviors. They’re acting in the ways that have proven reproductively successful. They aren’t being mean or immoral.
The Short Answer: The short answer is that the mallard (Anas platyrhynchos) males (drakes) are forcing the female mallard to mate with them. And for the reasons discussed below, forced copulation is far more common in waterfowl (ducks, geese, swans) than in other types of birds. Mallards are most famous for it, probably because they are the most commonly seen duck and can now be found nearly worldwide.
There is a significant skew in the sex ratio of mallards in favor of males, so in any mallard population there are a number of unmated males. By forcing copulation with a female who is mated to another drake, unmated drakes gain a chance to pass on their genes. And if those genes include genes that favor the forced copulation behavior, it will be likely to persist. But it isn’t just the unmated males who take part in the forced copulations. In fact, males who have their own mate are even more likely to force copulations with females other than their mate.
This is simply the way things work in the world of ducks, but for us humans, it can be hard to watch. The drakes you saw were not trying to drown the hen. Mallards mate on water as well as on land and the drakes may just have caught up to this hen on the water, or she may have tried to escape by going into the water. In the vast majority of cases, the hen will eventually escape. They do sometimes get injured or even killed in the course of forced copulations, and that’s probably because they simply get battered and smothered by all the aggressive males. There are records of as many as 39 drakes chasing and repeatedly trying to copulate with a single mallard hen, although typically, only one or two of the males will actually copulate with the female.
This video is one of the milder ones you can find on youtube: http://www.youtube.com/watch?v=Y1X-7FeddeI
More Information – Why ducks? It’s been shown that in most (if not all) birds, females will accept and even solicit copulations with males other than their mates. Even in birds that have one-to-one pairings that last years and years, females will occasionally copulate with males other than their mate, especially if the male is of higher quality or is higher on the pecking order than the female’s mate. The standard explanation for this is that these females are gaining direct benefits such as access to food or territory, or indirect benefits such as “better genes” for their offspring. Even when females are not actively seeking copulations with other males, females of most species do not vigorously resist copulation by males that are not their mates.
What’s odd about mallard hens and hens of many other waterfowl species is that they resist and resist very vigorously, to the point where they risk injury by aggressive males. Why do they do that?
There are several theories:
- Female mallards already have “good genes” at their disposal. The very fact that there are more males than females means that females get the pick of the male crop when they pair up. Most females are already mated to a high quality male and any unmated males are the ones who have been rejected by other females and are therefore probably of lesser quality. Females don’t want to mate with the lesser males so they resist forced copulations. If this were the driving factor, however, you’d expect to see flexible behavior on the part of females. They should resist forced copulations by low ranking males and welcome matings from high ranking males. But what is observed is resistance to all males.
- The presence of a penis. 97% of bird species do not have a penis. Males simply rub their cloaca (combined urinary, intestinal and reproductive opening) against the cloaca of the female, and release sperm. It appears that it is very difficult to rub cloacas if the female resists. Waterfowl on the other hand, have what anatomists call an “intromittent organ,” or what most people would call a penis. And it appears that mallards can forcefully insert this penis before ejaculating. Of course, this immediately raises the question of which came first, the penis or the forced copulation? Do ducks engage in forced copulation because having a penis makes it possible? Or did the reproductive success of forced copulation favor the evolution of a penis to make it even more effective? There is some evolutionary evidence that the first birds had penises, suggesting that the penis came first. So then the question becomes why do waterfowl have penises and other birds don’t? One answer may be that waterfowl often mate on water, where a penis that introduces sperm into a female’s reproductive tract may help prevent sperm from washing away or being damaged by water. And because ducks have a penis, they may be able to force copulations, where the 97% of birds that don’t have a penis are simply unable to force copulation. And the presence of a penis may contribute to the resistance behavior because it’s been shown that venereal diseases, which can take a heavy toll on female birds, are more common in birds with penises. Presumably, because the penis is forcing bacteria and other disease-causing organisms further into the female’s reproductive tract, the risk is greater than in birds that simply rub cloacas. So maybe the resistance of female ducks is an attempt to limit the number of copulations to avoid disease.
