Why are these mallard males beating up this female?

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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.”
  5. 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.


47 thoughts on “Why are these mallard males beating up this female?”

  1. Hi, I overlook a family of mallard – a female and 4 ducklings who are now about 3 weeks old. There is a male usually in close proximity but he doesn’t normally engage with the female in any way. It’s an enclosed courtyard and these are normally the only ducks on the small pond there. Recently 2 males visited and tried to forcibly mate the female – she eventually chased them off. The usual male did nothing to see them off himself, he just walked around close-by while they were doing it – nether helping her chase them away or getting in on the action himself. My question is about this other male – she seems to tolerate him, and when the ducklings were very young he even seemed protective of them – chasing some magpies from their food although he wasn’t eating any himself. Who is this guy? – the father of these ducklings, their brother from a previous year’s clutch, or neither of these options? If he is the father it is strange he didn’t try to help her chase away the other mallard, and if he is not it is strange that she seems to tolerate him and that he does not try to mate with her himself.

  2. We have 8 week old mallards… they love their water dish but wont go swim in our huge pond unless we make them…. why is this?? Will they eventually find the water? Their house we built them is not far from the water ..

  3. It is probably the female’s mate, but mallards aren’t bonded very strongly and most males don’t provide much care for the ducklings. In fact, in most cases, males desert the female after her eggs are laid. If they stick around, it’s usually to try and mate with her if she lays a second clutch. And if other males show up when she is not laying, they don’t seem to care much. The other males, meanwhile, are trying to mate with her on the chance that she is laying. As you can see, mallard drakes are not particularly chivalrous.

  4. Ducklings just want to eat. If their food isn’t in the water and they feel safe where they are, they probably don’t see any need to go to the water … where there might be dangers such as turtles, fish, herons, etc. But I predict they’ll head to the water soon enough. I wouldn’t worry about it.

  5. I just finished building a VERY LARGE pond for my ducks, but they’ve been swimming in one of those little round pools from Wal Mart that I use to water my pig. How come they will not get in this very much larger pond where the water is gin clear as the pool water is often dirty?

  6. Hi Jonah, sorry for the delay in responding. It might very well be that the water in the pond is too clear. What that is green and murky is more likely to have the kind of insects and plants that ducks eat. What do they do in the pig pool? Are they feeding?

  7. No they don’t feed, they just splash around and go under water. The pond is about 3ft deep as the kiddy pool is not even 1ft deep. The pond water has been murky lately so I hope maybe they will start getting in there soon. I also didn’t mention that there is a small group of rocks with water trickling down them on the side of the pond, a small fountain of sorts. Will that keep them from getting in?

  8. Honestly, I don’t know enough about ducks and artificial ponds to know whether a fountain would deter them. I doubt it, but I can’t say for sure.

  9. I feel you left out a lot of information on the Drake. Male mallards (drakes) are very sexually aggressive ducks. They will copulate with other males when a female is unavailable. Also will mate with others species of ducks and have devastated a different species of duck to near extinction.

    I have left a message with a top DNR specialist in Minnesota, to ask if during our MN duck hunting season that only males could be shot. Maybe if this could be done every other year, it may help the female population of mallards and other species of ducks.

  10. Sky, male ducks are certainly aggressive. But I don’t believe it makes sense to view that in the same kind of moral terms with which we judge people. The behaviors of both male and female ducks are the behaviors they have evolved because they work best for them. I’m not sure why you would want to punish drakes for doing what are normal behaviors for them. In terms of devastating other species of duck to extinction, are you talking about the American black duck (Anas rubripes)? If so, I think you are unfairly blaming Mallard drakes. First of all, black duck populations have definitely decreased, but the species is not in danger of extinction, and the main cause for the decline is considered to be habitat loss, not hybridization with Mallards. Hybridization with Mallards is an issue, but even there, that’s not the Mallard’s fault. People have converted large parts of the world to Mallard habitat and we feed them, etc. That has resulted in a growing population of Mallards and an expanding range of Mallards, which has brought them more and more in contact with black ducks with the result being hybridization. So you could blame people just as much as Mallards.

