Don Lloyd wrote (9/5/05):
> <snip>
> I believe some critters take advantage of pink noise 'confusing the space=
',
> as you put it. Whilst recording in marshes, I've noticed frogs and red-wi=
ng
> blackbirds (among others) piping up when a jet plane blankets the area in
> pink noise, or when a diesel truck downshifts on a nearby hill. When the =
jet
> or truck fades away, the frog chorus has reached critical mass and contin=
ues
> on its own for a while, only to eventually die down and await the next
> protective, predator-disorienting pink blanket.
>
>
Australia's Albert's Lyrebirds, whose vocalisations I've studied in some
depth, are smarter. They don't waste their energy singing when they can't
be heard. There's very little song from them when strong winds or heavy
rain fill their subtropical rainforest habitat with noise.
Sad that our old mate Walter is no longer a subscriber. I'm almost sure he
once wrote of the adverse effect of heavy noise on some species of frogs
that synchronise their calls thus making it difficult for potential
predators to locate the source of the sound of any one individual. If say
loud aircraft noise drowns out the sound of their calls they get out of syn=
c
and are then more at risk.
Here in Brisbane (Australia) the Bottle Cicada (Glaucopsaltria viridis) is
common in our suburban gardens. Like many cicadas, the males all sing at
the same time, thus making it difficult to locate any one individual. With
just one's ears, that is. Klas's so excellent and highly directional
Telinga mic and reflector make it easy. They sing at dusk: "Continuous
and without apparent variation", is how Dr Max Moulds author of the book
"Australian Cicadas", describes it. But that is not all.
During the day they have a very different and far from obvious call. Just =
a
few (up to 5) short sharp 'bips' over a second or so. Then silence for
several minutes. Also very effective in making it difficult to locate the
insect by the sound. (And incidentally, using Peak LE software and a Mac
computer, I have strung these bips together without spaces between them, an=
d
produced their continuous dusk song.)
To locate one during the day, play a recording of the continuous dusk song,
and the cicada just has to join in. He won't keep going for long after yo=
u
stop the recording, but you can start him again.
The dusk song of course is to attract females for mating. The song changes
if a female arrives. I surmise that the intermittent day song is aimed at
males - to enable each to maintain his personal space. I hoped to test thi=
s
by concealing a small speaker fairly close to a male and playing a recordin=
g
of the spaced out day song. Unfortunately my garden is very small; I'd hav=
e
to use the garden next door. This was a possibility but the house was sold
and the new owners cleared the whole area - all trees and shrubs have gone,
and there'll be no cicadas.
But back to mechanical noise. At one stage someone used a motor-mower with
a whine of just the right pitch to match the cicadas dusk song. And they
joined in!
Cheers
Syd
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