Discover Why Ducks Have Genitalia In the Shape of Corkscrews

The animal kingdom is full of strange and incredible facts. When it comes to procreation, some animals have much more wild habits than others. Take, for example, the barbed penises of large felines, or the sexual cannibalism that sometimes occurs in black widow spiders. Not all mating dances are enjoyable, in fact, many are brutal activities that exist only to ensure the future of a species. As it stands, there are only a handful of animals that actually have sex for pleasure. Ducks do not have sex for pleasure, as far as we know, but they do have some really interesting breeding habits. Today, we’ll be looking at one of the strangest aspects of duck copulation – the actually sexual organs they use. We’ll be focusing on the phallus of the male duck – a corkscrew-shaped penis that serves an interesting purpose.

The Anomaly of Ducks

We think it’s important to point out that most birds do not breed via penetrative sex. In fact, about 97 percent of birds mate by simply rubbing their cloacas against one another. A cloaca is defined in zoology as “the common cavity into which the intestinal, urinary, and generative canals open in birds, reptiles, amphibians, many fishes, and certain mammals.” Female birds also lay their eggs by passing them through their cloacas. Without penetration, these birds are still able to pass male sperm to female ova and successfully achieve fertilization.

Ducks, however, use a much more aggressive and penetrative form of sex for fertilization. Let’s start by taking a look at the genitalia of both male and female ducks. Then, we’ll explore how – and why – this mating ritual works.

Genitalia of Male Ducks

A male duck is called a drake. Drakes have a corkscrew-shaped phallus that grows to a variety of lengths. The length of a duck’s penis is dependent on the environment. Specifically, a flock of ducks with a higher number of drakes yields ducks with longer penises – some of them up to 18cm in length. The longest avian penis belongs to a South American duck, the lake duck, and reaches insane lengths. In fact, this variety of ducks has the longest penis in relation to body length out of any vertebrate in the world. The longest-recorded duck penis was a lake duck in Argentina, which boasted a total length of 42.5 centimeters. That’s 16.73 inches in length. For comparison, the average human erect penis is between 13 and 18 cm or five to seven inches in length.

The phallus of a duck is knowns as the “true penis”, and only domestic birds such as chickens, turkeys, ducks, and geese possess them. Most other birds do not have a phallus and have other means of copulation. The phallus of a duck is usually flaccid and coiled along the ventral wall of the duck’s cloaca. When erect, the phallus bursts forth from the cloaca and extends to its full length. Studies suggest that the phallus of the drake does not become erect due to muscle tissue. Instead, the phallus is ejected outward by a buildup of fluid inside the cloaca. This means that the process of reproduction has to happen very quickly, as there is no blood or muscular tissue to support the drake’s phallus.

Genitalia of Female Ducks

A female duck is either called a duck or a hen. Hens have developed an interesting reproductive system in response to the corkscrew-like phalluses of drakes. The vaginal tract of a hen is actually designed to be hard to penetrate. Most female birds that breed via penetrative sex have a simple and tube-like oviduct, which makes breeding very simple and straightforward. Hens, however, have a completely different set of reproductive tools. The oviducts of hens are spiraled and full of crevices and sacs that enhance their complexity. Some people refer to female ducks as having “labyrinthine vaginas”. The oviducts are shaped in a clockwise spiral with a number of “blind pouches” along their lengths.

How do Ducks Breed?

A lot of breeding in ducks is in the form of forced copulation. This is, in fact, why female ducks have such complex vaginas. The oviducts of hens are designed in an evolutionary “arms race”. What do we mean by that? This is a very strange example of survival of the fittest. A study on the sexual morphology of ducks by Dr. Patricia Brennan and colleagues reveals that female ducks have coevolved with drake penises as a result of antagonistic sexual conflict. The study tested drake ejaculation in a variety of settings similar to and separate from the actual shape of a duck vagina. They found that drakes were highly successful in depositing their sperm into straight tubes and counterclockwise spiral tubes. However, when the drake was presented with a tube that mimicked the genitalia of a hen, the success rate dropped.

As we mentioned before, the process of drake ejaculation is very fast. The corkscrew-like phallus – sometimes compared to a protruding tentacle – bursts from the cloaca and enters the hen’s oviduct. The complex oviduct is hard to penetrate and inseminate. This is an evolutionary result of the forced copulation of waterfowl. Once the drake has successfully penetrated the oviduct and released his sperm into the correct channel, the insemination and fertilization are complete. The process only takes a couple of seconds from start to finish. Let’s look at why this is such a complicated task.

A Response to Forced Copulation

Because any adult drake can attempt copulation with any hen, evolution has helped the species maintain its standards of strength and virility by creating environments where the fittest ducks have the highest reproductive success. We observed earlier that flocks of ducks with higher drake populations yielded drakes with longer phalluses. This is part of the competition for genetics. The fittest and largest ducks with the longest phalluses are often the most successful at copulation, which helps to ensure strong lineage and stability in duck species.

A hen’s vagina is specifically evolved to fend off mating attempts from biologically inferior ducks. The twisted shape and false pockets of the oviducts help to keep lesser ducks from fertilizing the hens. This is a clever response to forced mating rituals that give the hens a certain level of control. Drakes evolved, too, of course. The question of why a male duck’s penis is shaped the way it is can be answered the same way as the question of the hen. A long, flexible penis increases a drake’s chance of fertilizing a hen and passing on his strong genetics. It seems that ducks quickly adapt to their surrounding and evolve or adapt quickly to face the challenges of their environments.

Summary

Learning about the mating rituals of ducks isn’t necessarily a fun task. The idea that forced copulation has led to a complete change in the reproductive systems of both male and female ducks is a strange one to grasp, especially as a species of animal that relies so heavily on consent. It’s true that we have little we can relate to ducks in terms of personal experience. Humans have not yet evolved physical attributes that are meant to repel the advances of unwanted copulations, but ducks have.

Drakes have evolved long, spiral phalluses that work to ensure reproduction through forced copulation. Hens have developed complex and labyrinthine oviducts to maintain some control of reproduction and ensure a positive result for the whole species. Most species that rely on forced mating have evolved physical structures for repelling unwanted advances and ensuring the health and virility of their young.