- Maintaining pair bonds. There is some evidence that male ducks who witness a mate undergoing forced copulation are more likely to abandon the female and her nest, presumably because the male can no longer be sure the nest contains his offspring. So maybe female ducks resist forced copulation to keep their mate from abandoning them. But this doesn’t explain why female ducks resist more than other birds, since males in many other bird species provide far more help to their offspring in terms of feeding and protection. This would suggest that females in those species should work even harder to maintain the pair bond. Yet they don’t.
- Are females creating competition? In non-waterfowl birds in which females allow and even seek out extra-pair-copulations, females sometimes seem to encourage competition between males. This may be a way of figuring out which males have the “good genes.” It has been suggested that female ducks may be engaging in an extreme version of this. By forcing males to chase them, sometimes for quite long distances, and making multiple males compete for the chance to force copulation, female mallards may be conducting a very strong screening for “good genes.”
- Choosing males who are successful. In some bird species only a few males get most of the matings. For example, in many species of grouse, the males display in a prominent location and females choose which male to mate with. Often, nearly all the females in one location will pick the same male or one of just a couple of males. Females are presumably choosing on the basis of good genes. But one factor of “good genes” is whether the male is attractive to the other females and whether the male’s offspring will share their father’s attractiveness to other females. This favors both the genes of the attractive males and any females who mate with them. In the case of the mallards, this would mean females may “choose” males who are successful at forced copulations because they are likely to pass that trait on to their sons, resulting in numerous grand-offspring for the female who mates with such a male. And the way females “choose” is by resisting all males, thereby ensuring that only the males who are most effective at forced copulation will be able to fertilize their eggs.
As is often the case with a complex system like this, I suspect the answer is some combination of the above factors and maybe others that haven’t yet been identified. Margo Adler, a researcher at the University of New South Wales, believes that females are making the most of a bad deal. Like female birds in other species, female waterfowl want the best genes for their offspring. But they also want to avoid disease. They would probably avoid forced copulation if they could and only mate with the males they choose to mate with. But because male ducks have penises, they are able to force copulations. Given that the females probably can’t avoid forced copulations entirely, they resist vigorously, so that at least if they have to undergo forced copulation, only some males are successful. The males that are successful are likely to pass on the traits that made them successful, which means that the female duck’s male offspring are likely to carry those traits and also be successful at forcing copulations … and that’s how natural selection works.
Why So Many Male Ducks: One question you might be wondering is, “Why are there more male ducks than females?” It turns out that at the time of hatching, the sex ratio of baby ducks is pretty much even – the same number of males and females. But in adult mallard populations, there may be 10% more males than females. Why is that? It appears that female ducks are particularly susceptible to mortality. It has been shown, for example, that female ducks fall prey to foxes and other predators at a higher rate than males, probably because only females sit on the large, difficult to hide, nests. It’s also possible that simply building all those eggs – mallards may lay a dozen eggs and have two or three clutches each year – puts a nutritional strain on females that reduces their survival. For whatever reason, survival of females is lower than that of males, which results in the excess of males, contributing to the forced copulation behavior.
By the way, forced copulation behavior seems to be most strong in parks, where many ducks are crowded together and where the sex ratio skew seems to be strongest. So if you find it hard to watch this behavior, it may be some consolation to know that it is less common “in nature” than it is in the parks where people often witness it.
Sources: Thank you to Margo Adler, PhD, for her help.
Cunningham, E. (2003). Female mate preferences and subsequent resistance to copulation in the mallard. Behavioral Ecology, 14(3), 326-333.
Adler, M. (2010). Sexual conflict in waterfowl: Why do females resist extrapair copulations?. Behavioral Ecology, 21(1), 182-192.
Donald, P F. (2007). Adult sex ratios in wild bird populations. Ibis, 149(4), 671-692.
