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Hi All,
The value of recordings is of course, dependent on
what the survey is attempting to do. Clearly, they are OK for demonstrating
presence of species, but generally much less useful for estimating populations
and particularly for monitoring changes in numbers over time.
I would imagine that for Ground Parrots, however,
where small populations tend to be spread over fairly large ares of open
grassland/sedgeland, and where most birds call at dusk, strategically
placed call recorders should work OK.
In the mid 1990s, when COG members first
embarked on the (still on-going) bird studies organised by my son David at ANU,
the week or so of bird observer surveys in marked sites was followed up with
timed bird call tape recordings in the same sites. These I played back on a high
quality tape recorder at home and recorded the number of calls
(actually individual notes) made by each species. David was actually exploring
the use of recordings for monitoring.
It transpired that there was not a great deal of
correspondence between the birdwatchers counts and the tapes. This raised the
question as to whether the elapse of time between the two surveys was a
critical factor. David and his biostatician colleague Ross Cunningham organised
a Calibration Study which David and I did over 6 days in Blundells Ck and Warks
Rds in Namadgi NP in Spring 2002. We did simultaneous recording and
monitoring and subsequently compared each of our results with the recordings and
one another. More species were recorded from the tapes than either of us
recorded during our observations. David recorded about 10% more species than 1,
but 30% to 50% more individuals. Clearly, those extra 24 years
matter!
The lack of counted numbers is an obvious defect of
automatic call recording where numbers are important, together with the fact
that birds that call a lot (cockatoos, currawongs) are likely to be
over-recorded whilst others (some robins, raptores) under-recorded or missed
completely. I believe that in David's surveys in the Central Highlands in
Victoria where some sites are virtually impenetrable, some use is still made of
recordings.
Some papers were written on this work. If there is
any interest, I can get the references.
Cheers,
Bruce.
PS The area where we did the Calibration Study was
full of the most wonderful birds, but was very badly burnt in the 2003 fire. I
take a COG group out there every January. It's coming back - but
slowly!
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