  11. My late friend was a wildlife rehabber and felt that as you said, there was more forced mating in areas that have less vegetation to hide in as in man-made areas. Interesting as birth times we have had wood duck broods, not one duckling was lost due to predation. Interesting… Michelle

  12. Five weeks ago two beautiful drakes landed in our Los Angeles pool and never left. They were around every day and disappeared every night.
    About five times another drake with a fully white neck dropped by and spent the day then took off.
    This morning a hen and 14 ducklings miraculously materialized in the pool. I assume she was in the bushes near by the whole time sitting on a nest.
    While the ducklings are adorable, the behavior of the drakes is not. They are continually mauling the hen. In the water. Out of the water. They are even aggressive to the ducklings. I know they are just trying to forcibly mate but Is this normal with her having just hatched ducklings?

  13. Hi Dan,

    Someone recently asked a very similar question, and I answered it here http://askanaturalist.com/why-are-mallard-drakes-so-aggressive/. The short answer is that if they successfully separate the hen from her ducklings, she may decide to nest again, and then they might father some of her offspring. Tom

  14. Hi Dan,

    Someone recently asked a very similar question, and I answered it here http://askanaturalist.com/why-are-mallard-drakes-so-aggressive/. The short answer is that if they successfully separate the hen from her ducklings, she may decide to nest again, and then they might father some of her offspring. Tom

  15. My pet Peking has been the victim of many drakes. We have a pair, and they started mating a few months ago. This winter we had at least 40 mallards that came to eat, daily. Several of the males mated with her, after they left a few weeks ago, our male roen started attacking her. She has completely rejected her nest. (It’s full, and it’s been days since she’s laid) she also has nothing but scabs on her entire neck. Is she too sick to care for her eggs? Or has she rejected them because of all the unwanted mates?

  16. We have 5 ducks, 4 male, 1 female. We have had them from babies so were unaware of the sexes until they were older. The female has always held her own and if anything was boss of the boys but recently with gtg older I assume, the boys have been forcing themselves upon her and yes its distressing to see. She has also now got small sores on her neck from them. She has laid an egg a night for the about days last month but not sat on any. For the last day or so she has been in the pen sitting quietly alone. A big change from the noisey hungry girl she normally is. Should I pen her away from the boys for a while so she can rest. Whenever she does venture out at least one is trying to mate with her. She seems quiet and very low in the rear. Please help.

  17. I should start by saying that I have zero experience with duck husbandry, so you might want to find a site that specializes in that. Cornell University has a duck health site where you can ask questions: http://www.duckhealth.com/contact.html. I would say, yes, separate her from the males to give her a rest, and in the longer term you might want to find new homes for some of the males. AskaNaturalist.com is really about wild animals — where the balance between males and females is controlled by nature and females can usually escape harassment by moving away. But what I know about keeping animals in captivity, from guppies to cows, says you should always have more females than males for exactly this reason, that too many males and not enough females results in females being harassed by the males — sometimes to the point of death. Also, as I said, I don’t know much about keeping ducks, but I have kept other birds, and I’m wondering whether your female might be “egg bound” (http://www.callducks.net/egg_problems.htm). This can happen to females, especially if they lay too many eggs without enough calcium in the diet. A not quite completely formed egg gets stuck in the formation process resulting in great discomfort. If separating her from the boys doesn’t result in her perking up pretty quickly, you might want to take her to a vet. Egg binding can be fatal, I’m afraid, so I wouldn’t wait too long. Please let me know how it all works out.

  18. I feed the birds, squirrels and rabbits in the winter, and 2 tribes of Mallards have joined the feeding this winter. Not too much fighting, but once spring hit, I have males beating up on females, males beating and dragging males around the yard, and was just wondering if this is ” normal ” mating behavior for the mallard. I also go to the state park where food is not given and have witnessed less fighting than I have around my feeders. Thank you

  19. MemMem, this sounds like spring to me. In male birds, aggression related to mating often increases rapidly at the beginning of the spring. What you’re describing sounds pretty “normal” for mallards in dense populations. At the state park, where the density is much lower, the mallards are in less conflict over space, mates, etc., so there is less fighting.

  20. A couple of mallards have been visiting my yard and swimming in the water on top of my pool cover. Today the female laid an egg just beside my pool on the cement. I am concerned why she didn’t lay the egg in a nest? Is the egg safe out in the open?

  21. The egg is probably not safe out in the open, but I’m not sure there’s much you can do about it. She may be confused by the pool, and eventually, she’ll figure out it’s not a good place to be and they’ll move on.

