I don't think Bill Evans is on this discussion list. He could talk about th=
is
much more adequately than I can (the details of Bill's projects can be foun=
d
at <www.old bird.org>), but having worked with him the past two spring
seasons I do know something of the issues involved. Not only does no "voice=
recognition" software to identify bird vocalizations exist (except for a fe=
w
species used as "laboratory rats" to perfect the technique) but it almost
certainly never will. It isn't that the technology isn't available, it is,=
much of it developed by Bill. It is simply impractical. To accomplish such =
a
program, even just limited to the 900 species or so found in North America=
north of Mexico, would require hundreds of people working hundreds of
thousands of man hours. And the market for such a product? No where even
remotely near to covering the expense. Never mind the other 9000 species in=
the world, a significant portion of whose vocalizations are unknown and
unrecorded.
Bill has pioneered the study of nocturnal flight calls of migrating birds.=
Just this year he and Michael O'Brien published a CD ROM with the flight
calls of 250 species of North American migratory birds. Programs have been=
written to detect and record several species (and that's just for the fligh=
t
calls; most species of passerines may have 5-30 other vocalizations plus an=
infinite amount of individual variation). For the past three spring seasons=
Bill has monitored the nocturnal flight calls of Dickcissal, a species whos=
e
flight call is quite distinctive and relatively easy to write a program to=
recognize. We have a transect of 14 stations across south Texas that Bill's=
earlier work suggested probably intercepted the great majority of the world=
's
population of the species during its spring migration. It is also a species=
of concern and worth monitoring because of its habits on its wintering
grounds. Essentially the entire world population winters in northern South=
America, mainly in Venezuela, in what amounts to one enormous flock. Not
surprisingly it can be a serious agricultural pest in these areas as hundre=
ds
of thousands of birds may descend upon a small grain growing area. An
effective control campaign mounted by South American farmers could literall=
y
drive a relatively common species to the brink of extinction before we even=
knew it was in trouble.
The program we use starts up at a preset time (20:30), recognizes and recor=
ds
each Dickcissal flight call it "hears", and shuts down at 05:30. A typical=
night in late April may detect 1000 or more birds in a flight over one
location. Some of these will be false detections. Various sounds sufficient=
ly
close to the Dickcissal call in quality may be detected by the program, as=
may certain mechanical noises (especially rain drops hitting the mic
apparatus). After downloading a night's detections we examine the
spectrographs of each one. It is relatively easy to differentiate between a=
positive (Dickcissal) detection and a false one (Indigo Bunting calls,
certain notes in Purple Martin dawn song, some insect and/or frog noise,
mechanical noise, etc.). Bill also has a "sparrow and warbler" program.
Flight calls of 30 or more species of sparrows and warblers are so similar =
to
the human ear that they can't be identified in the field or from a recordin=
g.
The apparatus works similarly to that in the case of the Dickcissal except=
that potentially 30 odd species could theoretically be detected and recorde=
d.
These can be identified in the same manner. Each spectrograph can be compar=
ed
with known identity graphs and confidently (usually) be identified to speci=
es
and quantified.
This is an over simplified view of the process. The day when one can point =
a
microphone at a vocalizing bird and get a digital readout identifying it wi=
ll
never be a practical reality in my opinion.
John Arvin
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