Hello Paul,
The items of the comparison between abundance and recording rate is
discussed in intimate details over several pages (in the 21 year editions,
mainly pages 29-34 and 45-46) in The GBS Report, over a range of many
species. I suggest you have a look. Ignore BOCG, as it has nothing of value
in regard to understanding the survey. Indeed I identified this very aspect
as the main highlight of the GBS system, because it is so important to
understand bird surveys and few other surveys have the structure to examine
both items in parallel. A few (but not many) other studies examine the same
thing. So the answers are all there. Indeed the Koel is a really good
example to chose on which to look at this aspect because it is one extreme
of the range. As such I don't know if really quite remarkable is the right
term. It is completely predictable based on the relevant features of the
bird.
Yes of course the two graphs go in tandem (for this species but very
obviously do not go together for several other species). The major part of
the examples in The GBS Report discuss monthly abundance patterns rather
than long term, but that is because I considered that to be more interesting
and I had easy access to both. However the situation is almost exactly the
same in regard to long term trends as for seasonal changes.
I also suggest you could easily have gone further back than 2005.
This issues are:
Koels are normally noticed in singles or small numbers, thus simply by
mathematics the two graphs must match. Any species that occurs potentially
in large numbers (high G in GBS speak), then there is far more room for
variation between recording rate and abundance. Again simply by
mathematics......
Koels occur almost totally in one habitat type (in our region, this is
suburbs) that are well represented in GBS data. This has been stable. Thus
there is little if any sampling bias difference between general records and
GBS A values. So clearly there will be a match.
Koels are really obvious birds and so there is little bias of poor recording
that might apply to less obvious species.
Once again this really highlights a need to update The GBS Report. I would
really like to do that. (Except not at my personal financial expense)
Philip
-----Original Message-----
From: Paul Fennell
Sent: Thursday, 7 April, 2016 2:32 PM
To: Canberrabirds
Subject: Eastern Koel
Hello everyone
I hope we are all getting more sleep now that most if not all the Eastern
Koels have gone back east. At least the Pickles Street crowd have left.
In writing up the Highlights and Lowlights section of the Annual Bird
Report, I have been debating whether the increase in Koels in the ACT is a
highlight or a lowlight.
I have attached a short statement about their increasing prevalence which
contains a couple of graphs. Unfortunately I am not sure how to include
graphs in email texts with this new iMac system I have, since all I get is a
box with a question mark in it. Thus the resort to including an attached
word doc with the graphs in there.
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