  22. I do have to agree with Tom. Last year a breeding pair laid a beautiful egg right at the base of the largest bird feeder I have. By midmonth the squirrels and chipmunks and bunnies all visited the egg and feeder all day long. The egg never hatched and I have never run into another egg laid in or near feeders again.

  23. As to your March 24 reply, I did want to tell you that 1 pair is still visiting my yard on a daily or twice daily visit. The male had hurt his foot, it looked nearly torn off to me but if I tried to get close, off they would go and this was at a time they were still fighting with the others. That little female stood next to him like being on guard while he laid and ate, only taking her own food as he was turning and walking away…Every day as much as that leg might have hurt, I could see him getting better and better, today he doesn’t limp much at all and I do expect them to fly the coop any day now. Thank you so much..

  24. I’m sitting at the park right now watching a poor female try her best to get away from 2 male mallards. Being female, I started to feel bad for her. It looked like she was in a bar! Thank you for the explanation. I’ve always wondered why mallards seemed to be so rough about things. Now I know. I love the Internet.

  25. Today I watched and heard a poor female being forced to mate with an attacking male. I tried to ignore it at first, but as she continued to squak repeatedly, I couldn’t stand it and went to her rescue. I managed to scare the ale away, while she scurried off. I know it was probably disturbing the balance of nature, but I just could’nt help myself. Later, I saw the male searching alone for her. I hope she took off far away!

  26. I just witness in our park a female duck not letting a male on top of her so he chased after her and then four other ducks joined in and kept pinning her down under the water. Bitting the the back of her neck. I couldnt watch. But I tryed clapping to try and scare ducks away but it didn’t work. I had to get my kids away didn’t want them to see it.
    would they kill the female ?
    Thankyou for reading this.

  27. I was walking in my park with the children and the dog and I noticed a group of about 15 ducks on the field. I walked away from the ducks because I didn’t want the dog to chase them. He is not that interested in them most of the tome. As I walked on I noticed that they were all male so I knew there was probably a female there too. I left the children with the dog and walked over and could see the female had lost most of the feathers on her head and was bleeding. I chased the males off and her back was bloody and looked sore. She ran off into the hedgerow and nettles. I stood guard to keep the males away and they went off and attacked another female.

    I decided that I had better get the female to a rescue unit and rang the vet. They said that they couldn’t actually do anything but they would look at her. Maybe she would be passed on to a fostering unit. At this point the bird was safely away in the bushes. There were quite a few dogs and there owners walking by so I left her where she was so as not to draw attention to her and we got a towel from the car so we could wrap her up in it and walked around the park but when we got back to where she was she was gone. I felt guilty I didn’t pick her up straight away. She definitely was moving well and had hidden herself so here’s hoping she could recover. I felt a bit sad about it.

  28. Ugh… I’m about to get my young male mallard a female friend. Now I’m not so sure that’s a good idea. He seems pretty aggressive already… though he was never that way with his slightly older male friend. We tried introducing a couple of muscovy juveniles, but the mallard was so mean to them we got rid of them. Any tips on finding him an appropriate friend?

    Also, I’m really having a hard time getting him to enter the duck house each night. He sleeps in the water, hiding in the reeds. We lost 2 other ducks to an unknown predator recently so i’m getting worried.

  29. Kathicka,

    These sound like questions that would probably be better asked of someone who knows about raising domesticated ducks. You could try http://poultrykeeperforum.com

  30. They are just Ducks who are wild. They know Fight or Flee for sure and vary between the two during their lives.

    They are not Being Bad or trying to cause trouble on purpose. Their lives are about finding food and spreading the genetics to the lady ducks. We can learn many things from the wild and the animals who live there.

    Great discussion by the way.

  31. I have been seeing the same aggressive behavior to a female mallard by other males even though she has a mate. Reading these comments helped to explain the reason and made it less upsetting for me to watch. She laid her first egg this morning under the tree where her water tub is. Within hours a big black crow pecked at the egg and it was strewn all over the driveway. If she lays her next egg there, can I move it to a more sheltered spot in the area?

  32. Hi Jan, if you move it, she may not recognize it as hers. Assuming these are wild mallards, you should probably just leave it and let nature take its course. She’ll eventually figure out the best place to nest to deter the crows.

