That's all true, Rob. Except that the dense vegetation that gibbons
typically hang out in consists of a wide variety of landscape,
geological, and organic conditions...far different from the temperate
zones we live in... and although one can get pretty close 25 - 100m,
and where one can sometimes draw a pretty good bead on point source
(especially when they're in sight), the acoustics in many tropical and
subtropical habitats of the world are rarely, if ever, wikipedia-
optimal. And, primates, like some birds, sometimes have a way of
vocalizing that gives the impression that the calls are coming from
one direction (like a ventriloquist) when they actually coming from
another...a false reading picked up in recordings, as well. On top of
that, gibbons, especially when "duetting," will sometimes choose to
vocalize in the most reverberant parts of the forest as do other
primates (like baboons). Good examples of these phenomena can be found
on three of our titles: "Rainstorm in Borneo," "Sumatra Days/Sumatra
Nights" for gibbons, and "African Safari: Zimbabwe" (about 5 minutes
into the track) for baboons. These can be found at http://www.wildsanctuary=
.com/wildstore/soundscapes.html
. Having tracked the critters in each of these cases and having had
them in sight, of course we knew their location and distance. Unlike
most of the habitats we are more familiar with, tropical rainforests
pose acoustic problems we've never even thought of...although the
folks and critters who live there and who are more closely connected
with the natural world around them instinctively understand principals
we may never get to.
Bernie
On Dec 17, 2008, at 7:46 PM, Rob Danielson wrote:
> Hi Bernie--
> I looked into the physics of the variables you
> raise. I'm assuming that Marc wants to locate the
> Gibbons at a pretty good distance. According to
> wikipedia,
> http://en.wikipedia.org/wiki/Speed_of_sound
> extreme differences in humidity between the mic
> paths could create differences in the speed of
> sound as much as .6%. At a distance of 2000
> feet, that would be an error of 1.2 feet,
> maximum. A 9=B0F difference in temperature between
> the mic paths could change the speed of sound as
> much as 3 meters per second and throw off the
> measurement around 7 feet at a distance of 2000
> feet. These seem to be workable variances.
>
> From my experience, the differences in the
> landforms that shape the mic paths can actually
> aid in localization by adding unique, consistent
> complexities to each signal. With three mic
> monitoring, you might not have to triangulate or
> compute the location every time; one might learn
> to recognize the timing difference/acoustic
> difference patterns of frequent calling locations.
>
> 3-D localizing would raise some serious
> challenges-- especially in very hilly/mountainous
> settings. I suppose the X-Y lateral mics need to
> be at the same altitude,.. wouldn't the Z mic
> need to be a considerable distance above the
> canopy to provide enough reference? A ridge
> towards the middle of the triangle might be
> beneficial but not so high as to obstruct distant
> sounds. Rob D.
>
> At 8:31 AM -0800 12/17/08, Bernie Krause wrote:
> >Because gibbons typically call from the canopy and live in a 3-D
> >environment (as opposed to a plane), Rob, one would need to set up a
> >tetrahedral (pyramid w/ all mics equidistant from one another) in
> >order to approximate location. But because the rainforests where they
> >reside (Sumatra and Borneo in my experience) are so reverberant, one
> >would get complex arrival times at each mic obviating precise
> analysis
> >of location. To further complicate matters, the acoustics of these
> >biomes are in constant flux, changing rapidly with the slightest
> shift
> >in temperature or humidity or time of day. That said, if one has
> taken
> >careful measurements over time under different conditions, one might
> >be be able to approximate both distance and location assuming well-
> >calibrated gear that one can rely on under those conditions.
> >
> >Bernie
> >
> >On Dec 17, 2008, at 8:20 AM, Rob Danielson wrote:
> >
> >> At 7:51 PM -0500 12/16/08, Marc Myers wrote:
> >> >Anyone have experience locating animals by measuring distance and
> > > >direction of their calls in natural environments? Gibbons often
> live
> >> >in difficult terrain, at low densities and in small family groups.
> >> >They can be hard to see in their native environment and are
> >> >critically endangered through the majority of their range. Making
> >> >population estimates is important in conservation planning, when
> >> >advising local governments on forestry use and establishing
> risks to
> >> >extinction. Gibbons have famously loud and expressive calls,
> >> >typically sounded first thing in the morning. Populations are
> >> >presently estimated based on the frequency, direction and apparent
> >> >distance of the calls. Of course even experienced listeners are
> not
> >> >very good at estimating distance and as a consequence population
> >> >estimates vary wildly from environment to environment and
> researcher
> >> >to researcher. Any thoughts?
> >> >
> >> >
> >> >_
> >>
> >> Hi Marc--
> >> Here's another "wild" scheme. If pinpointing where the calls/
> animals
> >> are located is really important, one could record with 3 omni
> mics in
> >> a large, equilateral triangle layout. I'm not sure what distances
> >> between the mics to recommend but 500 feet or more would probably
> >> provide enough accuracy to identify their favorite calling spots in
> >> audible range with certainty, maybe even determine that animals are
> >> on the move. You'd need to know the exact distances between the
> mics
> >> and record all three tracks at once. Arrival time differences are
> > > easier to measure (and hear) with percussive calls than sustained
> >> ones and that might be an drawback with Gibbons. One could use
> >> wireless transmitters (a hit, quality-wise) but an option if
> running
> >> wire isn't possible. Rob D.
> >> --
> >>
> >>
> >>
> >
> >Wild Sanctuary
> >POB 536
> >Glen Ellen, CA 95442
> >707-996-6677
> ><http://www.wildsanctuary.com>http://www.wildsanctuary.com
> ><chirp%40wildsanctuary.com>
> >Google Earth zooms:
> ><http://earth.wildsanctuary.com>http://earth.wildsanctuary.com
> >SKYPE: biophony
> >
> >
> >
>
> --
>
>
>
>
Wild Sanctuary
POB 536
Glen Ellen, CA 95442
707-996-6677
http://www.wildsanctuary.com
Google Earth zooms: http://earth.wildsanctuary.com
SKYPE: biophony
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