How Do Birds Mate?

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Kingfishers Mating
Image by Jonus Weng Via Flickr.

Backtrack to 1999, arguably one of the best decades for music, and you may remember a song by Bloodhound Gang? 

I spent many a day blindly singing “do it like they do on the discovery channel”. 

Of course, back then I didn’t really know what the phrase meant. 

Fast forward 25 years and, well, need I say more?

The song, unfiltered though it may be, refers to the intimacy of sex; in its own animated perspective. 

It shouldn’t be a shock. Most animals have sex; or, to be scientifically correct, mate. It’s a way of reproducing and passing on genes. 

But not every animal group exhibits the same mating behaviors. 

This article aims to explore the unique world of how birds mate.

Evolution of Bird Mating 

To understand how birds mate, we need to first travel back in time. Over 120 million years ago, to the late Jurassic period. 

During this time, one group of reptiles dominated the land – the dinosaurs. 

These egg-laying reptiles had a specific anatomical feature that facilitated egg laying – the cloaca. 

Obviously something worked with the cloaca because, fast-forward to the present day, and birds still use their cloaca in much the same way as their reptilian ancestors would have. 

The Function of the Cloaca

The cloaca. 

We’ve just found out that dinosaurs used to have one. 

But what exactly is it? What does it do?

What is a Cloaca?

The cloaca is a multifunctional opening found in birds, reptiles, amphibians and even some mammals. 

It is an opening for the digestive, reproductive and urinary tracts, found just below the tail. 

The Cloaca of a Wagtail
Image by Tim Melling via Flickr.

Function of a Cloaca 

The cloaca has multiple functions – the ejection of feces, urine, eggs and sperm.

Unlike mammals, which often have external genitalia in the form of a penis (male) and vagina (female), the sexual anatomy of birds is remarkably different. 

Sexing birds from the exterior alone poses quite a challenge, as both males and females possess a cloaca. 

The structure of the cloaca in both males and females are similar. However, during the bird mating season, many males may see an increase in the size of their cloaca. In some instances, this size increase can mean the male cloaca often protrudes from the body. Scientists have hypothesized that this may help with sperm transmission via deep insemination. 

Some species, such as the inca dove, use their cloaca for unconventional methods. 

Their native range of Central and South America can get hot. However, like most other bird species, Inca doves cannot sweat to cool down. 

The solution? 

As an emergency tactic for thermoregulation, the Inca dove can use their cloaca to actively cool themselves down. 

By exposing, and I can’t believe I’m writing this, the moist lining of their cloaca to the air, enough water is evaporated to regulate their temperature. Strange.  

Do Birds Have Penises?

Most birds have a cloaca. We’ve established that.

But what has happened to the penis? Do birds even have penises?

Astonishingly, upwards of 97% of known bird species do not have a penis. However, that still leaves 3% of bird species with a penis, right?

We’ll come back to these 3% later. 

First, let’s look at penisless birds. What happened?

After a lot of research, scientists have discovered that many bird species possess a specific protein that suppresses the growth of genitalia during development. 

There are many speculations as to why. 

Perhaps females actively selected males with a smaller penis. By choosing males with smaller phalli, a female can gain more control over reproduction. A potential way to counter the prolific rate of infamous duck raping behavior. Again, more on that shortly.

Other theories suggest the loss of genitalia is a side effect of other changes within a birds’ body. Proteins that control feather and beak shape may have influenced the lack of development in other areas. 

Who knew penises could be so complicated?

How Birds Mate

Now that we have an understanding of the anatomical features used by birds to mate, let’s take a look at the nitty gritty of how a bird actually mates. 


Northern Cardinal Courtship
Image by David Hawkins via Flickr.

First up, courtship. 

A form of communication, courtship displays in birds are a way to signal their readiness to mate. 

Across much of the bird world, it is the males that perform intricate courtship displays; either in the form of dance, color or noise. 

The purpose?

Well, to impress a female. Simple as. 

Female birds invest a lot of energy in producing and incubating eggs, as well as raising chicks. They need to be sure that the partner they choose will produce healthy offspring. 

