http://groups.yahoo.com/group/BIRDING-NZ/messages/5901?xm=1&m=p&tidx=1).
Well, this paper may re-ignite the debate. Kate Grarock and colleagues in Canberra, Australia, using long-term data on bird abundance in and around Canberra, collected for almost 30 years by the local ornithologists' group, examined whether mynas there have a negative effect on native bird species. They use some fairly sophisticated statistical analyses to extract the patterns from their large data set (many of you may want to skip these details), but their conclusions seem clear: mynas are not benign; they have negative effects on a wide range of cavity-nesting and small-bodied native species (but not on large-bodied ones). Nevertheless, the authors are more equivocal on the question of whether trying to manage this species is a priority (a point that arose in our own discussions in 2007). But judge for yourself. The paper is:
Grarock, K., Tidemann, C.R., Wood, J., and Lindenmayer, D.B. (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 7(7): e40622. doi:10.1371/journal.pone.0040622
Abstract: 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 (Acridotheres tristis). 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.
See the full paper or download a copy at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040622
Beyond this particular debate, the paper also illustrates the value of long-term data, collected systematically by ordinary observers using consistent methods, to reveal the changes that are occurring, albeit at rates that we might not immediately notice. If you are interested, why not take part in one or more of the Ornithological Society of New Zealand’s various recording schemes (including eBird for general recording)? Details at http://osnz.org.nz/.
Now I'm off to my bunker to dodge the flak
.Peter
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