Gregg, many thanks for the 'sonic postcard' there. Ive been meaning to write 
one for some time now and you have inspired me!

Having moved earlier this year from Manchester to Skipton, in North 
Yorkshire, Ive been having a lot of fun getting myself acquainted with the 
soundscape.
Skipton is a thriving and busy market town, described by the local council as 
'the gateway to the dales'...quite often full to capacity of tourists!
I live in a small terrace, just outside the town and just three houses away 
from me is the Leeds-Liverpool canal.
A regular and welcome sonic friend, then, is the put-putting of the diesel 
engines of many Narrowboats and Barges as they pass by and into the town.
At the other end of the street is one of the main roads into Skipton, but it 
is by no means a noisy one...there are days when I hear no cars at all. 
Parallel with the road is the railway leading to the nearby station...a 
freight train passes through regularly, laden with open trucks full of coal, 
or some other aggregate. Often it will sit in the station, late at night, 
humming, clicking and ticking, like some enormous animal at rest.
Its quite interesting, sat in my back yard, listening to the sounds of these 
two forms of transport at either end of the street. At times, this little 
soundcape may be very similar to what it was 100 years ago, I reckon.
In the town, Skipton Church rings out the hours and on Sunday we are treated 
to an hour or so of some quite elaborate peals. We don't always hear this, 
but sometimes, if the wind is favourable, the sound will blow along the canal.
Opposite the canal, at the point where I live, is the local park and 
municipal golf course, where I walk my dog.
To the back of this park is Skipton auction market, and on auction days, the 
voice of the auctioneer, already distorted by the PA and the reverberant 
acoustics of the huge market halls, bellows out and across the valley in some 
very unusual sounding snatches. Sometimes it sounds like a voice, at other 
times it is quite musical and there are some sounds which are very difficult 
to classify!
In the town, there is a castle, which has a beautiful little woodland around 
it, where I also walk the dog. Ive been doing some recording in there.
Im working on some ideas for a composition at the moment, but I have been 
very interested in the sounds produced by hoverflies.
Hoverflies are those little hovering flies which look like wasps, but are 
perfectly harmless (and very beneficial to gardners and farmers alike). There 
are many types, and Im no expert!
However, if you get into a sunny, dappled part of a wood (although any spot 
will do, I suppose),
you will often see them darting about, having little aerial dogfights with 
each other.
Now, sometimes they stop and rest for a moment on leaves, or some other sunny 
spot. If you spot one on a leaf...go up close and have a good listen. If you 
have never heard this, then I wager you will be pleasantly surprised. The 
hoverfly emits a pure tone, which rises quickly in pitch until a final climax 
where the fly buzzes and lifts off.
If there are enough hoverflies about, you can hear all sorts of weird and 
wonderful harmonies and distortions once you 'tune in' to the sound they are 
making.
I was fascinated by this sound, and wanted to know more about why they made 
it, so I wrote to Dr Francis Gilbert of Nottingham University, an authority 
on hoverfiles, and this is what he wrote:
"Hi Rob !  Very pleased to get your email. Hoverfly sounds are very 
interesting! I have written a paper on thermoregulation that discusses them 
(the 1984 Oikos paper on my website), and years ago I collaborated with a 
filmmaker (Alastair McEwan) who was filming for a natural history series on 
animal adaptations. He filmed some Syrphus ribesii in infra red, sitting on 
leaves and warming up, which is what they are doing. I think he still has the 
film, but it wasn't used in the film, as it turned out. You can hear the 
pitch rising as their thoraces get hotter. They are astonishingly loud at 
times, and where males gather in groups it does sound like an orchestra 
tuning up (as I mentioned in my little book on hoverflies!). Almost certainly 
they are not communicating by sound, but it is a by-product of keeping their 
muscles warm and ready for action, which is to fly after and catch females 
for mating. Immediately they land, the pitch is low because the air currents 
created by flying have cooled them down and the heat from active muscles has 
been switched off. Some people do still believe that they communicate by 
sound, but the evidence is non-existent. Some have thought that they use 
leaves for amplification, but again there is no real evidence that this plays 
any role at all.

Different sized species will produce different pitched buzzes, and body 
temperature alters pitch too. A futher context of sound production is among 
the hoverfly mimics, which can produce a terrifically threatening buzz when 
they are threatened themselves. There isn't a lot published about this, 
merely the statement that they do it. One paper published obscurely in the 
USA measured the pitch of the flight tones of a wasp and its hoverfly mimic, 
and a honeybee and its hoverfly mimic, finding that they corresponded."

I wrote back, speculating that perhaps the flies were battling with sound, to 
which Dr Gilbert responds:
"There is still the possibility that they may be engaging in sound warfare. 
It's just that there's no evidence, but that just means that no-one has 
investigated it.  It would not be inconceivable, since froghoppers do just 
that in ultrasound, but it would be unusual for Diptera. Lovely idea though ! 
"

So, it would appear that our insect friends are just as guilty of noise 
pollution as ourselves, this sound being (as far as we can tell) the 
by-product of an industrial process (ie the heating of a body)!
The point of all this is that, I escaped to the countryside to get out of the 
noise polluted city and now that Im here, Im finding that a little pollution 
is actually quite a nice thing!
Well, this has been a long message, but for those who stayed until the 
credits, I thank you.
Good sounds
Rob Rowlands

.o[±]±][±±][±


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