Hi Dave
It was suggested that I write the note to birding-aus be/c the question had
been raised about the reliability and completenes of Eremaea Birds surveys.
Don't worry - I hadn't read any criticism into any comments - in fact I thought
that the writers had a good understaning of the issues involved. My intention
was simply to make it clear how EB works now. If this elicits suggestions for
improvement, all the better.
With regard to your suggestion, I have tossed this and similar ideas around for
a long time, but have not been able to come up with a solid alternative to the
raw reporting rate. I have two general problems with the approach you describe.
Firstly, the cutoff would be arbitrary, and would have to be scaled according
to the region. Also, how would you distinguish between really poor sites well
surveyed and better sites only briefly surveyed? Or between counts conducted in
good conditions and atrocious conditions? Or between counts conducted at higher
altitudes in mid-winter with those in summer? All these surveys may have had
equal effort, but some might be excluded from the new calculation simply
because they fell below the cutoff. Another possibility is to ask observers to
estimate their survey effort, e.g. in hours, and only include those surveys
with a significant effort, e.g. over one hour, but you are still left with
significant biases (comparing one-hour with 24-hour surveys) and uncertainties
(is my one-hour effort comparable to yours? - I might have just been casually
observing whilst having lunch).
Secondly, if the resulting calculation is complex, it will be difficult to
explain in simple terms to the casual reader. Despite its apparent drawbacks,
the raw reporting rate is readily understood.
Another reason to stick with the raw reporting rate is that the bias towards
scarce species is at least reasonably consistent within a region, so that even
if the reporting rate for Pectoral Sandpipers is inflated over "reality" at
most sites, at least it is consistently inflated thus allowing you some basis
of comparison between sites. In other words, the reporting rate will still help
you find the best sites for Pectoral Sandpiper.
Many thanks for your comments - I greatly appreciate the discussion.
Richard
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