The study revealed the mechanisms behind the effortless way that hummingbirds fly backwards.
Although hummingbirds routinely fly backwards, it has never before been scientifically described in detail, the 'BBC News' reported.
University of California scientists Dr Nir Sapir and Robert Dudley, recorded the birds' flight biomechanics using high-speed cameras and oxygen uptake.
Backward flight is frequently used by members of the hummingbird family as they reverse from a nectar-bearing flower after feeding.
Sapir noticed this while observing hummingbirds on a feeder.
"I actually saw it happening in a feeder that was positioned in my balcony. Many hummingbirds were using it and they all were flying backwards. It puzzled me that we know almost nothing about this flight style," Sapir said.
Scientists looked at hummingbirds' oxygen uptake, body posture and wing stroke plane as they flew forwards, backwards or hovered.
The most important finding, according to Sapir, was that flying backwards uses a similar amount of energy to flying forwards, both of which were more efficient than hovering.
Hummingbirds in backwards flight had a more upright posture than when flying forwards.
This was discovered by using a respiratory mask to measure the rate of oxygen consumption during feeding.
"The findings were very exciting because we expected that backward flight will come with a greater metabolic cost," explained Sapir.
The results are published in the Journal of Experimental Biology.
