Bill Whan says, "I imagine expert aerialists like shorebirds find it more
efficient to
take flight to avoid trouble than do coots and grebes." I agree - this past
Friday at the Hoover Reservoir boardwalk, I watched a juvenile Peregrine
Falcon unsuccessfully chase a shorebird - it was that lucky. The falcon
rocketed around, would briefly fly out of view then return with steadfast
approach, but sill did not succeed in the hunt. At one moment. one
shorebird flew straight up while it was being pursued and the Peregrine
narrowly missed but quickly put the air brakes on hard, turned around and
dove again at the same bird. This shorebird was very efficient with this
tactic - because it lived. Perhaps this fast shorebird will survive to pass
on its DNA next spring even though the odds are against it.
Further though, I wonder if a Bald Eagle really enjoys spooking up birds,
rather a shorebird is genetically programmed to flee if it perceives any
threat from an above raptor. The shorebird can't afford to take any
chances - is there time for a shorebird to evaluate the level of threat from
say... a kite being flown by an enthusiast of wind, or from a Bald Eagle
which certainly carries the inherent threat that all raptors do? I think
there motto is act now, think later.
Birds' methods of survival, whether it being successful in pursuit of prey
or, on the other hand - escaping becoming energy for another bird for an
example is just one of the many reasons that I enjoy watching birds. Its
pretty amazing out there and I anticipate spending a lot more time watching
shorebirds, and therefore naturally watching shorebirds being taken by
falcons and such, and hopefully something like the above mentioned
Short-eared Owl. That would be amazing. Also Bill cites of Tinbergen's
study of the chicks of Herring gulls freezing when they see certain shapes
overhead. In addition to the chick's (and I'm sure many other species as
well) demonstrated caution immediately upon hatching -I'm sure that they
become even more skeptical of anything overhead as life experiences occur
hence being the main reason that I think groups of shorebirds flush up so
often and easily. The fact that they don't stay put longer on the mudflats
is probably THE biggest obstacle in identifying shorebirds for me.
Glen Crippen
Burr Oak Lake
-----Original Message-----
From: Ohio birds [mailto:[log in to unmask]]On Behalf Of
Bill Whan
Sent: Wednesday, August 29, 2007 4:53 PM
To: [log in to unmask]
Subject: [Ohio-birds] shorebird responses to raptor-like birds
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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Additional discussions can be found in our forums, at www.ohiobirds.org/forum/.
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