I found this short article on the Scientific American magazine website
and I thought it was worth sharing. This article is freely available to all
who access the site...
http://www.sciam.com/article.cfm?chanID=sa003&articleID=0002A840-B9B9-12B9-B9B983414B7F0000
Jim Wilson
Queenstown,MD
High-Tech Pictures Reveal How Hummingbirds Hover
Hummingbirds are famous for their hovering ability, which lets them
linger in front of flowers and feast on their nectar. But just how the
creatures manage to stay aloft has intrigued researchers for years. New
findings published this week in the journal Nature indicate that when it
comes to flying, a hummingbird's style is halfway between that of a bird and
an insect.
Previous investigations into the flight of the hummingbird had
suggested that it could be employing the same mechanisms as insects, which
often hover and dart in a manner similar to the bird. "But a hummingbird is
a bird, with the physical structure of a bird and all of the related
capabilities and limitations," explains Douglas Warrick of Oregon State
University. "It is not an insect and it does not fly exactly like an
insect." To unravel the hummingbird's aerial secrets, Warrick and his
colleagues used a technique called digital particle imaging velocimitry
(DPIV). Usually employed by engineers, DPIV uses microscopic particles of
olive oil that are light enough to be moved to and fro by the slightest
changes in air currents. As a pulsing laser illuminates the droplets for
short periods of time, a camera captures them on film. From the resulting
images, the scientists determined exactly how the bird's wings move the air
around them.
The results indicate that hummingbirds get 25 percent of their lift
capacity from the upstroke beating of their wings; the other 75 percent of
the lift comes from each downstroke. Insects, in contrast, divide the work
equally, getting 50 percent of the lift from each, and other types of birds
rely solely on the downstrokes. "What the hummingbird has done is take the
body and most of the limitations of the bird," Warrick says, "but tweaked it
a little and used some of the aerodynamic tricks of an insect to gain
hovering ability." --Sarah Graham |