Some tiny birds take bold risks to gather a beakful of hair for their nests. Titmice have been spotted dive-bombing cats, alighting on dozing predators’ backs and plucking strands of hair from people’s heads. Now, there’s a term for the unusual behavior: kleptotrichy.

Derived from the Greek words for “to steal” and “hair,” kleptotrichy has rarely been described by scientists, but dozens of YouTube videos capture the behavior, researchers report online July 27 in Ecology. Titmice — and one chickadee — have been caught on video tugging hair from dogs, cats, humans, raccoons and even a porcupine.

“Citizen scientists, bird watchers and people with dogs knew this behavior much more than the scientists themselves,” says animal behaviorist Mark Hauber of the University of Illinois at Urbana-Champaign. “Popular observations precede science rather than the other way around, which is a valid way to do science.”

Scientists counting birds in an Illinois state park in May 2020 spotted a tufted titmouse plucking fur off a dozing, unbothered raccoon. The team dubbed the behavior “kleptotrichy” after a search of the scientific literature and amateur videos on YouTube turned up more than 100 instances of hair thievery by birds.

Witnessing a bird steal hair from a mammal in the wild is what first inspired Hauber’s colleague, ecologist Henry Pollock, to dig deeper. While counting birds in an Illinois state park in May 2020, Pollock and colleagues spotted a tufted titmouse pluck fur from a sleeping raccoon. “I was like, ‘Wow, I’ve never seen anything like that,” says Pollock, also of the University of Illinois at Urbana-Champaign.

In South America, palm swifts snatch feathers from flying pigeons and parrots — a behavior already known as kleptoptily. Searching through the scientific literature, Hauber, Pollock and colleagues found only 11 anecdotes of birds stealing hair from live mammals. While most published accounts involve titmice in North America, at least five other bird species get in on the action. Researchers have seen an American crow harvest hair from a cow and a red-winged starling in Africa peck a small antelope called a klipspringer. In Australia, three honeyeater bird species steal fur from koalas.

Meanwhile, a YouTube search by the team turned up 99 videos of tufted titmice, a mountain chickadee and a black-crested titmouse plucking hair from mammals. The latter two bird species had not previously been identified as hair thieves in the scientific literature.

Scientists generally assume that birds gather hair for their nests in low-risk ways, relying on carcasses or stray fluff shed into the wind. “Plucking hairs from raccoons, which are common avian nest predators, suggests that it’s obviously worth it to get that hair,” Pollock says.

Hair-harvesting species tend to live in colder climates, so those birds probably prize hair’s insulating properties, the team says. Some birds might also spruce up their nests with mammal hair to confuse would-be predators and parasites (SN: 8/28/01).

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