Birds-of-paradise, for example, use brightly colored plumage to court a female. Males with less colorful feathers may be suffering from stress-induced illnesses, such as increased parasite loads. 

Other species, such as the Northern mockingbird, use songs as a form of courtship. Males that can perform more song variations are likely to mate with more females. To a female, a male that has a range of vocalizations shows longevity and experience of raising chicks. 

The Cloacal Kiss

Right. A male has impressed a female. He’s in. 

What’s next?

Well, this is where the cloaca comes in. 

For the vast majority of known bird species, after some form of courtship (behaviors to attract the opposite sex) the male mounts the back of a female. 

Lark Sparrows Mating
Image by Jerry Ting via Flickr.

With the back of the female slightly arched, and any tail feathers moved aside, the cloacas of the two sexes meet. The connection of the cloacas, romantically referred to as the ““cloacal kiss”, allows for sperm to be deposited from the male to the female. 

Scientists studying the intimate world of bird sex predict that just 1-2% of sperm make it into the female. Because of this, it isn’t uncommon for birds to “kiss” multiple times in a given session.  

So, although the cloacal kiss itself lasts mere seconds, the act of balancing atop of one another, and the multiple mating attempts, means that some bird matings can last up to a week to increase fertilization success. 

Once sperm has been transferred, the act of internal fertilization – the fusing of sperm and egg inside the female’s body – can begin. 

What Happens After Birds Mate?

After birds mate, sometimes a male will leave. He will have no further input in nesting or raising chicks. 

However, many bird species are monogamous. A male and female will remain together – either for the duration of a breeding season or a lifetime. 

Together, they will take turns feeding chicks until the chicks are old enough to leave the nest.

Birds With Penises

I said I’d come back to it. 

How could I not?

Just 3%, or approximately 300 species, of birds have a penis – or, technically speaking, a phallus (this sexual structure evolved independently to the mammalian penis, so cannot be called as such). 

The males of two groups of birds, ratites (ostriches and emus) and waterfowl (ducks and geese), have long and flexible phalli that emerge from their cloacas during mating. 

Let’s take a look.


Unassuming though they may look, do not be fooled. 

Some ducks, such as the lake duck, have a tentacle-like phallus as long as their entire body – sometimes reaching half a meter in length. 

Wood Ducks Mating
Image by Matthew Studebaker via Flickr.

Other ducks, such as the Muscovy duck, have equally impressive genitalia – up to 40 cm long.

But why so big?

Well, like many other birds, female Muscovies choose their mates based on his courtship and plumage displays. However, males that fail to live up to the females standards don’t simply give up. 

Having a long, and flexible, sexual appendage helps males force copulation on unwilling females. And, to speed things up, a male duck can obtain an erection, or eversion, in just a third of a second.

To overcome this, female ducks have evolved a labyrinth of twists, turns and dead-ends within her vagina to prevent unwanted fertilization. An ongoing evolutionary arms race of the sexes. 


The ratites are a group of flightless birds that include ostriches, emus, rheas and kiwis. 

Like ducks, all male ratites have a phallus. 

Unlike waterfowl, however, which have a corkscrew-shaped phallus, the phallus of a ratite is conical in shape. 

However, not all ratites share the same size phallus. 

Take the ostrich. When mating, the male male will allow the flow of lymphatic fluid into the phallus, increasing their size from 20 cm to a whooping 40 cm. 

For the record, and to keep us guys from getting too disheartened, the average human penis is in the 12 cm – 17 cm range. No shame, fellas. 

However, scientists have discovered that there is a strong correlation between genital size and bird mating habits. Ratite species that pair bond, such as emus, have smaller phalluses, compared to their more promiscuous, and well-endowed cousins, the rheas. 

Final Thoughts 

Heron Courtship
Image by Pedro Lastra via Flickr.

Bird mating is intricate. 

From complex courtship displays to brief cloacal kisses, there is more to bird mating than meets the eyes. 

And then there’s the phalluses. The rape. The passages that lead to nowhere. 

The world of avian mating is an interesting one, albeit a bit strange. Best we’d leave it to the experts. 

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