As It Happens

These bold little birds snatch the hairs off living mammals to use in their nests

Scientists in Illinois have published a new study about “kleptotrichy,” a phenomenon in which little birds boldly pluck hairs off of living mammals, including racoons, dogs, humans and even cats.

‘They are definitely endangering their lives by doing it,’ says scientist

A tufted titmouse watches as a raccoon gorges on a downed bird feeder in Prince Frederick, Md. A new study has found the little birds will sometimes steal the fur off living animals, including raccoons, to use in their nests. (Linda Davidson/The Washington Post/Getty Images)

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The first time Mark Hauber saw a video of a teeny tufted titmouse ripping the hairs out of a live animal's back, he thought: "This is dangerous."

Hauber is the lead author of a new study on "kleptotrichy," a phenomenon in which little birds boldly pluck hairs off of living mammals —  including raccoons, dogs, humans and even cats — and weave them into their nests.

"It just reminded me of birds walking in the open mouth of crocodiles, and sort of endangering themselves by hiking on giraffes," Hauber, a professor of evolution, ecology and behaviour at the University of Illinois Urbana-Champaign, told As It Happens guest host Katie Simpson.

"They are definitely endangering their lives by doing it."

The study about the daring bird manoeuvre was published last week in the journal Ecology.

Hauber first came across the phenomenon when his co-authors, Henry Pollock and Jeffrey Brawn, were doing a spring bird count in central Illinois and happened upon a tufted titmouse plucking pieces of fur from a sleeping raccoon.

Scientists already knew that mammal hair is commonly found in birds' nests but had assumed it was collected from carcasses or shedded fur.

"This was from a live raccoon with claws and teeth. And the raccoon didn't seem to mind because it didn't even wake up," Brawn said in a university press release.

When the scientists looked into it further, they discovered there was almost no scientific literature about the behaviour. But there were dozens and dozens of YouTube videos.

"There's about nine times more mentioning of this phenomenon on YouTube than in the scientific literature. And that's, you know, great credit to our bird watchers and nature enthusiasts all around the world," Hauber said.

One clip shows a tufted titmouse furiously ripping the fur from a sleeping dog, which doesn't seem to even notice. Another shows a titmouse landing on a woman's head and making off with a few strands of her hair

One YouTube video shows a bird plucking the hair off a raccoon's back, until the raccoon gets annoyed and takes a swipe at it. But the determined bird simply dodges the blow and returns to its business.

As far as the scientists can tell, there's nothing in it for the victims of this hair-snatching.

"There's really no other explanation here because it doesn't look like these chickadees are plucking lice or ticks out of the fur," Hauber said. "They are going for the fur itself."

So why do the little birds take such a big risk? Hauber and his colleagues don't know for sure, but they have a few ideas.

A nest insulated with fur might help protect baby birds from the cold weather. Or perhaps the scent of fresh mammal hair wards off would-be predators.

"And then finally, we know that a bird's nest often have lice and mites that chew on feathers," Hauber said. "And so, you know what? If you could misguide those mites and lice by having them chew on this mammalian fur instead of your nestlings feathers."

Whatever the reason, Hauber says he's hopeful the study will be a starting point for further research.

"There's probably 15 other alternative [reasons] that I haven't thought of and we haven't mentioned in the paper," he said. "The next step is experiments to go out and ask the questions: Why are birds putting themselves at risk to put fur from live animals, live mammals, into that nest?"

Written by Sheena Goodyear. Interview with Mark Hauber produced by Katie Geleff. 

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