Geoffrey is correct, the change in bird fauna cannot be attributed to Indian Mynahs based on the study and the data in the paper. At best all that can be said is that there is a correlation between the observed changes in avifauna and the distribution and abundance of mynahs. A well designed replicated experiment comparing treatment (areas with mynahs with areas without mynahs, would be required) - or a comparison of changes in avifauna at sites where mynahs were greatly reduced in density to areas where there was no reduction. There have been many changes in Canberra's avifauna since I arrived in 1974, 6 years after the first mynahs were released. Since then mynah numbers increased but there were many other changes,. In 1974 currawongs were winter migrants - few bred in the city; galahs were rare, as were crested pigeons and corellas, while starlings and sparrows were very common with large flocks roosting during winter in Civic and Manuka as well as being common in the Jerrabomberra Wetlands and Tidbinbilla. There has been a massive change in the abundance of these species since then, changes that have coincided with the increase in mynahs. However, while these events are correlated, I doubt that anyone would attribute the changes in these natives to the increase in Indian Mynahs. I recall some work that David Purchase undertook in around his suburb of Macgregor from the 1960's (for those that do not know David, he was the Director of the national Bat and Bird Banding Scheme). David recorded a steady increase in the variety and density of many native birds after the suburbs were first settled. He postulated (correctly I believe) that as the suburbs aged there was a major increase in the quality of habitat and the availability of food for native birds (both from exotic and native plantings). This is not all that surprising as many new suburbs were built on old grazing land. I suspect that currawongs now breed in Canberra because of the availability of nestlings for their chicks (both native and exotic such as mynahs) although a replicated experiment would be needed to test this. Hence summer breeding of currawongs in Canberra could be interpreted as a sign of a healthy avifauna that can now support the breeding of these birds.
Nevertheless, I believe that the basic conclusion of the paper is correct, that there is little evidence that Indian mynahs are as damaging to native avifauna as was previously believed. Even the conclusion that mynahs have slowed the rate of increase of species such as sulphur cresteds and crimsons is dubious. Both are common and cannot keep on increasing at the rate they have been as they will eventually start to run out of resources causing the populations to slow and possibly decrease - even if mynahs were having an influence.
The crucial issue with managing invasive species is to focus on the desired outcome from management not on pest reduction per se. The question needs to asked, what are the social, production and/conservation outcomes that need to be addressed through management - decline in certain native species, reduced production from orchards or social amenity? Then we should ask what are the factors influencing these desired outcomes from management, invasive species (weeds and pest animals) are likely to be one factor but invariably there will be other factors such as loss of the quality of habitat due to clearing, over grazing (by natives and exotics), impact of global warming and reduced rainfall, or changes due to increased firing of habitat for hazard reduction. Too often in the past we have take\n the easy route and quickly blamed exotic species for all the ills without stepping back and taking a broader perspective. Sure many invasives cause damage and I wish that they were not here, but if we put all our eggs in one basket and focus only on exotics, then we may still lose native species due to other factors. To illustrate this, David Pridell showed that a small percentage of mature foxes knew when mallee fowl chicks were about to hatch and they predated heavily on them. Following intensive fox poisoning there were more chicks hatched but most did not reach maturity. Further investigation showed that the seeds of native grasses that the chicks fed on were rare due to past grazing. If he had stopped at intensive fox management, then there would still have been no recovery in mallee fowl. There are many other similar examples.
For more information on how best to manage the damage due to invasive species, members might like to download and read the recently released ACT Pest Animal Strategy 2012 - 2020: http://www.environment.act.gov.au/environment2.
From: Geoffrey Dabb [
Sent: Friday, 10 August 2012 2:43 PM
Subject: FW: [canberrabirds] The Common Myna: 'Is It Benign or Is It a Pariah?'
I have read this article 3 times and I am unable to see how it shows the Common Myna is responsible for a decline in small birds. Small birds may have declined over the period but where in the opaque maths is it shown that the myna must be the reason? Below is a random cut/paste of articles on overall bush-bird decline, including one suggesting the NOISY MINER (expanding in Canberra) is a reason. [In fact, as I read the piece, it suggests that small birds are INCREASING LESS RAPIDLY in Canberra gardens because of the myna]
THREATENED AND DECLINING WOODLAND BIRDS IN THE NEW...
