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Re: hovering diversity (was Re: Ornithurine diversity)

For my observations, I've got to go with the updraft explanation.
Unless by "long time":

I do as well - in the cases of kiting by bluffs or cliffs, as you described, the animals are almost certainly using deflected flows.

] you simply won't notice the sink rate unless you watch one for a
] long time

you mean something on the order of minutes, hours, or days...

Minutes, in that case. Again, though, it only applies to cases where there is no orographic lift involved. My point was to demonstrate what happens in the most simple situation, and why even that case can give the appearance of zero sink. An actual zero sink situation obviously requires a lifting condition.

In what I've seen it appears the birds don't so much appreciate the
gusts.  It is, of course, gusty around here (I've had cause to worry
about getting blown off the bluffs...), but when it gusts is when you
do see the birds move.

It depends on the situation, naturally. If they're staying steady in a deflected flow, then a strong gust might be disadvantageous. However, gusts also represent a source of energy that can be utilized to stay aloft or reposition for low cost.



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