This on-line article Published in the journal PLoS One (see
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040622,)
is most unfortunate. If you read it at all, I recommend great scepticism.
This study uses data from the Garden Bird Survey (GBS) but severely
misrepresents the way the data were collected. For that and several other
reasons, I believe this study is multi-flawed. I am the author of the book
"Canberra Birds: A Report on the first 21 years of the Garden Bird Survey",
(in short The GBS Report) which I regard as a fitting tribute to all those
who have contributed to the Garden Bird Survey (GBS). This book is a
detailed analysis of the history, methods and results of the GBS that has
been run by Canberra Ornithologists Group (COG) in Canberra, since July
1981. On a personal note, I am angry that this myna article was released
without being checked and verified (by someone who knows, such as me) as a
true representation of the data methods of the GBS.
The GBS Report is cited in this on-line article but clearly was not
consulted properly let alone understood. The article then goes on to make
several major errors in understanding the data framework.
The way it states the GBS was run (stating it as fortnightly surveys of 20
minutes) is a nonsense. It is and always has been since 1981, data collected
on a weekly grid, for unlimited time (i.e. up to 10080 minutes per week,
even though many observer weeks would be only from one to 10 minutes of
effort). This is clear from any one of the something close to 2000 GBS
charts that have been printed, let alone the full description of the methods
and history of The GBS Report. It says "a total of 74 492 surveys was
undertaken in the survey area over 29 years". Not so. The GBS in its
totality is ONE survey. 74 492 is simply the number of observer-weeks (up to
year 29), which is a week on a chart with a record for at least one species.
That is not a survey. They describe the survey area as 3.142 ha, as though
all the contributors have uniformly selected the size of the area to 4
figures of significance and all equally keep to that area for all species.
The best that could be said is that observers variably set a survey area
based on the recommended 100 metre radius, but as this is a volunteer survey
and in the first 12 years this 100 metre radius instruction was very vague,
this is far from consistent. There is little if any understanding of the
geographic or time issues involved, or the way that the survey has evolved.
The way they have used the data after subdividing the area geographically
over time is I think ridiculous, given the way that distributions and
numbers of observers has changed substantially over the years. There is
little attempt to explain the wonky ideas proposed and used, such as why
they translate a 100 metre radius to a square kilometre, as though habitat
spread is even, which it is not and even if it is, it is highly questionable
that every species has been equally counted to the same area. There is
little attempt to justify the rationale behind the species chosen to be
analysed. It seems unaware that there is a huge range of factors impacting
separately or together on every species, that influence perceived changes in
status (not just the addition of another species). Perceived meaning real
and then as revealed after imposition of survey biases. I submit that the
analysis is way over the top mathematically, doing calculations that go way
beyond the real usability of the actual data. To call the article "Empirical
Evidence" is way beyond the truth. At best all that can be said is that
there is some correlations in time between the observed changes in the
distribution and abundance of mynas and other avifauna. To an extent some of
the analysis and conclusions are of interest.
The SMH article mentions: the results show that even when taking into
account the capital's urbanisation, the myna's arrival has reduced numbers
of cavity-nesting birds such as the sulphur-crested cockatoo, crimson
rosella and laughing kookaburra. Yes the Kookaburra has declined but the
Sulphur-crested Cockatoo and Crimson Rosella have had consistent and
significant increase in abundance throughout the period. The Eastern Rosella
has been remarkably stable and the Red-rumped Parrot has been variable.
How do these conclusions from the article make sense? "The abundance of the
Common Starling appeared to increase after Common Myna establishment. Common
Starling abundance declined throughout the survey period. We found no
significant negative relationships between Common Myna establishment and
Common Starling abundance." It is abundantly obvious that the Common
Starling decreased as the Common Myna increased, that is described in The
GBS Report as the most likely relevant interaction to any other species by
the Myna. And what about the activities of Canberra Indian Myna Action Group
Inc (CIMAG see indianmynaaction.org.au) and the culling program of Mynas
being run and the huge reduction in Myna numbers that it has achieved in
Canberra in recent years such that the rise in abundance has been halted and
reversed. (So Carl we certainly do have a control measure.) Why is that not
mentioned? Why is there no discussion of reversal of trends on other species
occurring along with the success of this program?
Lastly I will mention you can do any level of calculation you like with any
set of numbers. I expect that this same analysis would find a strong
connection between the numbers of Common Mynas and the number of mobile
phones or that the numbers of Common Mynas had no impact on the number of
vintage cars. The analysis might have a strong basis if all sites had been
equally surveyed by the same methods for all species equally over all years.
Not one of these aspects is correct. By all means read this article but with
caution or with The GBS Report to properly explain the context of the data.
Philip Veerman
24 Castley Circuit
Kambah ACT 2902
02 - 62314041
Dear B-A,
There is a piece in the Sydney Morning Herald's web site regarding a study
on Common Mynah and their effects on native bird species.
http://www.smh.com.au/environment/conservation/pushy-myna-birds-a-major-nest
-pest-20120812-242v2.html The study was based partly on data collected by
the Canberra Ornithologist's Group. Now that we know they are a pest, it
would be nice to come up with a control measure - that's the rub.
Cheers,
Carl Clifford
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