may be considered rats of the sky, but some scientists have found greater value
in these urban birds: the blueprint for a new generation of flying machines.

can modify the shape of their wings by fanning out their feathers or shuffling
them closer together. Those adjustments allow birds to cut through the sky more
nimbly than rigid drones. Now, using new insights into exactly how pigeons’
joints control the spread of their wing feathers, researchers have built a robotic pigeon, dubbed PigeonBot,
whose feathered wings change shape

like the real deal.

This research
paves the way for creating more agile aircraft, says Dario Floreano, a
roboticist at the École Polytechnique Fédérale de Lausanne in Switzerland not
involved in the work.

birdlike wings, airborne machines could make tighter turns in
cluttered spaces, such as around buildings or in forests, and could better
navigate rough air, Floreano says (SN: 1/24/15). The new robot,
described January 16 in Science Robotics, also offers a way to study the
nuts and bolts of bird flight without animal experiments.

bent and extended the wings of dead pigeons to investigate how the birds
control their wing shape. Those experiments revealed that the angles of two wing
joints, the wrist and the finger, most affect the alignment of a wing’s flight
feathers. The orientations of those long, stiff feathers, which support the
bird in flight, help determine the wing’s shape. Based on those findings, the
team built a robot with real pigeon feathers, whose faux wrists and fingers can
morph its wing shape as seen in the pigeon cadavers.

Besides laying
the groundwork for building more graceful drones, “what’s really cool about
this robot is … you can make manipulations in a robot wing that you could never
do or want to do in a bird” to study flight, says David Lentink, an engineer
and biologist at Stanford University.

instance, Lentink wondered whether a pigeon could steer itself just by bending the
finger joint of either its left or right wing. “The problem is, of course, I
don’t really know how to train a bird to just move its finger — and I actually
am very good in bird training,” he says by phone, as two pet birds chirp in the

A controllable
robotic pigeon solves that problem. In flight tests, Lentink’s team observed
that bending only the finger of one wing eased the robot into a banked turn —
offering the first evidence that birds may sometimes use just their fingers to steer
in flight.

PigeonBot wing
With two bendable joints, wrist and finger, the wings of a new robotic pigeon can bend into different shapes (three options overlaid on each other, above).Lentink Lab/Stanford Univ.

In a
second study, reported in the Jan. 17 Science, Lentink’s group used
their robotic wing design to confirm another insight into bird flight: how gaps
are prevented from forming between feathers on extended wings. In experiments
that involved rubbing one bird feather across the top of another — to mimic
overlapping flight feathers fanning out — researchers found that two feathers
initially slid apart easily, but then snagged on each other. Scanning electron
and X-ray microscopy images revealed that tiny hooks protruding from the top
of one feather latch onto ridges

on the underside of the other when they slide too far apart. Those microscopic hooks
unfasten when the feathers slot back together.

the secret. They have this directional Velcro” that holds feathers together,
Lentink says.

A robotic pigeon that can change its wing shape like a real bird paves the way for creating more agile aircraft, and offers a new way to study bird flight.

confirm the effect of these microstructures, the researchers rotated the
feathers on their robot so that they wouldn’t slide against each other when wings
were extended. In wind tunnel and outdoor flight tests, gaps formed between
feathers on the modified robot wings, undermining the wings’ stability. 

This is the best set of robotic wings yet for testing how birds coordinate their flight feathers to maneuver through the air, says Tyson Hedrick, a biomechanist the University of North Carolina at Chapel Hill not involved in the work. But “there’s plenty of room for improvement.” For instance, a future flying robot could include a shoulder joint, to investigate how tilting a bird’s wings up and down influences flight, he says.