Capitol Hill Aviary | Hill mallards embroiled in battle of the sexes

Now that spring is on its way, it’s time for us at Capitol Hill Aviary to talk about duck sex. Like virtually all animals, birds spend a great deal of energy on reproduction. Many ducks — including the mallard, a common water bird around the Hill — have an unusually violent reproductive strategy.

Male mallards, as you may know, have bright green heads and mustard-yellow bills. Females are mostly brown, with some muddy orange on the bill and a patch of blue on the wing.

Mallards typically form pair bonds in the late fall or early winter. By March or April, the female chooses a nest site, and the pair grows increasingly territorial.

Several times per day, either the male or female signals interest in copulation by pumping their heads up and down (which looks totally sexy if you happen to be a duck).

During copulation — which lasts just a few seconds — the male mounts the female, grasps her neck feathers with his bill, and thrusts. His phallus is not usually visible, but it is up to eighteen centimeters long and shaped like a corkscrew, with a groove along the outside for delivering semen.

People sometimes say mallards are monogamous, but most mated males seek opportunities to copulate with females that are not their mates. This is not unusual in the world of so-called monogamous birds—but in most other bird species, males and females appear to be equally willing participants in these encounters. Among ducks, females usually resist the attentions of males that are not their mates.

When approached by a non-mate male, a female mallard attempts to fly away, hide, or dive underwater. If her mate is nearby at the moment, he attempts to defend her—but other males may attack in groups and overwhelm him. Then, by turns, they engage in a behavior that biologists call “forced extra-pair copulation.” Laypeople often just call it rape.

These episodes are so violent that female mallards are sometimes badly injured in their attempts to get away. After it is over, they generally face—and resist—and fail to repel—immediate copulation attempts by their mates. Biologists call this “forced pair copulation.”

From a biological perspective, the male mallards are following their instincts to produce as many offspring as possible. And genetic studies show that a small percentage of baby mallards are indeed fathered by males that were not the mother’s mate. However, the males’ reproductive strategy has been partially thwarted by peculiarities of the female ducks’ anatomy.

A 2007 study of duck genitalia showed that in mallards and many other species that engage in forced extra-pair copulation, the females’ vaginas have many forking dead ends. Biologists believe that female ducks can direct an attacking male’s phallus toward a dead end, thus making the whole event much less likely to end in reproductive success. They hypothesize that male and female ducks’ genitalia have coevolved to grow longer and more complex as each sex attempts to gain a genetic advantage over the other.

Mallards mate while swimming, so if you want to see (or avoid seeing) them in action, they’ll be on all of the decent-sized bodies of water around the Hill.

Hummingbird update
In other bird sex news, I saw a male Anna’s hummingbird performing its mating display in mid-February this year. There’s sure to be plenty of hummingbird displays around the Hill throughout March and April. The best way to find one is by ear: if you hear an unusual, high-pitched chirp repeating over and over, look up.

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Melissa Koosmann is a freelance writer and resident of Capitol Hill. She writes about education, culture, and nature — and, sometimes, birds for CHS.

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