Australia's orange-bellied parrot spends winter fossicking in the coastal salt marshes of Victoria and South Australia before returning from late September to Melaleuca in the Southwest National Park.

Wildlife biologist Mark Holdsworth said 35 parrots made the journey north earlier this year - as of Friday night, 10 had returned. All were males.

Mr Holdsworth - who coordinated orange-bellied parrot recovery efforts for 25 years - said the first wave of arrivals were older, more experienced birds. Disappointed that none of the older females appeared to

have successfully made the crossing, the survival of the species, he

said, now depended on at least some of the 12 younger females being among the next wave to cross Bass Strait.

"It's an anxious time for everyone right now, because the survival of the species depends on females turning up," he said.

"If not, they'll be functionally extinct."

Mr Holdsworth said a normal survival rate would see about half the birds die over winter - either through starvation, predation, severe weather or old age.

"That means, based on long-term averages, we expect six or four females to turn up," he said.

"But, of course, that depends on how they fared over winter."

The good news for the orange-bellied parrot is that, if that average holds true this season, it would amount to twice as many females as survived last year's migration.

Of the 45 parrots that had migrated north to the mainland the previous autumn, only 14 returned to the island state - and just three of those were female.

But with such a small population, just one catastrophe could spell the end of the orange-bellied parrot's days of living wild, Mr Holdsworth said.

"In a healthy population of hundreds of thousands, the loss of one individual is neither here nor there," he said.

"But we expect the total population this year to be no more than 20 - if we are lucky - so the loss of just one bird can be disastrous."

Concerted efforts to prevent the birds from disappearing over several years have produced a stable population of about 350 captive birds.

Tasmania's Department of Primary Industries, Parks, Water and Environment said it would release up to 24 of the wild population in Melaleuca to bolster the bird's population this breeding season.

But Mr Holdsworth said the captive-bred birds were less fertile and less likely to survive in the wild.

"Anything that produces some nestlings is positive ??? but captive birds have a much lower survival rate," he said.

"We expect about a 50 to 60 per cent of wild birds will survive from one year to the next, sometimes as high as 90 per cent.

"With captive birds, we'd be lucky to get 10 per cent."

Mr Holdsworth is anxious to see if any of the dozen female hatchlings from last year can survive their first migration to Tasmania. In the meantime he is celebrating the little victories. Like

the arrival of a 10-year-old parrot - general life

expectancy is less than four - and sightings on the mainland of a young female, Matilda, the only chick to survive recent efforts to translocate captive-bred birds to wild nests.

"You go from disappointment to moments of elation, occasionally," he said.

"We're holding our breath to see if Matilda will turn up; that would be a great moment if she does."

Any surviving younger birds are expected to arrive at Melaleuca over the next three weeks - none are likely after November.