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How Do Hummingbirds Hover?


Story at-a-glance -

  • Researchers at the University of Berkeley’s Animal Flight Laboratory studied hummingbirds to determine what type of airflow conditions caused them to work at maximum capacity to remain hovering in place.
  • The birds were put into a combination wind tunnel and bird feeder, and were exposed to three different wind speeds and three different-sized vortices created by three different-sized cylinders.
  • What the researchers learned was that it’s not wind speed that causes hummingbirds to rev up their metabolism, but the size of the vortex they must adjust to. When the air’s vortices are wider than their wings, the birds have to work harder to hover.
  • Scientists often turn to nature to help explain and understand glitches in their research. Studying the amazing innate abilities of animals often advances human knowledge. The result of this study may one day enhance flight technology, making planes more resilient and energy-efficient in turbulent conditions.

By Dr. Becker

If you’ve ever been on a bumpy flight while traveling by air, you know how jarring it can be to your entire system, even when you’re sitting inside the (relative) comfort of a commercial airplane. Yet every day, birds fly in turbulent air. Have you ever wondered how they make it look so easy?

Until recently, it was unknown what impact these pockets of turbulence have on a bird’s energy expenditure and ability to control movements in flight. But to shed a bit of light on the subject, a team of researchers at the University of Berkeley’s Animal Flight Laboratory has now provided new insight into the hovering skills of hummingbirds. The researchers evaluated which conditions cause the birds to max out their extraordinary metabolism levels.

In their study published in March in the Proceedings of the Royal Society B,1 the UC Berkeley researchers revealed at what levels of intensity air turbulence causes hummingbirds to expend the greatest amounts of energy.

Hummingbirds Have Spectacular Hovering Skills

All birds, including hummingbirds, can hover for extended periods thanks to the balance of the up and down movements of their wings. A bird’s wings move horizontally, going across, rotating, and then coming back up as the bird moves.

According to researcher Robert Dudley, a UC Berkeley integrative biology professor who also heads the Animal Flight Laboratory, hummingbirds in particular are “super-specialized” when it comes to their hovering skills. And Dudley should know – he’s been studying them for 15 years.

In their experiment, which involved five Anna’s hummingbirds, the researchers placed the birds inside a wind tunnel/bird feeder with an artificial flower attached at one end so they would hover in place. While they fed, the researchers turned on the wind in the tunnel, and the birds had to adjust to the changes in airflow and turbulence.

The hummingbirds were exposed to three different wind speeds (three, four, and nine meters per second), and three different-sized vortices created by differently sized cylinders (two, four, and nine centimeters in diameter). The researchers measured the birds’ oxygen consumption and metabolism in each scenario.

The Wider the Vortex, the Harder Hummingbirds Must Work to Hover

Dudley and his colleagues learned it was not wind speed that boosted the birds’ metabolism, but the size of the vortex created by the cylinders. When the birds flew in the two- and four-centimeter cylinders, they expended only normal levels of energy. But when they flew with the vortex created by the nine-centimeter cylinder, which was similar in size to the wingspan of a hummingbird, the birds showed a 25 percent increase in metabolism.

According to the research team, if science can understand how hummingbirds use their tails and wings to exercise stability and control under different amounts of turbulence, manufacturers of micro air vehicles (MAVs) might someday be able to mimic those mechanisms in MAVs to make them more resilient and energy-efficient under turbulent conditions.

Next, the UC Berkeley team plans to evaluate the metabolism of hummingbirds in naturally occurring turbulent conditions.

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