  33. For several years, the same mallard male and female have come to our yard to choose a nest site and she has hatched a successful batch each summer. This year is no exception. She always leaves with her ducklings and stays on the large pond behind our yard. She started with 12 ducklings and is down to 2, which is about typical for her. However, the last few days, 3 males that have been hanging around all winter and spring keep trying to mate with her. (Maybe her previous ducklings? I hope not!) She tries to run away or fly away and sometimes her male partner even chases them off. But in the meantime, her babies are left hiding in the tall grass, alone and vulnerable. Is it possible that these male ducks will try to kill her remaining ducklings to force her to re-nest? She always returns quickly and calls to the babies, but it’s making me a nervous wreck.

  34. Hi Kathy, it is possible that they would deliberately kill the ducklings, but there’s not much you can do about it, unless you want to try and catch the ducklings and raise them. I know it’s hard to watch this kind of carnage on ducklings, and I get the same kind of comments all the time about goslings.

  35. I have noticed also the mallard drakes attacking a lone female.
    At the same time a drake stuck very closely to his family but didn’t hesitate break off to join the attack. We also have a small orphan a little over a week now and always seemingly in the presence of two drakes watching over him. Some drakes protect their mother hen viciously attacking any who attempt to copulate with her.It seems to depend on the drake and his aptitude of husbandry.

  36. I have a fairly large group of domestic ducks, consisting of 15 males and 5 females. We had a lot more females but have lost a few during this mating season. We also keep 5 geese (toulouse) and they share a decent sized enclosure with 2 large ponds. The problem we are having though, is the geese seem to be attacking the female ducks to the point where they are seriously injured or die of shock. Why would the geese be doing this? They leave the drakes alone and don’t attack them. They seem to attack just after forced copulation, so the duck is already in a vulnerable position and cannot easily escape the geese. We are losing a female nearly every week now and don’t know what to do…

  37. Jimmy, I don’t really know anything about how to raise domesticated ducks or geese. This site is about wild animals. So you might want to try site like http://poultrykeeperforum.com/. The one question that comes immediately to my mind is what they sex ratio of the geese is. Do they have females to mate with? Male animals will sometimes try to mate with other species and even inanimate objects if they don’t have opportunities for mating with their own species.

  38. I’ve noticed that the pond in the neighbourhood had both male and female ducks at the beginning of spring, now, it seems that there are only females left. what’s up?

  39. Male mallards molt earlier than females and molt into coloration that is very similar to females, so what you might be seeing is females and molted males. Check out the “adult male in eclipse” in this illustration: http://www.washingtonpost.com/wp-srv/special/metro/urban-jungle/pages/110830.html.

  40. We have a creek by our home, and normally there is a fairly even number of males and females, before and after mating and birth. This year, after birth of several batches, there is only (1) male, and about 100 females since Spring. What’s going on?

  41. Hi Larry,
    This time of year, the males molt into coloration that looks very much like females. Check out this illustration: http://www.washingtonpost.com/wp-srv/special/metro/urban-jungle/images/mallards.jpg

  42. Is there any sex order in the hatching? The first hatched duck would imprint on the adult female but subsequent hatchlings should imprint on both the adult female and the other hatchlings, should they not?

  43. Hi – I live in Christchurch New Zealand, and I have noticed over the 35 years I have lived beside the river, that in the last few years (since our bad earthquake) the ducks have become more and more aggressive towards each other. Today for the first time I saw a female duck attack a mother duck who was trying to enter the river with her 13 ducklings. She had already been attacked by a drake and was weakened. She lay down and let the other female sit on her and peck her neck over and over. Eventually the attacker stopped and the mother and her babies waddled up a drive way. It seemed really territorial but I don’t know if mallards are territorial or not. We have a couple of native ducks (paradise and papango) that live in the river as well and they never seem to attack each other. They mate for life, and the males stick around protectively. I find it really hard to watch the mallards, but I wonder if something has changed since the earthquake that has make them so aggressive suddenly.

  44. Hi. I don’t know whether an earthquake could change the behavior of ducks. As for one female attacking another, one possibility is that the female attacker is not a female, but a male who has molted into non breeding coloration and is maybe just starting to come back into breeding hormones and hasn’t yet molted into breeding colors. When in their non breeding coloration, males look very much like females.

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