Rare bird sitings along Moonee Ponds Ck [what aboutMerri Ck? - both Melb

To: "Dave Torr" <>
Subject: Rare bird sitings along Moonee Ponds Ck [what aboutMerri Ck? - both Melbourne area]
From: "Richard and Margaret Alcorn" <>
Date: Fri, 9 Feb 2007 14:41:44 -0000
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.


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