Many helpful remarks on and off the list, and a bit of looking around
in publications, prompt the following. Three respondents mentioned the
research possibilities of kites/silhouettes, and this is just what Niko
Tinbergen did in his experiments with herring gulls, learning that
chicks just out of the egg froze when a bird of a certain shape (see Bob
Powell's post) passed overhead, and ignored other shapes (The Herring
Gull's World, 1960; Tinbergen later won the Nobel prize for this and
other ethological studies). Perhaps shorebirds have evolved similar
instincts, as raptors are always overhead on their nesting grounds. One
person told me of watching shorebirds spooking repeatedly at kites used
for body-surfing by human swimmers on a beach.
        Probably somewhere someone has studied which bird species disturb
shorebirds, and which do not, where, and under what circumstances. An
interesting and readable paper with some info is at
elibrary.unm.edu/sora/Condor/files/issues/v077n01/p0073-p0083.pdf  ,
where researchers spent two winters at the famed shorebird spot Bolinas
Lagoon and quantified kills of these birds. Their findings suggest that
the largest threat to wintering shorebird flocks must be raptors, and
that flocking may reduce an individual bird's chance of being picked off
by more than two-thirds. A single merlin accounted for a lot of
shorebird mortality, and kestrels took a toll (the study took place
1971-73, when peregrines were a small part of the picture). Harriers
were not often present, but took shorebirds, even coots. Accipiters,
buteos, and white-tailed kites, though present in the area, played a
very small part. Short-eared owls, however, subsisted on birds for 51.7%
of their diet in one winter and 87.9% the next.  Though less numerous,
long-eared and great horned owls did a lot of damage as well. Surely
owls did not rely on raw speed to catch shorebirds! The researchers
estimated that raptors took 20.7% of the dunlins, 11.9% of the least
sandpipers, 7.5% of the western sandpipers, and 13.5% of the sanderlings
present over one winter.
        I imagine expert aerialists like shorebirds find it more efficient to
take flight to avoid trouble than do coots and grebes. They also seem to
know that an individual by itself is in greater danger, so panic on the
part of one becomes a movement by all. We all have seen the "dreads" of
terns--those mass flights they so often undertake that seem provoked by
invisible threats, or maybe sheer exuberance. And I think Craig's point
is well taken, that birds just passing through will take cues from the
locals as to the danger posed by certain raptors. We can't forget that
this time of year many Arctic shorebirds in Ohio are juveniles traveling
without experienced adults, and may be seeing their first eagles...
        Several people have described redoubtable feats of hunting by eagles,
but none seems worth the trouble for a scrawny shorebird. A haunch of
road-killed deer or filet de carp is so much more satisfying. Sometimes
you get the feeling in the field that eagles delight in throwing their
weight around, actually, just wreaking havoc for the heck of it...
Bill Whan
Columbus

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