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Re: hovering diversity (was Re: Ornithurine diversity)

The first of the quotes below, "Yes, I've always......", wasn't me. Don't know who said that.

Other comment(s) inserted below

----- Original Message ----- From: "Mickey Rowe;893-2446" <mrowe@lifesci.ucsb.edu>
To: <dinosaur@usc.edu>
Sent: Wednesday, July 16, 2008 9:28 AM
Subject: Re: hovering diversity (was Re: Ornithurine diversity)

Jim Cunningham (jrccea@bellsouth.net) instructs:

Yes, I've always thought it ironic that that's by far the most
common mechanism by which actual kites hover.

The statement above isn't from me (JimC)

They will usually only resort to the flutter stroke when no external
energy source is available, because it takes a very high power input

While I'll accept that there has been selection to make your statement true when averaged across birds, within species your reasoning doesn't really match the facts.

Actually, it does. See below.

As I mentioned before, I've only once seen a
kite kite, but most of the times I've seen a kite in the air it's been
using a flutter stroke.

This means that when you saw them using the flutter stroke, there was not a sufficient source of atmospheric lift available. Had there been an atmospheric lift source present and sufficient for hovering, and had they also been using the flutter stroke, they would have been rising rather than hovering. That said, if lift is present and the windspeed is less than minimum glidespeed, they can also modulate the flutter stroke with available atmospheric lift in order to adjust airspeed to give them zero groundspeed (hover). If the windspeed is faster than minimum glidespeed, they are forced to glide rather than flutter in order to hover.

American kestrels also typically hunt using that stroke.

Same as above. When sufficient lift is available, they don't need the flutter stroke for hovering, and it wouldn't be appropriate to use it (except to adjust for slow winds) since it would cause the bird to rise. Most birds that use the flutter stoke for hovering spend a lot of time hovering in insufficient atmospheric lift (which is why they use the flutter stroke).

Both animals typically hover over flat grassy areas.

A condition where there is often no significant atmospheric lift available close to the ground.

I have seen red-tailed hawks flutter, but they're the opposite of kites;

That went over my head. In what way are they opposites (this is actually more a question involving the jargon meaning of the term 'opposites') ?

I see red-tails a lot more frequently but have seen one flutter only
once or twice.

I see them flutter fairly often, but there are a lot of them around here, and its so flat that we give names to the highest cotton rows (our equivilent of mountains :-)

Erik Boehm (erikboehm07@yahoo.com) opines:

] Given the size of most bluffs/ coastal cliffs, and a birds excellent
] vision.  I doubt they'd go anywhere but the easiest place to
] /hoversoar while scanning for food/hunting - since we aren't talking
] a huge distance, or much change in what they can see/perspective.

But a) you seem to be completely ignoring the fact that not only do
the birds need to see their prey but they also need to ensure their
prey don't see them in time to get away, and b) the bluffs I'm talking
about are adjacent to a fairly flat area with almost no trees for
about 2 km along the bluff and about 200 meters perpendicular to the
bluff edge.  The birds' vision is acute enough that they could see a
rabbit at the far edge of the clear space, but when they're kiting,
they're always looking down (except when they're looking at other
nearby kiting birds).  I'm thinking they want to be high enough not to
be seen easily by the things they're hunting, and their strategy is to
find something they can drop straight down on to maximize their speed
of attack.

I agree with Mickey on this (and yeah, Mickey -- I know your general objection to statements of agreement..... :-)

All the best to all,