File Format: PDF/Adobe Acrobat - Quick View
by JRW Reid - 1999 - Cited by 110 - Related articles
standout Declining bird species in the SWB. All but two of the 20 Declining species are passerines or 'typical bush' birds. This contrasts with the 38 Threatened ...
1. Native bird populations declining rapidly - The 7.30 Report - ABC
21 Oct 2009 – It is well documented bird populations are in serious decline across the ...LISA WHITEHEAD, REPORTER: The Australian bush without the call ...
The effect of Noisy Miners on small bush birds: an unofficial cull and ...
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by SJS DEBUS - Cited by 3 - Related articles
... in each time period. Totals for small (<120 g) bush birds, mostly ... are a major contributor to the local decline of many woodland birds. The results also affirm ...
3. Bush Birds
Although none of the bush bird species at Sydney Olympic Park are listed under threatened species legislation, many bush birds are in severe decline across ...
File Format: PDF/Adobe Acrobat
Australia's bush birds are in trouble. Only one ... regions are in decline, and more species will vanish if ... causes and extent of bird declines across the southern ...
5. No birds in the bush
www.birdlife.org › BirdLife News › News Archive Search
01-06-2010. Australia's woodland birds, including many species generally regarded as common and widespread, are declining at an alarming rate according to ...
From: Paul Fennell [m("grapevine.com.au","ptf");">]
Sent: Friday, 10 August 2012 2:22 PM
To: 'David McDonald (personal)'; 'CanberraBirds'
Subject: RE: [canberrabirds] The Common Myna: 'Is It Benign or Is It a Pariah?'
I am most interested in further information on the Striated Paradoxes mentioned in the abstract. A problematic species I am sure.
(Striated Paradoxes, Rufous Whistler, Willie Wagtail, Grey Fantail, Magpie-lark, House Sparrow, Silvereye, Common Blackbird).
Editor Annual Bird Report
COG Databases Manager
From: David McDonald (personal) m("dnmcdonald.id.au]","david");">[
Sent: Friday, 10 August 2012 9:39 AM
Subject: [canberrabirds] The Common Myna: 'Is It Benign or Is It a Pariah?'
Readers of the Canberra Times will have seen the article about Kate Grarock's research on Common Mynas in Canberra.
The paper to which it refers is Grarock, K, Tidemann, CR, Wood, J & Lindenmayer, DB 2012, 'Is It Benign or Is It a Pariah? Empirical Evidence for the Impact of the Common Myna Acridotheres tristis on Australian Birds', PLoS One, vol. 7, no. 7, p. e40622.
It is available in free full text at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0040622 .
The abstract reads:
There is widespread concern over the impact of introduced species on biodiversity, but the magnitude of these impacts can be variable. Understanding the impact of an introduced species is essential for effective management. However, empirical evidence of the impact of an introduced species can be difficult to obtain, especially when the impact is through competition. Change in species abundance is often slow and gradual, coinciding with environmental change. As a result, negative impacts on native species through competition are poorly documented. An example of the difficulties associated with obtaining empirical evidence of impact due to competition comes from work on the Common Myna (<italic>Acridotheres tristis</italic>). The species is listed in the World’s top 100 worst invaders, despite a lack of empirical evidence of its negative impacts on native species. We assessed the impact of the Common Myna on native bird abundance, using long-term data both pre and post its invasion. At the outset of our investigation, we postulated that Common Myna establishment would negatively affect the abundance of other cavity-nesting species and bird species that are smaller than it. We found a negative relationship between the establishment of the Common Myna and the long-term abundance of three cavity-nesting species (Sulphur-crested Cockatoo, Crimson Rosella, Laughing Kookaburra) and eight small bird species (Striated Paradoxes, Rufous Whistler, Willie Wagtail, Grey Fantail, Magpie-lark, House Sparrow, Silvereye, Common Blackbird). To the best of our knowledge, this finding has never previously been demonstrated at the population level. We discuss the key elements of our success in finding empirical evidence of a species impact and the implications for prioritisation of introduced species for management. Specifically, prioritization of the Common Myna for management over other species still remains a contentious issue.
Regards - David
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