This Week in the History of Sex: Homosexual Necrophilia in the Mallard Duck

Twenty-seven years ago this week, something unusual took place in the Netherlands: an observational study of the world’s first known case of homosexual necrophilia in the mallard duck.

Yes, you read that sentence correctly.

Kees Moeliker, the curator of the Natural History Museum of Rotterdam, looked out the window after hearing a loud bang, where he saw a duck on the ground that had died after flying into the window. Another male mallard came over and attempted to copulate with the corpse. Moeliker documented the event (which lasted for about 75 minutes) by taking notes and photos, and then collecting the corpse for later examination. He eventually published an academic report about his findings.

As Moeliker discusses in the video below, this chance observation changed the course of his life and career. His study attracted a lot of attention, and people started sending him photos and videos of other animals engaging in seemingly unusual sexual behaviors (including more necrophilia, cross-species copulation, and animals attempting to mate with inanimate objects).

So what’s behind these behaviors? That’s a mystery Moeliker is still trying to figure out. He has some theories (discussed in the video below, and also in this write-up of the original study I did on the blog several years ago)–but one additional theory that could help to shed some light on this is that much of this behavior may be driven by skewed sex ratios and/or lack of other mates in the local environment.

For example, in a study of tortoises I previously covered on the blog, researchers looked at the mating behaviors of male turtles on different parts of an island where the sex ratio naturally varied (in some parts of the island, 1 in 5 turtles are female; in other parts, just 1 in 20 are female). What they found was that in parts of the island with more heavily skewed sex ratios (meaning males outnumber females by a wider margin), males exhibited more diversity in sexual behavior. This included not just more same-sex behavior, but also more instances of necrophilia–and even some recorded attempts to mate with stones that looked a little bit like they could be turtles.

On a side note, Moeliker commemorates the day of his observation (June 5th) each year with a series of events in the spot that it occurred. He has unofficially dubbed it “Dead Duck Day.” Click here for a look at the history of Dead Duck Day and previous events (although note that all celebrations have been postponed or have gone virtual since the onset of COVID-19).

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Image Source: iStockphoto