September 18, 2012
It is mid-morning in Perth’s foothills, and I am standing in a cage full of large black birds.
One of them is perched on my shoulder, trying to nibble my camera as I struggle to focus on a flurry of black and scarlet feathers surrounding the other man in the cage. Phil Digney manages the black cockatoo rehabilitation centre Kaarakin. He has another of the rescued Forest Red-tailed black cockatoos on his head, feeding its full-grown daughter perched on his shoulder. The bird on my shoulder has a raucous cry, loud enough to hurt my ears as I concentrate on what Mr Digney has to say.
Many of the aviary’s residents have arrived at the sanctuary as rescued chicks, after losing their parents to road accidents and other mishaps, and most have been hand-raised.
Mr Digney (pictured) says more Forest Red-tailed black cockatoos are foraging for food down on what hills people call “the flats” (the Swan coastal plain), where the species was almost unknown just a few years ago. Almost a third of the 290 injured or orphaned black cockatoos that have arrived at Kaarakin since January 2011 have been Red-tails.
WHY DID THEY COME?
WA Museum’s bird curator says the cockatoos seem to be attracted to the seeds of the exotic Cape Lilac tree because their staple diet, the native red gum or Marri nut, is suffering the effects of climate change and a disease called Marri canker.
“We first noticed birds feeding on Cape Lilac up in the Roleystone area about 14 years ago,” says Ron Johnstone, who has studied Red-tails for much of his career. “That slowly expanded so that you had birds coming down to the Armadale Reptile Centre, coming down to Kelmscott on the coastal plain, finding Cape Lilacs, feeding on them and returning back to the escarpment to roost. That just progressed and eventually the birds were moving from Kelmscott through to Gosnells along the Canning River, right out to places like Thornlie, through to South Perth and we were able to follow birds that were leaving the Victoria Dam up in the hills and getting right across to places like Bentley. It’s become a fairly regular occurrence … right though to Freo and right up … to places like Middle Swan and Carine.
“So it’s been a fairly recent change in foraging ecology for a bird that was essentially very localised. For the first five or six years of our study … they were hardly moving more than a kilometre from their region of origin. Wandering from the escarpment right out to Freo and then back again each day is a huge move and not very energy-efficient … it’s obviously had an impact on their breeding biology.”
Mr Johnstone tells me the birds in the wild require large tree hollows to build their nests. In the wild, a Marri or Tuart tree must be at least 200 years old to provide a big enough hollow. There are very few such trees in Perth, and many of the remaining hollows are occupied by feral bees.
NEW NESTING HOLLOWS
Murdoch University scientists placed 11 artificial nesting tubes around the campus bushland last year, and a pair of Red-tails chose to nest in one of them, producing a chick. Murdoch Environmental Rescue Group spokesman Neil Goldsborough says last year’s success is about to be repeated.
“There’s a pair that’s breeding in one of the nest tubes and we’re actually going to be banding [the chick],” he says.
The group is erecting another 11 tubes, in the hope that it will attract more of the fickle Red-tails to breed closer to their new foraging grounds.
Mr Johnstone says the Red-tails, which live for up to 50 years, have never been prolific breeders in the wild.
“We have some years where in all the nests that we’re monitoring we haven’t had a single pair actually raise a chick successfully. So we do have some concern over the conservation of this population. They only breed about every three years and they require deep, large hollows where you’ve got a fairly good floor space for the female to incubate and brood the chick.”
Back at Kaarakin, Mr Digney is inspecting another cage with a collection of six natural hollows salvaged from ancient forest trees. Six pairs of wild Red-tails, whose injuries make them unfit for release, are also in the large metal cage.
“They are all wild birds and this is our true first breed-for-release aviary,” he says. “They will just be permanent rehab birds that we’ll still use [to] augment the population in the wild for breeding. We don’t know how well that will go, but through soft release, a period where they’ve got access to food and freedom in the wild as well, we think it will go okay.”
Photos: Geoff Vivian