When a peacock catches the attention of a female, he doesn’t just turn her head—he makes it vibrate. That’s the surprising conclusion of a new study, which finds that a male peafowl’s tail feathers create low-frequency sounds that cause feathers on the females’ heads to quiver.
The finding is “fascinating,” says Richard Prum, an evolutionary ornithologist at Yale University who was not involved with the work. As far as he knows, it’s the first demonstration that feathers respond to acoustic communication signals from other birds.
Scientists have long known that a bird’s feathers can sense vibrations. Much like a rodent’s whiskers, they are coupled to vibration-sensitive nerve cells, allowing them to sense their surroundings. Feathers can, for example, detect changes in airflow during flight, and some seabirds even use feathers on their heads to feel their way through dark, underground crevices.
When peacocks are ready to mate, they fan out their iridescent tail feathers (known as trains), before rushing at females, shaking those feathers to catch their attention.
But when researchers discovered low-frequency sounds—which are inaudible to humans—coming from this “train rattle” several years back, no one knew how they worked. All they knew was that peahens perked up and paid attention to recordings of these “infrasounds,” even though they couldn’t see the males.
To find out what was going on, Suzanne Kane, a biological physicist at Haverford College in Pennsylvania, and her colleagues decided to look at the feathered crest on top of the peafowls’ heads. During her previous research, she was struck by the resemblance between the short crest feathers—which form a sort of minifan—and the large peacock tail feathers.
Kane and her colleagues gathered the intact head crests of 15 Indian peafowls (Pavo cristatus) and played recordings of the low-frequency sounds produced by the train rattle displays, along with white noise. Using high-speed cameras, they found that the train rattling infrasounds caused the head crests of both males and females to vibrate at their resonance frequency—the point at which they vibrate the strongest—whereas other sounds resulted in little to no movement.
Peacocks also perform a wing-shaking display that Kane says isn’t particularly visually impressive—at least to humans—as it doesn't involve the beautiful tail feathers. However, when the researchers used a mechanical arm to flap a peacock wing in a similar way near three head crests from female peafowl, they found that it caused measurable movements.
“Every time there was a flap the crest vibrated,” Kane explains. This suggests the air flow generated by wing shaking could vibrate the feathers of nearby females, perhaps attracting their attention, the researchers report today in PLOS ONE.
The team cautions that even with the new results, it still hasn’t looked at how female birds respond to these vibrations. Angela Freeman, a biologist at Cornell University who first discovered the low-frequency sounds, says her experiments showed recordings of these infrasounds cause both males and females to become alert and start walking and running, “presumably to locate the signal.”
What scientists need to do next, she says, is figure out how the vibrations are coordinated with other parts of the mating display—and whether the sounds from the shaking tail feathers really do attract the females.