CASE STUDY: Common impacts Case Study on the impacts of common (Indian) on other species and the effectiveness of community trapping in

Introduction: This project aimed to investigate:

Common or Indian mynas are now • the invasion history of common mynas widespread throughout eastern in Canberra3 and are considered to threaten native • long-term native bird abundance in biodiversity due to their territorial Canberra before and after common behaviours and nest cavity competition. myna establishment4 The perceived impacts of the • the impact of the common myna in are often based on unreliable information, combination with habitat variation5 and there is a lack of scientific research • the impact of the common myna on 1,2 that confirms the bird’s actual impacts . cavity nesting species6 The abundance of native species • the effect of common myna trapping frequently changes with environmental on their abundance7 factors, including habitat clearing and urbanisation. This means that it is hard Process: to separate the effects of common mynas This project used long-term data and from environmental factors. an integrated approach to provide the Many community trapping programs have strongest evidence to date for the impact been set up in response to the perceived of the common myna on the population negative impacts of the common myna on abundance of some cavity-nesting and native . These programs encourage small bird species4. people to trap and humanely euthanise Bird abundance in Canberra between common mynas. However, there is only 1981 and 2010 was documented based on limited scientific evidence that these long-term survey data, gathered by the trapping attempts reduce the overall Canberra Ornithologists Group (COG), abundance of the common myna or benefit which amounted to a total of 74,492 Project partners native species. Garden Bird Surveys (GBS)3. • Invasive CRC In 2008, the Invasive Animals Cooperative Environmental factors, such as urban • Australian National Research Centre (IA CRC) funded a PhD development (eg dwelling and human University project undertaken by Kate Grarock using population density) and vegetation • Canberra Ornithologists Canberra as a case study. Prior to this variables (eg native , modified Group (COG) research there was limited understanding urban grassland, dry forest, ) of the impact the common myna had on were taken into account to distinguish • Canberra Indian Myna Action Group Inc the abundance of native species. between impacts of the common myna and (CIMAG) those of habitat change.

1 CASE STUDY: Common myna impacts Case Study on the impacts of common (Indian) mynas on other bird species and the effectiveness of community trapping in Canberra

Abundance and nesting success of common found where lethal controls are used2. Glossary mynas and native cavity-nesting species The apparent success of fine scale culling were also investigated at 15 survey sites indicates that trapping may be more Species abundance around Canberra using 225 purpose-built effective if targeted in areas of greatest The number of individuals nest boxes6. impact. of a species in an area, landscape or Common mynas, habitat change Trap shyness, where birds adapt their and species richness: behaviour to avoid traps8, may also reduce Species richness effectiveness. Some studies indicate that The number of different The research indicated that the common this is more likely to occur with adults species in an area, myna primarily takes advantage of habitat than juveniles9. The common myna has landscape or ecosystem change when colonising a new area. High also been observed avoiding areas where numbers of common mynas in combination shooting occurs7. with habitat change had a negative impact Trapping with decoy birds may enhance on some cavity-nesting and small bird success of valve traps for common mynas, species5. especially where food is readily available. Tree density strongly influenced the Additional control methods, such as abundance of the common myna and nest box trapping and roost trapping7,10 the species was far more abundant in may improve overall effectiveness of urban areas with fewer trees than in trapping to benefit the community and the nature reserves5. There were no negative environment. associations between common myna abundance and total species abundance How should we manage the common and richness, native cavity-nester or large myna? native bird abundance and richness5. Community support is already very Common mynas and cavity nesting strong for common myna management Common myna eggs and chick in a species: in Australia and greater use of science nestbox (above) and Crimson Rosella in community-led projects could further (below) using a nest box. Project results indicated that habitat has enhance management outcomes. The main Images: Kate Grarock a strong influence on the abundance and priority should be to prevent the transport nesting success of the common myna, and establishment of new common myna crimson rosella and eastern rosella. incursions2. At sites with fewer trees, the common The research demonstrated that the myna occupied a high number of nest common myna had both a short lag period boxes (up to 90%) and built ‘fake’ nests before population growth (<3 years) and that further reduced cavity availability6. spreading to new areas (six years)3. This Crimson rosella and eastern rosella suggests it is important to respond to new abundance was lower at these sites. invasions rapidly before the population The negative influence of common myna can grow in numbers and further spread. nest box occupancy on crimson rosella Once a species becomes widespread and abundance was even more dramatic at abundant, total eradication is highly high tree density sites6. unlikely; population control and impact Effect of trapping: mitigation are then the best management strategies3. High intensity community trapping 2 was found to reduce common myna Culls of at least 25 birds per km per year abundance at a local scale7. Over larger are needed or alternative methods for 7 scales, however, natural reproduction, controlling this species will be required survival and/or immigration may limit the (this cull rate relates to the Canberra effectiveness of trapping7, which is often study and population). The common myna

