Is It Benign or Is It a Pariah? Empirical Evidence for the Impact of the Common Myna (Acridotheres tristis) on Australian Birds

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.This work is supported in part by the Invasive Animals Cooperative Research Centre and the Australian National University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

The introduction, spread, impact and control of the common myna (Acridotheres tristis)

The common myna (Acridotheres tristis) has been introduced throughout the world primarily to control insect pests in agriculture. However, the common myna has now been listed in the world's top 100 worst invaders. There is global concern that the common myna may negatively impact other species through territorial exclusion and cavity-nesting competition. As such, there is growing demand for management strategies to control the species. Despite this concern, there is limited scientific evidence regarding the impact of the common myna. Some research even suggests the impact of this species is over stated or nonexistent. Therefore, it is imperative that the population dynamics and potential impact of this species are understood. This thesis comprises five research articles that investigate the introduction, spread, impact and control of the common myna. To examine the introduction and spread of the common myna, a composite 41-year data set was used to reconstruct the species invasion sequence. The impact of the common myna on native bird abundance was then assessed, using long-term data both pre and post invasion. A negative relationship between the establishment of the common myna, and the long-term abundance of three cavity-nesting species and eight small bird species, was observed. This finding has never previously been demonstrated at the population level. Using 1071 transect bird surveys, the impact of the common myna in conjunction with habitat modification was then investigated. This study indicated that common myna abundance is strongly influenced by habitat. However, negative associations between common myna abundance and some bird species were also observed. To investigate cavity-nesting competition, 225 nest boxes were established and monitored over three breeding seasons. This study provides the strongest evidence to date for a negative impact of the common myna on native birds through cavity-nesting competition. Finally, the impact of a community common myna culling program was assessed using transect surveys and a population model. Reductions in common myna abundance were related to high intensity culling across small-scale areas. However, the results indicate that too few individuals are being removed to have a broad scale influence. The elements for a successful control program and methods to increase the effectiveness of culling programs are discussed. This thesis provides a comprehensive investigation into the ecology of the common myna and adds significant new knowledge on the invasion sequence, species impact (type and severity) and population dynamics of the common myna. An overarching finding of this thesis is the significant impact of habitat on species abundance. Therefore, to disentangle the impacts on native species, analysis must include both habitat variables and introduced species impact. Habitat modification can also influence the severity of introduced species impact and therefore potential management responses. Habitat restoration is recommended as an alternative method for common myna control that would also aid native species recovery

Euthanasia of pest sturnids in nestboxes

Nestboxes are commonly used as a research tool or for enhancing habitat quality for native hollow-dependent wildlife, but these objectives can be compromised if boxes are occupied by feral species, such as Common Myna Sturnus tristis and Common Starling S. vulgaris. Mynas and starlings exclude other potential nestbox users by actively harassing them, and by accumulating large volumes of nesting material that preclude occupation by other users. Here, we report a system using air-cooled carbon monoxide (CO) from a small 4-stroke petrol engine that enables in situ euthanasia of pest sturnids, eggs and chicks in nestboxes. The activity was earned out after dark, when sitting females were reluctant to fly, and was monitored via closed circuit television, to ensure that non-target species were not affected. Once the adults were euthanased, the entire contents of the box, Including adults, chicks, eggs and nesting material, were dumped, via a hinged base (drop floor), thereby freeing up the box for other potential occupants. We report results from the 2009-2010 and 2010-2011 breeding seasons, during which a total of 48 adult female mynas was euthanased, along with 115 eggs (33 clutches) and 119 chicks (35 clutches). Time to immobility of adults (n = 48) was 96.4 ± 29.4 seconds (mean ± s.d.). Young chicks were far more tolerant of carbon monoxide poisoning than adults and were euthanased, once the box contents had been removed, by placing them in a cloth bag and striking them against a hard object. No starlings were encountered in this trial, but earlier trials with carbon monoxide euthanasia indicate that the method would also work for this (and perhaps other) pest species

Is it benign or is it a Pariah? Empirical evidence for the impact of the common Myna (Acridotheres tristis) on Australian birds.

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

Does Human-Induced Habitat Modification Influence the Impact of Introduced Species? A Case Study on Cavity-Nesting by the Introduced Common Myna (Acridotheres tristis) and Two Australian Native Parrots

Introduced species pose a major threat to biodiversity across the globe. Understanding the impact of introduced species is critical for effective management. Many species around the world are reliant on tree cavities, and competition for these resources