The gang-gang cockatoo is in decline.
According to the Blue Mountains Bird Observer group (BMBO), the reporting rate of the once common gang-gang across all areas of the Blue Mountains in the past two decades has dropped by up to 70 per cent, with some believing they are being chased out of their territory by aggressive sulphur-crested cockatoos and rainbow lorikeets.
And it's a trend being repeated along the whole east coast, according to the State of Australia's Birds report, released last week. The report is part of a broader look at the health of birds and their environments, covering 15 years of data.
A BirdLife Australia spokesman, Glenn Ehmke, said in the last seven years in particular there had been a "significant decrease" in the entire east coast regions of the small grey cockatoo, which is found across the ranges and coast of south-eastern Australia from the Victorian border to the Hunter Valley of NSW.
Mark Ley, president of BMBO, said members of the group started to notice a decline in gang-gang numbers about 15 years ago.
"BMBO has been collecting data since the early 1990s and this species was commonly reported ... with flocks of up to 50 individuals seen in some areas. We never see anything like that anymore with the rare sightings usually consisting of less than 10."
Mr Ley said there were a number of possible causes, including competition from other birds, but "without some dedicated scientific research it is hard to identify the exact cause".
Many of BMBO's 130 members consider that competition for nesting hollows from sulphur-crested cockatoos and rainbow lorikeets had been the primary cause of the decline.
"I recently observed about 10 sulphur-crested cockies harassing a small flock of gang-gangs at Blackheath Rhododendron Gardens and actively chasing them from the area," he said.
Bird tour operator Carol Probets said BMBO records have "confirmed what we've been thinking for a few years now".
"My entire business is birdwatching, or birding, tours. Gang-gang cockatoos are always a favourite amongst clients and definitely one of the top 10 desired species to see. They are charismatic, approachable and photogenic, keenly sought by birders who visit this area. But they're definitely much harder to find than they were 20 years ago." Ms Probets, of www.bmbirding.com.au, also believes that the bird is being forced out of breeding areas, adding they have plenty to feed on.
"Competition for nest hollows seems a likely explanation when you consider the huge increase in sulphur-crested cockatoos. They are adaptable, aggressive and larger than gang-gangs and would certainly be capable of winning any battle for a suitable nest hollow."
Ms Probets said "long-lived birds such as gang-gangs might fail to breed for many years before it's noticed. For this reason sightings of juvenile birds are especially valuable. I can't remember the last time I saw a recently fledged Gang-gang".
Details on BMBO membership and walks to www.bmbo.org.au.