UC Berkeley researchers observe hummingbirds in turbulent environments

Victor Ortega/Courtesy

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Researchers in UC Berkeley’s Animal Flight Laboratory have provided key insight into the hovering abilities of hummingbirds, discovering which conditions provoke hummingbirds to reach their exceptional metabolism levels.

The study — published last month and co-authored by UC Berkeley postdoctoral researchers Victor M. Ortega-Jimenez, Nir Sapir and Marta Wolf, as well as UC Berkeley integrative biology professor Robert Dudley — revealed what levels of turbulence cause a hummingbird to expel more energy. Their findings could one day be used to enhance the performance of micro air vehicles.

Hummingbirds, unlike all other birds, have the ability to hover for extended periods due to the symmetry of the downstroke and the upstroke of their wings. The wings are moving on a horizontal plane, going across, rotating and then coming back up while the bird moves.

“They have a whole variety of morphological and physiological adaptations that let them do that — they’re very super-specialized,” said Dudley, who leads the Animal Flight Laboratory. “They are an amazing group to study flight control and maneuverability — that’s part of the reason why we’ve been working with them for 15 years.”

In the experiment, five “Anna’s hummingbirds” were perched inside a wind tunnel with an artificial flower affixed to one end so the bird would hover in place. While the bird is feeding, the wind is turned on, and the birds must adjust to the conditions.

While inside the tunnels, the hummingbirds were exposed to different wind speeds — three, four, and nine meters per second — and three differently sized vortices created by differently sized cylinders. Their oxygen consumption, and thus metabolism, was measured with a mask inside the feeder.

Researchers found it was not wind speed that increased their metabolism but the size of the vortex. When flying in vortices created by cylinders two and four centimeters in diameter, the hummingbirds did not expend any more energy than usual. It was not until they flew with a vortex created by a nine-centimeter cylinder — similar to the wingspan of a hummingbird — did the hummingbirds experience a 25 percent rise in metabolism.

By understanding how hummingbirds use their tails and winds for stability and control under different levels of turbulence, engineers who manufacture micro aerial vehicles could one day emulate this mechanism in these devices and potentially make them more resilient in turbulent conditions.

“While micro aerial robots can fly in very quiet conditions, the problem is that they cannot in turbulent conditions,” Ortega said. “Then this study can help engineers to make more controllable and stable these flying devices.”

According to Ortega, the next step is to measure the metabolism of animal fliers in turbulent environments in nature to see if this study also happens when hummingbirds travel in natural turbulent conditions.

Contact Chris Tril at [email protected] and follow him on Twitter @ctril.