Indian myna driving native bird decline
THE SPREAD OF THE Indian myna, an invasive bird common in cities in the east of Australia, is causing significant declines in species ranging from the crimson rosella and superb fairy-wren, to the willie wagtail and the silvereye, according to a new study.
Although the Indian or common myna (Acridotheres tristis) is on the World Conservation Union (IUCN) list of the 100 worst invasive species, there has been little empirical evidence of the impact of the species on native Australian birds before now.
The new study, published in the journal PLoS One, used survey data from a 29-year period to measure native bird populations in Canberra both before and after the the myna became well established.
Indian myna: negative impact
“We found scientific evidence that the common myna has a negative impact on several native bird species,” says Kate Grarock, lead author and a graduate student at The Australian National University, in Canberra. “Specifically, [on the] the long-term abundance of three hollow-nesting species: the sulphur-crested cockatoo, crimson rosella, laughing kookaburra, and eight small bird species.”
Mynas compete with native species over food, nesting cavities and territory. Both sulphur-crested cockatoos and crimson rosellas were increasing in abundance In Canberra before the Indian myna became well established in 1989. However, the study found that after 1989 the growth rate of the crimson rosella fell by about 60 per cent, and the sulphur-crested cockatoo by about 20 per cent.
Kate’s study also showed adverse impacts on other native species such as striated pardalote, grey fantail, magpie-lark and common blackbird.
Native to a large area of the Middle East, India and Asia, the myna was introduced in Australia in 1862, to control insects in Melbourne’s market gardens. Their numbers have exploded in Canberra, increasing from the 110 birds deliberately released between 1968-1971 to more than 90,000 in 2006 – although humane trapping has since reduced their numbers by about 42,000.
According to Kate, previous studies focused mainly on observing the competition for nesting sites between the myna and native species. “However, the next step was to show that this competition results in reductions in the abundance of native species,” she says.
Result of many years of bird surveys
The data, collected by the Canberra Ornithologists Group Garden Bird Survey, provides a rare opportunity for studying the long-term impacts of an invasive species, comments Dr Susan Campbell from the Department of Agriculture and Food, Western Australia.
“Common mynas are very good at living in conjunction with humans, which means they become a pain around houses,” Susan says. “Because of this [ability], their numbers have exploded in urban and semi-urban areas on the eastern coast, although they are yet to establish in Western Australia.”
Susan adds that control of a species becomes much more difficult once it has become well established in an environment. However, knowing the impact of invasive species, such as the myna, on natives may lead to stronger campaigns to prevent their establishment.
“There is a need for control of these birds before their population numbers explode [and] if we understood better their impact on native birds then we could make a much stronger argument for their control,” she says.
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