Kees Moeliker, emceeing Dead Duck Day in 2016.
Kees Moeliker, emceeing Dead Duck Day in 2016. All photos: Kees Moeliker

On June 5th, 1995, at around 5:55 PM, Kees Moeliker, the director of the Natural History Museum in Rotterdam, was finishing up his workday when he heard a loud, reverberative thud. He went and looked out the window. Below, on the grass, was a dead male duck, recently felled by the the museum’s brand new, glassed-in wing.

Nearby was a live duck, also a male. As Moeliker watched, the live duck mounted the dead one and started copulating with it.

Male ducks are known for their aggressive sexual behavior—they’ve got long, spiky penises, and often force themselves on unwilling females. But before Moeliker, no one had ever observed this particular act. And so every June 5th since then, for 22 straight years, Moeliker has held a small ceremony at the scene of this unique crime. He calls it “Dead Duck Day.”

The two ducks that started it all.
The two ducks that started it all.

The Dead Duck Day gathering happens right outside the museum. It generally lasts for 15 or so minutes, from 5:55 PM to about 6:10. Moeliker opens by showing everyone the dead duck in question—now stuffed, and part of the museum’s collection—and saying a few words about its fate.

He then talks about other, more recent examples of unusual animal behavior. There are guest speakers and moments of silence, and some years, bonus events: last year, there was a fashion show. In 2013, Moeliker unveiled a new addition to the museum itself—a splatter-shaped memorial on the outside wall where the duck hit, along with an explanatory plaque below.

How about this year? “It was a success,” Moeliker says over the phone, as he walks with fellow attendees to a local restaurant for the traditional six-course, post-ceremony “duck dinner.” “We had about 85 spectators—it was a record. And the weather, as usual, was beautiful.”

Last year's Dead Duck Day crowd gathers around the fateful spot, now commemorated by a splat.
Last year’s Dead Duck Day crowd gathers around the fateful spot, now commemorated by a splat.

Why would one duck treat another this way? We do not, and cannot, know. Why would a growing group of humans commemorate it? That one is easier, though only slightly. In Moeliker’s own words, the experience has changed his life. In 2001, he published a paper, “The first case of homosexual necrophilia in the mallard Anas platyrhynchos,” in the museum’s journal, Deinsea. Two years later, that paper won an Ig Nobel Prize, the annual award for offbeat-yet-consequential scientific research.

People started flooding him with other surprising animal behavior tales, bringing him community and a certain measure of fame. “If there’s an animal misbehaving on this planet, I know about it,” he said in 2013, while giving a TEDTalk about his experiences.

Moeliker is doing his best to pay it forward, using Dead Duck Day and other appearances to raise awareness about how dangerous glass windows are to birds. “We decided to commemorate the tragic fate of this particular duck,” he says. “But in fact, we commemorate all those billions of birds that died in a similar way.”

The Rotterdam Natural History Museum's new special-interest duck specimen.
The Rotterdam Natural History Museum’s new special-interest duck specimen. All photos: Kees Moeliker

As of this year, that includes one bird that also had a similar post-death. During today’s ceremony, Moeliker showed the crowd a brand new museum acquisition, which a fellow naturalist sent him this past spring. “It’s the second documented case of homosexual necrophilia in the mallard,” he says. “Some people have been waiting for this for 22 years.” At least one person, anyway.

Naturecultures is a weekly column that explores the changing relationships between humanity and wilder things. Have something you want covered (or uncovered)? Send tips to