Peacocks are known for being flashy. The male peafowl’s bright feathers are a prime example of biological ornamentation, designed specifically to attract the attention of relatively plain females. Now, scientists have discovered that the peacock’s courtship display involves some complicated physics. In a new study in PLOS ONE, peacock researchers found that during what’s called a "train-rattling" display, peacocks vibrate their feathers in such a way as to make those signature eyespots look as though they’re hovering in front of the moving feathers.
Led by zoologist Roslyn Dakin of the University of British Columbia, the research team took high-speed video of train-rattling during peafowl courtship. They studied a total of 14 adult males—from a group of feral peafowl in California—in the midst of shaking their tail feathers (even if females may not always be looking at them). They also looked at peacock feathers in the lab to test how they vibrated.
They found that the eyespots on peacocks’ feathers barely moved during train-rattling displays—less than 2 millimeters in either direction no matter how hard the peacocks were shaking their stuff. However, the loose feathers around the eyespots moved a lot, a maximum of 9.6 millimeters. From a peahen’s perspective, the eyespots would look stationary while the rest of the peacock’s train would be oscillating around them, the researchers write.
Examining peacock feathers in the lab, they discovered that this was an effect of resonance; if the feathers were shaken at a different speed, the eyespots moved plenty. In other words, the peacocks vibrate their trains at a specific frequency to achieve this visual affect. But the physical properties of the eyespot sections of a feather make it possible. Eyespot barbs lock together with tiny hooks much like those found on feathers designed for flight, while the other barbs remain loose and free to move.
Vibrating a long train of feathers at high speeds takes a lot of muscle power, so being able to create these visual displays may serve as a testament to a male’s physical prowess. Plus there's nothing sexier than prolonged eye(spot) contact.>