Hi Carol, I don’t think mallard drakes are doing what’s best for the species. Natural selection doesn’t work that way. They are doing what’s best for themselves as individuals. I don’t know that it has been studied in mallards, but in many species in the animal world, it has been shown that males sometimes kill the young of females so that the females will mate again. If a mallard female is sitting on a nest with eggs and a male who is not the father of those eggs destroys them, the female might renest, and if the egg destroyer is still around and gets to mate with her, he might be the father of her next brood. Prior to destroying the eggs, he was the father of no one. After destroying the eggs, he might be the father of 10-15 ducklings. That perpetuates whatever genes he has that favor that behavior. You are right that it is possible for that to lead to decline in the population of a species. And it’s not favorable to the poor mallard hen. For her, all the energy she put into the first clutch of eggs is completely wasted. But I don’t think you have to worry about the overall population of mallards. There are probably more mallards now than ever before and they’ve been introduced all over the world. They are a very successful species in terms of numbers. Tom
I have been observing a community of mallards in a local park. They socialise in kinship groups. Usually one female and her mate, accompanied by a male who may in fact be a relative. There has been little conflict, young males will become hormonal and try to approach a mature female. The two males will then fight the young one off. If he climbs on top of a female they will almost kill him. The young ones quickly learn that they must socialise to meet a breeding mate and they behave themselves. Divorce happens but like the swans, it is not common. I have been observing the group for a year, fist concentrating on the swans but the ducks were too communicative to be ignored.
Very interesting. Thanks, Tom
In My Garden, ducks are regular visitors here….They are usually
absent except for a lone male now and then during the summer, and fall, but in the winter, especially this winter, 50 or 60 are coming in to eat the Bunnies corn and the seeds that I put on the ground for small ground feeding birds…
Its February and have not noticed any breeding behavior, perhaps food overtakes the breeding instinct, but I have noticed that the females allow the males to eat first, then the piling of all the males and females on the corn starts with a frenzy…I do have a question…As the ducks are lying on the snow at the food pile, they tuck their feet up almost to their wings in many cases lying on the ground looking like little roly poly canisters…As swimmers in ice water at the pond, it would seem that the cold would not affect their feet, but on the ground in the snow, many look like they are having a hard time with the snow on their feet..
Thank you for writing this article. I saw two Mallard drakes attack a hen at the lake yesterday. She even had ducklings with her. Interesting……
There’s a female that have babies every year at our house boat balcony. The same day her ducklings hatched another male than the father tried to rape her and has continued to try every day. The female screams and fly away but has to come back to protect her ducklings. The father protects her if he’s with her (which he often is). But he scares his ducklings away from him everytime they eat (competing for food or wanting to get them away from the mother?) which is annoying to see. I think the ratio of females and males need to be fixed.
I encountered a situation similar to what is outlined in the article above, at a waterway in my town, where a group of ducks appeared to be ganging up on another duck that was different in appearance, pale shades, and trying to drown it.
At first, I thought it was some sort of playful interaction, but it was the first time I’d seen it go on for this long in this area that I frequent about 2 to 3 times a week and I’ve never seen it carry on like this. The lone duck that was targeted, appeared weaker, and I began to worry. So I intervened, I went over and began splashing water on the ducks that ganged up on the lone duck, then began lightly tossing some pine cones on the ducks with the intent to get them to scatter and stop what appeared to me to be a something that was just wrong. A lady rowed up on her boat, asking what I was doing as if I was trying to cause harm, which I know probably appeared that way from a distance, but I was just thinking about how crappy this experience must be for the lone duck, knowing nothing about ducks or mating habits and such. I simply explained to the woman that these ducks were trying to drown the other duck, and she proclaimed “that’s just nature man”, to which I replied after successfully breaking up their attempts to drown the duck with a few more pine cones to the back of these savage ducks, “Well, I guess you could say I’m nature too.”
JC – very well done! And I love your comment back to the misguided female rower!
