[va-richmond-general] Flight of the Hummingbird!

  http://news.yahoo.com/s/ap/20050624/ap_on_sc/hummingbird_flight
   
  Study Examines Flight of Hummingbirds 
  By WILLIAM McCALL, Associated Press Writer Thu Jun 23, 9:43 PM ET 

  PORTLAND, Ore. - Not much bigger than a honey bee, the tiny hummingbird is 
able to hover gently over a flower because it uses some of the same wing motion 
as an insect - but not as much as previously thought, a new study says. 

  The hummingbird neatly splits the difference between birds, which get all 
their lift from the downstroke of their wings, and bugs, which get equal 
amounts of lift from both downstroke and upstroke.
  Researchers used sophisticated technology originally developed for 
engineering design to analyze the movement of air around a hummingbird's wings 
and provide details about its flight that had been limited to mere guesswork 
for decades.

  Hummingbirds get about 75 percent of their lift from the downstroke, with the 
remaining 25 percent provided by the upstroke, according to University of 
Portland and Oregon State University researchers.

  For all other birds, the lift is 100 percent downstroke, while bugs are 
50-50, up and down.

  The study demonstrates a strong example of biological convergence - unrelated 
species evolving similar characteristics in order to exploit their niche, said 
Douglas Warrick, an Oregon State zoology professor who led the research 
published this week in the journal Nature.

  "This is probably the result of how far natural selection can take an avian 
body plan toward looking like an insect and functioning like an insect, in 
terms of flight," Warrick said.

  Warrick and University of Portland biologist Bret Tobalske put bird feeders 
in a specially designed wind tunnel equipped with digital particle imaging 
velocimetry equipment - a laser device that is linked to a computer to measure 
the movement of tiny droplets of olive oil swirling in the air.

  The device allowed researchers to take "snapshots" of hummingbird wing motion 
only 250 microseconds - millionths of a second - apart.

  The results challenged previous assumptions about hummingbird wings providing 
equal lift using two strokes, like insect wings, simply because the bird and 
bugs move their wings in a similar pattern, said Michael Dickinson, a Caltech 
bioengineering researcher who studies both insects and hummingbirds.

  "But it's not surprising they can exploit the same characteristics of the 
physical world," Dickinson said. "This really is an example of convergence."

  Warrick noted that bird wings are different than insect wings, with a bony 
structure that is more like a human arm than an insect wing, along with 
feathers that help form a contoured front edge. Flying insects, in contrast, 
have wings that are almost flat, like paddles, allowing bugs to gain lift with 
two mirror-image halfstrokes as the wing moves back and forth in a figure eight 
pattern.

  "They look so similar and function so similarly, and they're about same 
size," Warrick said of the differing wing structures, "and those similarities 
always led people to believe that hummingbirds must fly like insects. But a 
hummingbird will never be anything but a bird."

  Tobalske said the images showed the hummingbird bobbed a little while 
hovering, moving up and down a little as it switched from upstroke to 
downstroke, partly responsible for the difference in the percentage of power it 
uses on the separate strokes.

  Ross Hawkins, founder of the national Hummingbird Society, said the research 
is an example of science improving basic knowledge about nature. He noted it 
took new research to reverse a decades-long national habit of putting honey in 
hummingbird feeders when it was discovered the honey led to a tongue infection 
that killed the birds.

  "We all operate on the basis of certain assumptions," said Hawkins, a former 
chemist. "And scientists are no different than other people, so it's delightful 
when they come out with an unexpected discovery."

  ___

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