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ScienceWise - Mar/Apr 2009

Rats of the sky?

Article Illustration
Kate Grarock is building nest boxes and removing pest birds from Canberra’s suburbs to measure the impact of Indian mynas
Article Illustration
Two hundred and ten nest boxes were constructed for Kate’s experiment. That’s a lot of ply board and several bruised fingers!
Article Illustration
Myna eggs and a baby found in one of the next boxes.

Just how damaging are Indian Myna birds to the Australian environment?

Indian mynas are an introduced species that many people love to loathe. In a recent ABC poll, they were voted “the Most Significant Pest/Problem” in Australia. They’ve also been placed on the IUCN’s world’s 100 worst invasive species list. Some people even call them the “rats of the sky.” But just how damaging are these pests, and what can we do about them? Kate Grarock at the Fenner School of the Environment and Society is undertaking the research to come up with the answers.

The Indian myna (Acridotheres tristis) is native to India and southern Asia. In the 19th Century mynas were introduced to many countries as a form of biological control for insect pests in agricultural areas, and they have proved amazingly adaptable. In 1863, 42 birds were released in Melbourne, and then later mynas were released in Sydney and north Queensland. Now they’re common throughout the eastern states, often in high densities in urban areas.
They were released in Canberra in 1968. In 20 years they were in half of Canberra’s suburbs. By the year 2000 they were judged to be the most common feral bird in the ACT. Today they are in every suburb, sometimes in densities over 100 birds per square kilometers, and numbers are still increasing in some areas.

“Many people hate Indian mynas because they’re so visible in our suburbs and backyards,” says Kate Grarock. “They prey on native birds, take over precious tree hollows, steal food from our tables, and create noise and mess when they come together in roost trees – often in their hundreds. They’ve got a high profile but most of the evidence against the Indian myna is anecdotal. Some people question whether they really are having an impact on native species.”
But the lack of hard evidence hasn’t stopped people hating them and getting together to try and stop them. There are several anti-myna groups around Australia and in the ACT there’s the Canberra Indian Myna Action Group (CIMAG) with several hundred members. CIMAG has trapped and removed almost 20,000 mynas but some have questioned whether this is actually achieves anything.

“So here are some important issues that need attention: How many mynas do you need to remove to make a difference? How quickly do mynas recover from removal? Does removal of myanas have a positive effect on native species?”
To answer these questions Kate is conducting a major myna bird removal experiment across Canberra as part of her PhD research. With the help of CIMAG she is removing high numbers of mynas in five suburbs, medium numbers in another five, and comparing this with five control suburbs in which none are removed.

Each of the 15 suburbs will be monitored by transect counts of all bird species present, and through the establishment of over 200 nesting boxes (to monitor nesting success of both natives and mynas). This will be one of the largest myna removal experiments ever attempted in Australia.

“By undertaking this experiment at this scale and with this level of replication we’re hoping we can clearly and scientifically demonstrate the impact mynas are having on native species,” Kate explains. “To date, the impact mynas have on our natives is largely unqualified. We know it occurs, but not to what extent and which native species are most impacted.”

“We’re also hoping to establish the level of myna removal required to meaningfully reduce overall numbers. Is it feasible to just concentrate on trapping one suburb at a time or do you need to focus on a much larger area?”
“We’re also hoping to learn how Indian mynas respond when you start removing them from the area. An understanding of how mynas adapt to a reduction in numbers may hold the key to ensuring that reductions are long lasting. It’s hypothesised, for example, that mynas will rear more chicks in removal areas, than those in non-removal areas.”
To assist in monitoring the impacts of the removal experiment, Kate has built and deployed over 200 wooden nest boxes through the treatment suburbs. The nest boxes provide preferred habitat to a number of different native species and are also sought after as homes by the Indian mynas.

“The nest boxes are easy to locate and check on a regular basis,” says Kate. “We’re expecting to find them used by quite a few mynas in the control suburbs but it’ll be interesting to see what’s using them in the medium- and high-myna bird removal sites.”

It’s still too early to say whether the removal treatments have worked and if removal has led to an increase in native species. However, whatever results turn up in the coming year, this study will give us a much improved understanding of the real impact of myna birds. And we’ll be better placed to effectively manage them in future.

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