After I built a pond, we have had “wild” mallards in our backyard for the past 30 years. We feed them throughout the year and we usually have a nest or two this time of the year. There has always been some ducks that are more aggressive to others but nothing like last night. Seven drakes were “attacking” a hen for a very long time so I tried to intervene and let her get away but she would scamper towards one of the drakes and lay down with her wings spread whereas the drakes would continue their onslaught. Finally the drakes dispersed, but the hen was on her back. She was barely alive when I put her in a box with some water and placed it in the garage. When it was getting dark, and the other ducks were gone, I took her out to the pond and placed her in some plants/bushes. She was sitting up, but still looked weak. This morning when I checked on her, she was dead. Was she aggressively seeking that attention from the drakes or it natural for the drakes to kill off competition of their mates?
Hi William, thanks for writing. That sounds pretty awful to watch. Mallard mating can be that way. I would assume the female was trying to entice her actual mate, but the rest of the gang was taking advantage and overwhelming the pair. Sorry it went so badly. Tom
We have had a pair of crested ducks on our lake for years. They were a mated pair. But now 3 rouge ducks have come and have either chased the male away or killed him. Every time the whited crested gets in the water the rouge ducks speed over and pounce on her and hold her underwater. They want to keep her on shore. We are so afraid they will drown her as they hold her under water so long. Wish we could get rid of the rouge ones.
We have a pond with ducks. For the first time in 20 years, four male ducks ended up in our yard and were attacking a smaller female. We chased the males away, the poor female was breathing but weak. We put her in a box and were going to bring her to a rehab place, but she died shortly after putting her in the box! So disturbing! Now it seems like there’s several really aggressive males chasing all other ducks away and very few females. If I see those males doing that again in my property, my baseball bat is going to send them to another pond!
Just witnessed female mallard duck killing a tiny bluetit which had only just fledged in my garden. She had its neck in her beak. I rushed to try to save bluetit, but it was so severely damaged I had to put it out of its misery.. Earlier I’d photographed bluetit on its nest perch – such a fluffy tiny brave bird, being fed solitously by its parents. Then to my horror the duck flew down with a thump, grabbed it and tried to destroy it.. Nature raw in tooth and claw… (Duck had brought two broods of ducklings to my garden this year, but All ducklings have gradually disappeared. Now she arrives with 2 or 3 ugly males. NONE are now welcome here..)
I have two questions…I saw a female Mallard being attacked (mating) by several male Mallards. There were several times when she could have flown away. She resisted the onslaught but again, when she could have flown away, she just ran ahead of the males until they jumped on her again. There was no bad ending to this scenario, but I was confused wondering, with several opportunities to fly away, why didn’t she?
2) Do Mallards mate for each egg to be fertilized. or if she lays 1 fertile eggs, does that mean she mated 12 times?
If we assume the female is attempting to lay a new clutch of eggs, she wants to be mated by one of the males. The vast majority of the time, when females are mating, even if there are multiple males, they aren’t injured or killed. So it’s possible she is simply allowing the most effective male to mate with her by seeing who comes out of the pack. This is a kind of sexual selection. Most female birds, including female mallards, can store sperm for some length of time, so mallards don’t need to mate once for every egg. Tom
I had ducks free range on 2 acres for 35 years. I bought them and raised them and fed watered and locked them up every night.. No pond.
I usually had about 20 at any given time. They would divide off into groups during the spring and Summer.mating season! The males from one group would consistently like to rape females from the other group. They were relentless and sometimes two or three males would be on top of one female.
Female ducks willingly mated at times. But only in their own group.
If there were few females and lots of males the males would practically kill the remaining female.mating.bloody her head.peck her eyes. the only way to stop it was to get rid of some of the males. Also sometimes the males would mate with each other if they couldn’t find a female. Yep.
After the ducks molted in the fall they would form a single group and everything was fine. Almost no sex at this time or all winter. All was peaceful for the most part. I didn’t say totally!
I enjoyed having the ducks but they were difficult. I had to lock them up every night or I would lose some. The males were relentless in trying to mate. The females often tried to steal away on a nest. It was hard to find them at night to lock them up. But if I left them out they would be ” Coon bait”