2 is able to compensate for culling through species4,5,6. This will help determine if the rapid reproduction so control programs impacts of an introduced species are more need to be maintained year after year or severe in particular habitats. the species will quickly recover. Understanding the impacts will enable The timing of trapping can have a large targeted management and mitigation impact on the effects of a control program. programs. For example, the impact of the Currently the largest numbers are caught common myna might be more severe in just after the breeding season, when young areas that represent ‘high quality’ habitat birds are easily trapped. However, it would for native birds6. Effectiveness of trapping be more effective to trap prior to and may be enhanced by targeting efforts in during the breeding season, when culling areas where mynas have greatest impacts is more likely to be additive to natural to the environment or community. For mortality7. Trapping from September to example, near breeding areas of superb December would also be more likely to parrots (Polytelis swainsonii), or where reduce the competitive pressure for nest large roosts occur in high use areas (food cavities. courts, churches etc). Several methods of controlling the common The research indicates the common myna myna will likely be required, due to its may prefer using nest boxes to natural adaptable nature11. An integrated approach cavities1,6. Simply providing nest boxes to could include reducing food availability (eg alleviate competition for cavities could dog food), limiting nesting sites (such as lead to an increase in common myna roof cavities), habitat manipulation (tree nesting and abundance if the nest boxes planting and revegetation) and culling in are not actively managed to remove sensitive areas. nesting myna birds10. Modifying current practices (timing of Habitat modification in combination trapping) or using alternative and/or with the introduction of complementary culling methods may also can have significant negative impacts on be required7 for effective control. native species7. The common myna occurs in greater abundance in cities and towns, Implications for control of common and in areas with low densities of native mynas: trees5,6. Human habitat modification can This study showed that habitat needs to reduce the ‘quality’ of habitat for native be considered when investigating the species and lead to an increase in common impacts of an introduced species on native myna abundance. Diagram above: Low tree density, or fragmentation of native Drop-floor nestbox and vegetation, may enhance habitat quality portable micro-euthanaser for the common myna enabling the species system used in this research. The 25 cc 4-stroke engine to spread into new areas and compete delivers air-cooled exhaust for resources with native species1,5,6. For (3% carbon monoxide) via example, housing developments that are a wand that also includes built adjoining threatened species habitat a closed-circuit television would be of significant concern. This camera and screen. This of habitat modification would drive an enables the operator to increase in the abundance of the common view the contents of the myna in sensitive areas, greatly increasing nestbox, thereby preventing the likelihood of negative impacts on euthanasing non-target threatened species. species8,10. www.feralscan.org.au/mynascan/

3 CASE STUDY: Common myna impacts Case Study on the impacts of common (Indian) mynas on other bird species and the effectiveness of community trapping in Canberra

Habitat restoration and tree planting may ( tristis) and two Australian be useful tools to both control common native parrots. Environmental Management, myna abundance and to aid native bird Volume 52, Issue 4, pp 958-970 doi:10.1007/ s00267-013-0088-7 species recovery4,5,6,7. This will not only increase habitat quality for native species 7. Grarock K, Tidemann CR, Wood JT, (including cavity availability in the longer Lindenmayer DB (2013) Understanding basic species population dynamics for effective term), but it is also likely to make the control: A case study on community-led culling habitat less suitable for the common myna. of the common myna (Acridotheres tristis). Without restoring habitat and making these Biological Invasions, Nov 2013. doi: 10.1007/ areas ‘less suitable’ for the common myna, s10530-013-0580-2 attempts to control species numbers are 8. King DH (2010). The effect of trapping pressure only likely to succeed over the short term, on trap avoidance and the role of foraging with the species reinvading once control strategies in anti-predator behaviour of actions are eased. common mynas (Sturnus tristis). Canberra Bird Notes 35(2): 85-108.

9. Conover MR and Dolbeer RA (2007). Use of Further Reading: decoy traps to protect from Common mynas. Image: Luke Pomfret juvenile European . Human–Wildlife 1. Lowe KA, Taylor CE and Major RE (2011). Do Conflicts, 1, 265–270. Common Mynas significantly compete with native birds in urban environments? Journal of 10. Tidemann CR, Grarock K, and King DH (2010). Ornithology 152: 909-921. Euthanasia of sturnids in nestboxes. Corella 35(2): 49-51. 2. Tracey JP, Bomford M, Hart Q, Saunders G and The main priority Sinclair R (2007). Managing Bird Damage to 11. Tidemann C (2005). Indian Mynas — Can the Fruit and Other Horticultural Crops. Bureau of problems be controlled? In: M Hayward (Ed), should be to Rural Sciences, Canberra. Proc. of the 15th National Urban Management Conference, Australian Veterinary prevent the 3. Grarock K, Tidemann CR, Wood J and Association, Canberra Pp 55-57. transport and Lindenmayer DB (2012). Is it benign or is it a pariah? Empirical evidence for the impact establishment of the Common Myna on Australian birds. of new common PLoS ONE 7(7): 1-12. doi:10.1371/journal. More information: pone.0040622 myna incursions. PestSmart Toolkit: 4. Grarock K, Lindenmayer DB, Wood JT, http://www.feral.org.au/pestsmart/ Tidemann CR (2013). Using invasion process Rapid response theory to enhance the understanding and PestSmart Factsheet: Common (Indian) to new incursions management of introduced species. A case Myna (2013). PestSmart Toolkit publication, study reconstructing the invasion sequence of Invasive Animals CRC. http://www.feral. before bird the common myna. J. of Env. Management, org.au/pestsmart-indian-myna/ numbers grow 129: 398-409. MynaScan: and spread is also 5. Grarock K, Tidemann CR, Wood JT, Lindenmayer DB (2013) Are invasive species drivers of native http://www.feralscan.org.au/mynascan important. species decline or passengers of habitat modification? A case study of the impact of the common myna on Australian bird species. Austral Ecology, 39(1): 106-114, doi:10.1111/ Invasive Animals Ltd has taken care to validate the aec.12049. accuracy of the information at the date of publication 6. Grarock K, Lindenmayer DB, Wood JT, [February 2014]. This information has been prepared with care but it is provided “as is”, without warranty of any Tidemann CR (2013). Does human- induced kind, to the extent permitted by law. habitat modification influence the impact of introduced species? A case study on cavity- Produced February 2014 nesting by the introduced common myna IMCS1 Cover image: Peter West

4 www.feral.org.au