Many thanks to the several people who wrote off-line and on-line with their
thoughts about this.
John Leonard contemplated:
> 1. With the loud noise we can't hear bird calls so well, so we have
less
> luck with spotting them
> &
> 2. birds actually avoid areas with loud cicada noises because they
can't
> hear very well and therefore that area would be dangerous for them.
I'm sure both of these situations would apply in some conditions.
In this instance, I presume 2 above to be the case. The phenomenon occurred
in a location where the avifauna is well known and is regularly watched on a
day to day basis. So we tend to have a good feel for what is where, what
normally belongs or occurs here, and where it usually is (up to a point). I
feel comfortable in asserting that during the cicada times, the birds were
significantly fewer in number, rather than just harder to locate aurally.
The questions I'd really like an entomologist out there to help out with
include for example:
1 Do we know the nature of this familiar chorus, its function?
2 Is it thought of as primarily a case of cicadas calling en-masse "Here I
am, choose me" to other cicadas, while at the same time serving to disorient
birds, or perhaps only a case of sounding unpleasant or cacophonous to
birds, sufficient to keep them away? (Or of course, a combination of the
two).
3 At what stage in the cicada life-cycle does it tend to occur? Is it when
they are breeding/mating, or maybe when they've hatched?
4 When there has been a big hatch, might the chorus serve to protect some
species from predation at a vulnerable stage?
Of course, I'm just making all this up, so it could well be none of the
above, something else again!
Any takers please?
Bill Jolly
"Abberton",
Lockyer Valley, Queensland.
Visit our website at http://www.abberton.org
Email:
Ph: (+61) 7 4697 6111 Fax: (+61) 7 4697 6056
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