On Wed, Jul 16, 2008 at 08:21:04PM +1000, Tom and Mandy Wilson wrote:
> Interesting in all this thread that no-one has picked up that
> an old English name (originating from SW England) for kestrel is
> "windhover". However, I agree with John Tongue that Nankeen Kestrels
> are equally adept at hovering on a still day as using a strong breeze
> to effect a hover. The bird(s) at Long Reef in Sydney have given me
> ample opportunities to observe both types of hover at close range
Windhovering gets used in papers on bird-flight to distinguish maintaining
stationary ground position by flying into a wind I read some of the
research on flight energetics in Common Kestrels in Europe. These papers
don't include any observations of hovering and as far I can tell assume
Common Kestrels don't and perhaps can't do this. Studies of hummingbirds
estimate 0.2W/g to hover, extrapolated to a 150-200g Nankeen Kestrel that
is 30-40 watts. Common Kestrels are estimated to use about 15 watts
in flapping flight and less than 2 watts when hanging on an updraft so
sustained hovering in still air, if possible, looks energetically very
unattractive and should need major reward. Soocumenting this as common
behaviour would be quite publishable. Some of the Common Kestrel papers
are publically available at the appended URLs.
Andrew
http://elibrary.unm.edu/sora/Auk/v104n04/p0603-p0616.pdf
http://jeb.biologists.org/cgi/reprint/102/1/1.pdf
http://jeb.biologists.org/cgi/reprint/155/1/519
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