Debate has raged for more than a decade about
the damage caused by swelling myna populations, both in Australia and other
countries around the world, leading the pesky bird to be rated No. 3 on the
IUCN's list of the worst invasive species. Now a team of Australian researchers
has come up with what is thought to be the world's first clear proof that mynas
do indeed have a negative impact on native bird numbers. In a long running
study, Kate Grarock and her colleagues of the ARC Centre of Excellence for
Environmental Decisions (CEED) and Australian National University investigated
20 birds species round the national capital, Canberra, analysing ornithological
records of bird abundance collected by the Canberra Ornithologists Group (COG).
COG established the Canberra Garden Bird Survey (GBS) in 1981 in which
volunteers surveyed birds in and around the city. Observers survey an area of
3.1 hectares every fortnight for a 120-minute period. A total of 74 492 surveys
was undertaken in Canberra over 29 years "We found a negative relationship
between the establishment of the Common Myna and the long-term abundance of
three Australian cavity-nesting species and eight small bird species," Ms
Grarock says. The birds most affected by mynas were cavity nesters like the
Sulphur-crested Cockatoo, Crimson Rosella, Laughing Kookaburra, and small birds
such as the Superb Fairy-Wren, Striated Pardalote, Rufous Whistler, Willie
Wagtail, Grey Fantail, Magpie-lark, House Sparrow, Silvereye and Common
Blackbird. Larger birds like magpies, wattlebirds, galahs, ravens and
currawongs appeared unaffected. "To the best of our knowledge, this
finding has never previously been demonstrated at the population level,"
she adds. "It is particularly difficult to track the impact of an invasive
species on native wildlife when it isn't an actual predator, as this can take
place subtly and over a long time and can vary season by season," she
says. "Also you need to know whether it is the invader that is causing the
damage – or whether it is simply due to habitat change, such as cities
expanding."
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