Biologists are improving photographic techniques to study the intricacies of flight. Let’s look at what two research labs have been observing about birds and insects. They share amazing similarities in their flight strategies, despite the vast phylogenetic distance between them. This will give us an opportunity to ask what kind of cause could account for these similarities.

“You don’t just partly fly,” Paul Nelson quips in Flight: the Genius of Birds. “Because flight requires not just having a pair of wings, but having your entire biology coordinated towards that function.” As he speaks, we watch a crow temporarily folding its wings and dropping like a rock. It quickly spreads its wings again and takes control of the air, demonstrating the truth of Nelson’s statement. Insects, being lighter, might drop a little slower, but they can’t just partly fly either. And what astounding flyers they are!

A fruit fly can change its flight direction in less than one hundredth of a second. But how does it do that? A firm understanding of how fruit flies hover has emerged over the past two decades, whereas more recent work focussing on understanding how flight manoeuvres are performed. In a review article, as part of the special theme edition of Philosophical Transactions B, Florian Muijers of Wageningen University and Michael Dickinson of California Institute of Technology, describe how flies manipulate wing movement to control their body motion during active manoeuvres, and how these actions are regulated by sensory feedback.

That’s how an article on Phys.org about “the flight of fruit flies under the microscope” begins. Dickinson has been studying these aerobatic champions for over a decade in his lab at Caltech. His fascination has not waned. How can these tiny insects dart about so fast, land on ceilings, and respond quickly to multiple sensory cues with only 1 millionth the neurons of a human brain? How can all their behaviors, including food searching, reproduction, and predator avoidance be packed into such a small space? Using innovative techniques, such as the Tethered Flight Simulator, Dickinson and his students have only begun to answer these questions. In a TED Talk from 2013, you can see his infectious enthusiasm for flying insects as he compares them to engineered aircraft with sophisticated control systems.

The new study explores similarities between tiny fruit flies and larger insects and birds:

Fruit flies move their wings back and forth rather than up and down. This it is remarkably similar to what has been observed in hummingbirds, honey bees and hawk moths. Whether this pattern is optimal with respect to energetics is not entirely clear; nevertheless, the similarity among species is noteworthy and suggests that a combination of physical and biological constraints restrict the solutions available to hovering animals.

What does it take, for instance, to change direction in a hundredth of a second?

To keep in balance during such manoeuvre, the fly must perform corrective movements to control its body orientation. This mechanism uses input from different sensors: the antennae which can detect bilateral differences in airspeed, the visual system which can detect the optic flow created by the fly’s forward motion, and the halteres which are thought to act as gyroscopes by detecting Coriolis forces resulting from body rotation. This allows a fly to correct itself in less than a hundredth of a second.

Like a helicopter, the fruit fly pitches nose down to accelerate. But like an airplane, it banks to change direction. A video clip in the article shows the wings flapping in slow motion. Notice how stable the body is during flight. When it sees a threat, the fly can respond and dart away in less time than an eye blink. In the TED Talk, Dickinson explores some of the computational requirements for these behaviors, and how they can be met with far fewer neurons than we have. He shows a parasitic fly with 7,000 neurons packed into a body the size of a paramecium — and it can fly!

Birds

A colorful lovebird stars in a video from Stanford University posted on the BBC News Science-Environment section. Scientists spent four years designing and building a complex wind tunnel to study bird flight. In real time, the bird darts through the tunnel in about a second, but well-placed high-speed cameras show what really happens. It’s as beautiful and graceful as a ballet.

The researchers want to “study how birds fly to develop better flying airplanes and robots,” the narrator says. “And they want to understand how can it be that birds fly so effectively. We understand so little about it, although we see it every day and take it for granted.” In future work, they want to watch hummingbirds to learn how, unlike other birds, their unique wingbeats provide lift on both forward and backward strokes, allowing them to hover. The Illustra film animates the shoulder joints unique to hummingbirds that allow the wings to rotate, providing optimal lift in both directions.

Vera Causa

So how do hummingbirds and fruit flies share similar wingbeat designs that allow them to hover, despite being phylogenetically distant? Evolutionists sometimes speak as if the environment itself causes different animals to arrive at the same solution (they call it “convergent evolution”). But that cannot be the vera causa (true cause). Constraints cannot bring something into being to meet the constraints. It takes engineering to design a system able to take advantage of opportunities in spite of constraints. It takes superb engineering to optimize a function within the constraints.

The student learns from the master. If top engineers at Caltech and Stanford study fruit flies and birds for decades and still have more to learn, who is the master? It’s not so much the insect or bird; they do what they were programmed to do. The master is the mind that did the programming: an intelligent mind able to teach our designing minds a thing or two about engineering.

Photo credit: Floris van Breugel, Dickinson Lab, via Phys.org.