Birds have been caught stealing fur from live mammals many times, and victims vary from squirrels to predators and even humans.

Although it can seem entertaining to watch a chirpy bird try to snatch body hair from animals, scientists revealed this mischief is no simple task.

Nests of the tufted titmice (Baeolophus bicolor), and their closest relatives, are often full of fur from mammalian carnivores.

Scientists previously thought the fur was collected from carcasses or an animal shed. However, it is more likely to have come from live animals. Titmice use the soft material to construct a safe, warm, and comfortable nest for their offspring. For these loving parents, it is no big deal to go the extra mile for quality materials.

“There is a lot of evidence of birds using hair in their nests,” University of Illinois postdoctoral ornithology researcher Henry Pollock said according to LiveScience. “Where that hair is sourced from has never really been investigated.”

However, it is becoming evident these little birds regularly sneak it off from the back of living animals, including predators that might consider the winged creatures to be a tasty treat.

A research paper from A. C. Bent dating back to 1946 shows he once saw a titmouse pluck hair from a red squirrel’s tail. The paper did not mention it was common behavior across the species.

While the scientific world did not pay much attention back then, Pollock and his colleagues have found ample online recordings of similar behavior uploaded by bird watchers. Many cases revealed titmice steal fur not only from domestic pets but even porcupines. 

Science Alert revealed the behavior is rather widespread, and not confined to titmice.

The birds also collect animal hair while scavenging. This raises the argument that even titmice prefer to avoid the risks of stealing fur from live predators.

“There is a clear fitness benefit to the behavior, or it would not have evolved,” Pollock said.

He speculates live animal fur helps the birds resist predators or parasites that could pose various dangers to tiny hatchlings.

Pollock’s research team found stealing is common behavior in higher latitudes. This could help explain why birds need fur to keep themselves warm.

“Unexpected interactions such as these remind us that animals exhibit all types of interesting and often overlooked behaviors, and highlight the importance of careful natural history observations to shed light on the intricacies of ecological communities,” he said according to Science Alert.

Researchers coin the behavior “kleptotrichy,” a Greek-derived expression meaning “stolen hair.”