One of the most amazing things about hummingbirds is that they fly backwards — and they do it a lot!

Every time they feed, which is about once every two minutes, they reverse when they leave the flower.  You’ve seen them do it.  They raise their heads, seem to stand up straight, and glide backwards.

Dr. Nir Sapir wondered,  Does this posture create more drag than forward flight?  Is it harder to do than hovering?

So he and his postdoc advisor Robert Dudley used high speed cameras to observe five Anna’s hummingbirds in a wind tunnel at University of California, Berkeley.  They changed the position of the nectar source and varied the wind speed from 0 to 3 meters per second (6.7 mph) so the birds had to fly forward, hover, or fly backward while feeding.  They also used an ingenious shroud around the feeder to measure the birds’ oxygen consumption and gauge their exertion.

The results were somewhat surprising.  For a hummingbird, backward flight is just as efficient as forward and 20% more efficient than hovering.  Drag isn’t a problem because hummingbirds fly backward rather slowly.  In the wind tunnel they gave up on backward flight when the wind reached 4.5 meter per second (10 mph).

So if you ask a hummingbird about flying backward, it’s easy!

Click here for more information on this study at BBC Science News.

(photo by Marcy Cunkelman)