As It Happens

Ne'crow'philia: Why crows sometimes fornicate with the dead

Kaeli Swift, a PhD candidate who studies crows, caught the odd behaviour on film.

Researcher who filmed the bizarre act said it was 'incredibly surprising'

Kaeli Swift captured this image of a crow mating with a dead crow. (Kaeli Swift )

When Kaeli Swift laid a dead crow next to a cherry tree, she was hoping to capture the oddity of a crow "funeral" on film. What she got instead was a crow attempting to mate with the dead.

"We were incredibly surprised," Swift, a PhD candidate who studies bird behaviour at the University of Washington, told As It Happens guest host Laura Lynch.

In April 2015, Swift was doing an experiment to try to figure out why crows are so interested in other dead crows.

In her first study, Swift had already observed crows conducting "funerals" — congregating around their dead peers and sending out alarm calls. She said they likely to this to warn of potential danger.

Swift believes that the crows mate with dead crows during the breeding season because their hormone levels are so high. (Kaeli Swift)

She was hoping to capture this ritual on film, but this particular crow was not interested in mourning the dead.

Just a few moments after Swift laid the dead crow on the ground, the living crow swooped down to inspect the corpse.

"Instead of alarm calling right away, it flew down to the ground and started to walk up to the body," Swift said.

"I had seen this happen before. Sometimes they like to get really close and really inspect before they start alarm calling and take off the sky."

Started to strut

Instead, this crow dropped its wings, erected its tail, started to strut — and mounted the dead crow.

Like most birds, crows do not have penises and do not perform penetrative sex. What they do instead is rub their cloacas — which are like vents under their tails — together. 

The crow continued to attempt to mate with the cadaver until another crow came along and started the alarm call.

Swift said it's not unheard of for animals to copulate with other dead animals, but she had never heard of it in crows.

So for the next three summers, she studied hundreds of crows to find out more about this behaviour.

Her findings were recently published in The Royal Society Journal.

Using a lot of cadaver crows, Swift said she would find pairs of crows that were breeding, place a dead crow near them, and wait.

'Rip these birds to shreds'

What she found was the majority of the crows would just let out an alarm from afar. Some of the crows would touch the cadaver, and then a very small amount  — around four per cent  — would try to mate with it.

Swift also observed that some of the crows would viciously attack the corpses and "rip these birds to shreds"

Swift points to the time of year for why the crows engage in this odd behaviour. April is the beginning of breeding season — so the crows are particularly libidinous.

Swift studies bird behaviour at the University of Washington. (Submitted by Kaeli Swift)

"It's sort of a tortured analogy, but it's kind of like that feeling of calling your ex at three in the morning," Swift said.

"Your prefrontal cortex, it knows it's a bad idea. It knows that this isn't the right way to respond. But it's three in the morning."

In the crows case, Swift said they know what they are doing isn't productive.

Rather, she said, they just can't help themselves.

Written by Sarah Jackson. Produced by Samantha Lui.