Introduced Corellas were first reported as causing a nuisance in Bunbury in August, 2010, when a flock of between 500 and 1000 birds were roosting in trees around Horseshoe Lake.
As they have no natural predators besides humans, and as access to food and water is unrestricted, numbers have been increasing over time and are expected to continue increasing. It is inevitable that the adverse impacts they cause will also increase as their population expands. As well as causing nuisance through excess noise and fouling, introduced Corellas also cause damage to playing surfaces such as grass fields, Astroturf and bitumen, and to other infrastructure such as aerials and wiring.
They also cause significant damage to their roosting trees through continual pruning.
A recent survey by the Western Australian Local Government Association (WALGA) showed that introduced Corellas are considered to be a problem by ten local government authorities, six of which were in the Perth metropolitan area and four of which are in the South West.
Introduced Corellas are also immediate and significant competitors with local native bird species that are hollow-nesters, such as parrots, native cockatoos, owls, raptors, some duck species and all three species of listed black cockatoo; Carnaby’s Cockatoo (Calyptorynchus latirostris), Baudin’s Cockatoo (Calyptorynchus baudinii) and Forest Red-Tailed Cockatoo (Calyptorynchus banksii naso).
This impact is likely to increase as the number of mature trees available for nesting declines as a result of clearing for industrial development, agriculture and housing. Introduced corellas will also present a threat to populations of the endemic Western Corella, including the endangered Muirs Corella, if they continue to increase and expand their range (DEC, 2009b).
Hybridising in the wild, introduced corellas are also compromising genetic purity, and threatening the longterm viability of populations of native corellas and galahs. Known hybridisations include Little Corella x Eastern Long-Billed Corella, Eastern Long-Billed Corella x Galah and Little Corella x Sulphur Crest Cockatoo (DEC 2009b).
The most effective method for controlling the Corella’s is to attract them to an area over a period of time, net them and then exterminate them. This is the method currently being utilised by Shires in the South West where Corella’s have been causing the most damage.