Can Ducks Switch Genders? You Won’t Believe This… 

You hear about some pretty strange lore concerning ducks and other poultry when you hang around the scene long enough. Tales of drakes laying eggs, flocks consisting of nothing but hens suddenly producing ducklings, and more craziness besides.

four Pekin ducks
Can you tell the genders of each of these Pekins?

It’s easy to roll your eyes at such things, but now and then you’ll talk to people who know their stuff, or even read new stories about it. It’s enough to make you wonder: is it possible for ducks to switch genders?

Yes, though this is not a voluntary action on the duck’s part. Female ducks may start to exhibit male characteristics in the form of plumage color and pattern, behavior, and growth rate if their ovary cannot produce enough estrogen for whatever reason.

Let me tell you, I just about fell out of my chair when I found out this was actually true. And it’s not from a mountain of anecdotal evidence either: science has confirmed it in numerous studies.

It’s very rare, and you should still take most tall tales like this with a grain of salt, but it is not at all impossible. Prepare for the unexpected, keep reading, and I’ll tell you all about it down below!

How is it Possible for a Duck to Change Genders After Birth?

Through a quirk of biology, specifically bird biology. And before you ask, yes, the sex of a bird is determined at birth and it’s determined by the egg, unlike by the sperm in mammals.

That said, if things go wrong concerning the sex hormones after a duck has reached adulthood, it will start to change genders into the opposite, specifically from female to male.

A Brief Primer on Bird Genetics

For any of this to make sense, we’ve got to have a quick primer on bird genetics. I promise, I won’t go too far into the weeds and I will keep this quick. But without this information, the following just won’t make sense…

If you know anything at all about human genetics, you know that we have two chromosomes that determine our own sex: XX for females, and XY for males.

It works similarly in birds, including ducks, but there are some significant changes. For starters, birds use Z and W chromosomes. And this time, the distribution is flipped: males are ZZ, and females are ZW.

These chromosomes are assigned by the egg inside the hen, getting assigned either Z or W. Then the sperm from the male comes along and produces the second chromosome, another Z.

I promise this will be important throughout, bear with me. And buckle up, because this is where things get interesting…

Ducks Can Actually Select Which Sex an Incubating Duckling Will Be!

What’s highly remarkable about the reproduction of birds, including our ducks here, is that, somehow, females are able to manipulate, determinatively, which chromosome they puts into an egg.

Because the sperm of the male duck is always going to supply a Z chromosome, the female is calling the shots on whether or not an egg will hatch as a drake or a hen.

To this very day, scientists aren’t quite sure how birds are able to do this, though there are indicators in different species: in finches, for instance, lean times and resource scarcity lead females to select more eggs to be female.

Other species tend to first produce a male egg and then switch to a female egg for successive generations. It’s all still a mystery!

And recall from the previous section that a ZZ chromosome is a male; it is the introduction of a W chromosome that will yield a female- meaning the baseline for bird biology is male.

We see this early in embryo development where additional genes interact with a ZZ embryo to start the development of testes. The same gene, in a ZW embryo, causes the testes to develop into an ovary instead.

This is important because sex hormones, testosterone, and estrogen as expected, are crucially important to the development of the sexes, but also play a huge impact in the ongoing biology of a bird.

If a Female Duck Can’t Produce Enough Estrogen, a Change Takes Place

If the left-side, functional ovary of a female duck malfunctions, is damaged or in any way can’t produce enough estrogen, the testosterone imbalance will start to change her!

Though she nominally has an ovary on the right side, it’s basically dormant and not responsible for producing the sex hormones for females!

Accordingly, when that left-side, estrogen-producing ovary malfunctions, the one on the right will respond by turning into a sort of proto-testis, and begin producing testosterone as normal for a male duck!

This, of course, plays havoc on a duck’s system and leads to growth, behavioral, and physical changes: she’ll develop a stereotypical drake curl in her tail feathers, the color and pattern of her plumage will begin to change, she’ll put on more muscle and get more aggressive.

Her quack or vocalization will even take on male characteristics, though a total change is rare depending on the breed.

This poor, sex-confused duck might even try to breed with females, and will fight with other males and police the flock as drakes tend to do.

This is, in essence, the gender change that sometimes happens in ducks: a sudden loss or precipitous drop in estrogen leads to the development of male sex organs which will produce testosterone.

What Causes a Hen to Stop Making Enough Estrogen?

The next obvious question is what causes a hen to stop making estrogen? As mentioned, only her left side ovary is responsible for the production of this critical hormone.

Any number of things could interfere with estrogen production, including old age, sickness, genetic defects, and sometimes even physical injury which directly damages the ovary.

Even severe calorie deficits or nutritional imbalances can cause a drop in estrogen production, but by then typically the health of the duck is compromised, and sudden changes are less likely to occur or be noticeable.

Basically, it’s almost invariably the result of something bad happening to the duck.

Do Changed Female Ducks Act Differently?

Yes, they do! They tend to act more like drakes. They usually get a bit more standoffish, more aggressive, and are more eager to fight with what they see as their fellow males. As mentioned above, the changed female might even try to mate with other females!

Basically, whatever is typical behavior for a male of a given breed, you should expect to see more behavior like that out of an affected female.

Can a Female Change to a Male Duck and Back Again?

Even more strangely, yes she can, sometimes!

Although this is even rarer, owing to the likely causes of the change in the first place, it is nonetheless possible.

However, it’s only likely if there is already a major hormonal imbalance in the duck’s body that can be corrected over time with supplements, medicine, or a better diet, or else if there is an infection in the ovary that might compromise its ability to produce estrogen.

Once the duck is healed of the illness, or the hormonal balance is corrected, she should go back to normal. If she has already started to develop male plumage and other features, these will dissipate and revert over time.

Are Ducks Ever Born with an Indeterminate Gender?

Yes, but very rarely. Like, once in a blue moon rarely!

Interestingly, these intersex birds are typically referred to as chimeras and can be quite spectacular in appearance, having a front-to-back asymmetry that is split right down the middle, appearing male on the right side and female on the left side.

If you’ve been paying attention, you might have noticed that that is the sides that correspond to the male sex organs and the female sex organs inside the bird’s body.

This means you might spot an intersex duck, particularly one that shows high sexual dimorphism in physical appearance, and looks completely different on one side from the other! Have a look at this chicken for an example.

Can You Prevent This Gender Change from Taking Place?

Nominally yes, assuming you know what’s happening and can administer hormones to the affected duck. But assuming that isn’t on the table then there’s nothing you can do to stop it, but it’s not necessarily something you need to stop, either.

More than a few duck owners have dealt with this issue, and assuming your duck is in good health overall otherwise, they can go on to lead normal lives, though obviously, this will be a major problem if you are depending on that girl for egg production because she will usually stop.

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