Grey Butcherbird

To: Philip Veerman <>
Subject: Grey Butcherbird
From: Martin Butterfield <>
Date: Fri, 30 Aug 2019 20:25:08 +0000
I have confirmed that using A values gives a very similar pattern to simply counting summing the number of birds.  

However I think Philip, is correct in his second paragraph in saying that a high proportion of the increase is due to the same  birds being reported multiple times.  I came to that conclusion after looking at the % of sites at which the species was reported each year (ie F, rather than A),
30 97 GBB.JPG
This shows a much more gradual curve rather than a sharp increase around year 24.  Repeating the approach from playing around with A I projected  a trend in this series up to year 24 forward for 6 years which suggested a value of F of close to 50% - almost exactly the calculated value.

This it would seem that, rather than the fires as a push factor, some pull factor - possibly flying mincemeat - was making it more attractive for the Butcherbirds to hang about.

As one of my bosses used to say "I'm not often right, but I was surely wrong that time".

On Fri, 30 Aug 2019 at 20:36, Philip Veerman <> wrote:

The method that Martin has used “charted the total number of birds reported”. That does not allow for that the sample size of observer weeks (which should be the denominator in any such calculation, is variable (although Martin has chosen to bypass that and it may well be sort of excusably right that that using A values would give a similar pattern). Earlier COG ABR and The GBS report based everything on data relative to the appropriate denominator. Actually the A values are given in the COG ABR but only in a way that it is very difficult to find, because they are not given in the text! As was the case years ago! These data can only be found by scrolling through that long summary table, with no way of indexing it! How dumb…. Too tedious even for the most dedicated.  I have had this discussion before.


However note that there is a huge component in the data Martin has used, of repeat observation of the same birds at the same site on subsequent weeks. In early years the species did not stay around much so there was not much repeat observation of the same birds at the same site. Now they are becoming more resident, so a large part of the increase shown in the graph of data that Martin has used relates that change. As in nowhere near most of the increase suggested is more birds, I suggest although sadly I don’t have the figures, it is mostly or overwhelmingly due more of repeat weekly counts of the same individuals, due to increased residency. As I said The GBS Report needs to be redone so these things can be properly explained in context and alternate interpretations needs to be done in a manner that comprehends the data.


The suggestion of role of fire is interesting.




JPEG image

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