[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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.
>
> 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.  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.  American kestrels also typically hunt using
that stroke.  Both animals typically hover over flat grassy areas.  I
have seen red-tailed hawks flutter, but they're the opposite of kites;
I see red-tails a lot more frequently but have seen one flutter only
once or twice.

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.

-- 
Mickey P. Rowe     (mrowe@lifesci.ucsb.edu)