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Re: hovering diversity (was Re: Ornithurine diversity)



I fear that either your misunderstanding Dann or the birds know
something you don't.  The phenomenon is called "kiting", and I see it
all the time on the bluffs above the beaches near Santa Barbara.  The
first time I saw it I was blown away because the bird really looks
like a kite on a string...  absolutely motionless.

I am also quite familiar with kiting, and Jim is correct: a simple headwind will not allow the animal to maintain a constant altitude. In a constant headwind, the bird is actually gliding - by matching glide speed to the wind, it can have a ground-speed of zero, but it will still sink over time, just like any glide. Thus, it's not a true hovering dynamic.


Of course, the conditions used for kiting are often not a constant wind, but can contain gusts - which contain energy that can be used to help keep the animal aloft. Even in the most simple form of kiting (gliding into a steady, oncoming wind), many birds won't appear to be obviously sinking because they have quite good glide ratios. Gannets, for example, use the technique regularly to loiter over fish schools (to line up a plunge dive). With an aspect ratio of about 14, they have a very good glide ratio - you simply won't notice the sink rate unless you watch one for a long time (and it'll probably adjust or dive before it ever moves downward enough to be perceptible).

Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu