Micro-drones, tiny aerial vehicles, mainly used for surveillance, are now able to fly nearly as efficiently as hummingbirds.

Hummingbirds were compared to the tiny drones in a study aimed at determining the capabilities of the most modern mini-spy craft.

An international team of researchers examined several species of hummingbirds, finding those animals exhibited about 20 percent greater efficiency than today's best mini-drones. However, the artificial craft were nearly as efficient at flying as most of the birds.

"Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost," researchers wrote in an article announcing their study.

Researchers from Stanford University, the Eindhoven University of Technology, the University of British Columbia, and Wageningen University in the Netherlands all took part in this study.

They carefully studied hummingbird wings from museum collections, trying to understand how efficiency compared to drag in the structures. The tiny wings were connected to a wing spinner, allowing researchers to measure the frequency and power needed for the tiny animals to hover. The amount of power needed for a hummingbird to stay aloft is fairly small; meaning the drag created by its wings had never before been accurately measured. Video recordings were also taken of hummingbirds in flight, to better understand their motion, as the wings flap up to 80 times each second.

This provided researchers with a way of understanding how upward lift is created by the wings, and how this compares to artificial structures. The Black Hornet, a tiny surveillance drone weighing just over half an ounce, was the mini-drone used as a subject in the research.

Anna's hummingbird was found to be the most efficient flier - eclipsing other species of the bird, as well as the miniature drone.

"This shows that if we design the wings well, we can build drones that hover as efficiently, if not more efficiently, as hummingbirds. But if we focus on aerodynamic efficiency, we are closer than we perhaps ever imagined possible," David Lentink, assistant professor of mechanical engineering at Stanford University, said.

Hummingbirds still have some flight advantages over mechanical drones. The tiny birds are better able to withstand wind gusts than the Black Hornet. They are also more adept at finding their way through a crowded field of objects, searching for a target.

"Studying hummingbird wing shapes can not only give insights into the biomechanics of animals, but the gained insights can also be used to build the next generation of flying micro robots," Mirko Kovac of the Imperial College London said.

Investigation of micro-drones and how their flight capabilities compare to hummingbirds was profiled in the journal Interface, published by The Royal Society.

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