Hummingbird Flight Both Adaptable And Efficient
September 27, 2012

Study Shows Hummingbird Flight Is Both Adaptable And Efficient

Brett Smith for - Your Universe Online

Hummingbirds are among the most impressive aviators in the animal kingdom. Beating their wings at a rate of up to 80 times per second, they can fly forward, backward, left and right with the greatest of ease.

After noticing the birds flying around a feeder on his balcony, University of California at Berkeley biologist Nir Sapir decided to investigate the mechanics of this acrobatic aviator and was surprised to find that the there was very little scientific literature on the subject. While significant research has been done on hummingbird migration and mating habits, for instance, few studies have focused exclusively on the mechanics of their flight.

“This was a bit surprising given that they are doing this all the time,” Sapir said. “I thought that this was an interesting topic to learn how they are doing it and what the consequences are for their metabolism.”

Along with his colleague Robert Dudley, Sapir analyzed the birds´ flight abilities and metabolism and published his findings in the latest edition of The Journal of Experimental Biology.

To accurately measure the birds´ metabolism during flight, the researchers used a technique called mask respirometry that involves a feeding apparatus equipped with a device that records a bird´s respiration.

Sapir and Dudley also used a wind tunnel and video camera to measure the hummingbirds´ flight techniques as they extracted a liquid sucrose solution from a syringe disguised as a flower.

First, the researchers filmed each bird as it hovered at the feeder and left after it was sated. Next, Sapir activated the wind tunnel and set up the feeding apparatus so that a 3-meter-per-second airflow pushed the bird, forcing it to fly backwards against the wind in order to remain at the feeder. Finally, Sapir repeated the experiment but this time rotated the feeder 180 degrees so that the hummingbird had to fly forward into the wind to continue eating.

The team then analyzed the video replay of all three flight styles. They found that the hummingbirds' shifted to a more upright posture as they flew backward. This position forced them to bend their heads more so that they could insert their beaks into the faux flower, the researchers noted.

They also found that birds flying in reverse altered the angle and frequency of their wing beat to maintain this posture. They noted that the wings beat in a more horizontal direction and at a greater frequency, 43.8 Hz instead of the 39.7 Hz that they use while flying forward.

“That is quite a lot for hummingbirds because they hardly change their wing beat frequency,” Sapir said.

The team also used the mask respirometer to determine the birds´ metabolism during all three forms of flight.

“We expected that we would find high or intermediate values for metabolism during backward flight because the bird has an upright body position and this means that they have a higher drag,” he said. “Also, the birds use backward flight frequently, but not all the time, so we assumed that it would not be more efficient in terms of the flight mechanics compared with forward flight.”

However, Sapir and Dudley found that backward flight used just as much energy as forward flight and both were found to be about 20 percent more efficient than simply hovering.

Sapir said that his future studies would focus on other animals that can perform similar aerial acrobatics, such as small songbirds and nectar-feeding bats who can reverse, too.