The mystery of how birds fly, morphing their wings into a variety of shapes that allow unparalleled feats of soaring and diving, has finally been solved by scientists.
Feathers contain a ‘natural Velcro’ of tiny hooked hairs which lock together as the bird opens its wings, creating a fixed, sturdy shape, rather than simply overlapping, researchers have found.
The discovery by Stanford University, was described as ‘pretty cool’ by bird experts, who said they knew that individual feathers contained specialised structures to help maintain their form, but had not realised they could interlock to form fixed wings.
Just like Velcro used in fasternings, it is even possible to hear the distinctive ‘ripping’ sound as feathers are pulled apart again and folded back in the bird’s body, scientists discovered.
In fact, the only birds who do not have the feather-fastening system are night-hunting predators like owls, who need to catch prey unawares in the silence of the dark, and appear to have made an evolutionary trade-off, swapping greater maneuverability for stealth.
The researchers say the findings could inspire new kinds of morphing aircraft.
Writing in the journal ‘Science’, Laura Matloff, of the Department of Mechanical Engineering at Stanford, said: “Variable feather overlap allows birds to morph their wings, unlike aircraft.
“Distinctive microstructures form ‘directional Velcro’ such that when adjacent feathers slide apart during extension, thousands of lobate cilia (small lobed hairs) on the underlapping feathers lock with hooked rami of overlapping feathers to prevent gaps.
“These structures automatically unlock during flexion (when the bird draws its wings in).
“We found that the hooked microstructures fasten feathers across bird species except silent fliers whose feathers also lack the Velcro-associated noise.”
The discovery was made after scientists noticed that when they slid two pigeon feathers together they glided across each other naturally, before suddenly stopping, and becoming fixed together.
They then looked at the feathers underneath scanning electron and x-ray microscopes and found hooked and looped hairs called cilia and rami that act like Velcro.
Previously it had been suggested that feathers were sucked together by the friction of rubbing against each other, but the scientists showed that they did not create enough force when sliding across each other to give sufficient stick.
A spokesman for the RSPB said experts were aware that individual feathers have mechanisms to maintain form, but nobody had realised that there were mechanisms between feathers that help to maintain wing form.
Paul Stancliffe, of the British Trust for Ornithology added: “We knew that individual feathers worked like this but this is the first time I and my colleagues that I have spoken to about this have heard of this mechanism for the morphing of a wing to create a fixed wing, and then undoing this when the wing flexes.
“This is pretty cool.”
The team also created a robotic bird dubbed ‘PigeonBot’ to find out what would happen to birds without the Velcro system. They found that resulting gaps between the feathers made it much harder to create fixed wing shapes and control the robot.
They also scanned a number of dead pigeons to work out the mechanics of wing extension and discovered that wrist and finger bones beneath the feathers are able to finely control feather placement and wing span.
Replicating the movements in ‘Pigeonbot’ allowed far better control of the mechanical bird, allowing scientists to make sharp turns and banks, which are unachievable with normal robotic aircraft.
It also showed for the first time that birds use their fingers to steer in flight.