The beautiful display peacocks make when trying to attract females is much more than a beautiful, colorful show. The movement and sound they produce when showing off their amazing feathers are key components of the complex ritual to find mates, according to a paper published Wednesday in the journal PLOS One. A biologist and a physicist joined forces to study the full picture of the physics behind train rattling.
While Dr. Roslyn Dakin, a biologist, had been looking at the color of peacock feathers, physicist Suzanne Amador Kane had been studying visual signals by animals. Dr. Dakin wanted to know more about the way peahens perceive the eye-spots and Dr. Kane was interested in the relation between the motion of the feathers and the visual abilities of females.
They knew that the motions by peacocks’ feathers were a key part of courtship, so they videotaped the males during their natural ritual behavior and found that they display their feathers very often during courtship season, but they don’t make them vibrate when peahens are not around.
Alongside several colleagues, Dr. Dakin and Dr. Kane also found that the iridescent eyes stay still while the rest of the tail is shaking, giving an image of eyes spots floating over a moving background. Males use their tail feathers to strum the train feathers like a guitar and create vibrations at resonance.
Dr. Dakin, who is a researcher at the University of British Columbia, said in an email to Christian Science Monitor that a peacock’s huge fan of feathers has the potential to completely cover a peahen’s field of view. When he starts shaking his feathers the female can see everything in motion, except for the green-blue eyespots floating.
Peacocks shake their feathers at a perfectly synchronized rhythm
High-speed video footage of males during mating season showed this train-rattling display. After capturing this material, the researchers took individual feathers to the laboratory and shook them at different frequencies to determine their natural frequency. They then determined the peacocks strum them at resonance, which means that the vibration that keeps the tail feathers shaking occurs at a frequency very close to the feather’s natural frequency.
Dr. Kane, an applied physicist at Haverford College, explained the phenomenon by comparing it to pushing a child on a swing.
“If you just pull them back and let them go, they swing at a pre-set frequency. The rate at which they swing back and forth is set by the mechanical properties of the swing and not how you’re pushing them,” she told Christian Science Monitor by phone. “So if you want to push them effectively and not waste your energy, you give them one push every time they swing back toward you.”
Dr. Kane said resonance is what happens when someone is pushing a child on a swing in sync with the natural frequency. The same occurs with peacocks, who strum their tail feathers at the right rhythm to match the natural frequency of their train feathers. This natural frequency is determined by those feathers’ properties.
The resonance creates a mechanical sound and suggests the peacocks make the display in a way that is energetically efficient.
In addition, the paper reveals that peacocks with longer, heavier feathers shake them faster instead of doing it slowly as researchers had expected.
The research team intends to use these findings to conduct further research in order to find out how peahens perceive all this effort and the impact it has on them. The first step was to better understand the physics behind the display and researchers are now able to study what exactly drives success in the courtship behavior.
Source: Journal PLOS One