mid-air braking to prioritize safety over power or speed

Researchers at the University of Oxford have found that hawks control their flight to ensure the safest landing conditions when landing, even if it takes more time and more energy. Understanding how birds optimize their landing maneuvers through learning could help develop small aircraft capable of landing like birds.

In new research published in Nature, four Harris’s hawks wearing small retroreflective tags were tracked flying back and forth between two perches. Their precise movements were recorded by 20 motion capture cameras located around the room, allowing the research team to reconstruct their trajectories over 1,500 flights. The research team then used computer simulations to understand why the birds chose their particular route to the roost.

Airplanes have the luxury of using a tarp after landing to slow down. In contrast, birds must stop before reaching landing—but slowing down to a safe speed while in flight risks stalling, resulting in a sudden loss of flight control. The researchers found that the hawks follow a flight path that slows them down to a safe speed but minimizes the distance from the landing at which they stop.

To minimize stalling, the hawks dived down while flapping before spreading their wings in a gliding posture as they descended to land. By choosing the right speed and position from which to ascend to the perch, the birds were already within grasping distance of the perch when they stopped, keeping their landing as safe and controlled as possible.

Co-author Dr Lydia France, Department of Biology, University of Oxford, said: “We found that our birds do not optimize either time or energy expenditure, so their flight paths are neither the shortest nor the cheapest options for getting from A to B. Instead, our birds reduced the distance from the landing where they stopped and were even better at limiting the crash than our simplified computer model.’

“The three young birds flew directly between perches by flapping for the first few flights of the familiarization period, but soon adopted the indirect flapping behavior characteristic of experienced birds,” explained one of the lead authors Dr. Marco Klein Heerenbrink, Department of Biology, University of Oxford.

Landing is a critical maneuver and stalling is the cause of many aircraft accidents. Looking at birds and asking how they solve the problem of landing safely can help us find new bio-inspired design solutions for our own technologies, including small aircraft capable of landing like birds.

Understanding how birds learn complex motor tasks such as landing could also help improve artificial intelligence (AI). When aeronautical engineers use computers to solve the landing problem, using a trial-and-error approach to refine the data, finding an answer can take tens of hundreds of hours. Yet the hawks find an optimized solution for several fields, showing the gap that still exists between natural and artificial intelligence.

“Motion capture technology has allowed us to analyze thousands of flights at once, addressing questions we could never have done before. Looking ahead, this opens up the tantalizing possibility of understanding how animals learn complex motor tasks, such as learning to fly, and of revolutionizing how robotic systems can do the same,” said senior author Professor Graham Taylor.