“We know, of course, that birds use a variety of materials to line their nests,” Hauber said. “But why are these birds risking their lives to approach these mammals?”
The behavior suggests that the benefit of lining its nest with hair outweighs the danger to the bird, he said.
It may be that the birds simply need the hair to insulate their nests, but the presence of mammal hair – and the associated odor of the mammal – could also deter nest predators like snakes or other birds, the researchers said.
“There’s a local species called the great crested flycatcher, which, like the titmouse, is a cavity nester, that actually puts shed snakeskins into its nest, possibly to deter predators,” Brawn said.
“There are finches in Africa that put mammalian fecal material on top of their enclosed nests, presumably to confuse and thus keep predators away,” Hauber said.
The hair also may repel nest and nestling parasites, which are a common threat to chick survival, especially in cavity nests like those of titmice, he said.
Regardless of the purpose of the behavior, the new paper is the first to document so many examples of hair-plucking by birds in a single report. In addition to citing nine papers about the phenomenon, it also links to dozens of online videos. Collectively, the videos show titmice – and in one case, a black-capped chickadee – plucking hair from 47 humans, 45 dogs, three cats, three raccoons and a porcupine.
“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,” Pollock said.