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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