So far, 18 wild parrots have returned with an even nine males and nine females. There are still several weeks remaining for others to complete the journey back from the mainland.

Orange-bellied parrot expert Mark Holdsworth said the result had surpassed their expectations.

"We were predicting only 15 would show up, based on previous averages. We'd like a lot more, that's for sure, but 18 is tracking much better than anticipated," he said.

"Numbers from the last few years have been disappointing, but this season is so far as good as we could hope for.

"If we get into the 20s, that would be extraordinary."

The result means there will be 20 pairs to attempt to breed at Melaleuca with their numbers topped up with captive-bred birds.

Of the 18 that have returned, 10 were wild-born, three were captive-bred that were released as juveniles this year, two were released as juveniles last year, and two were released in previous spring releases.

Another was a wild-born bird that had previously been head-started and released.

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Their exact migratory route remains a mystery, however it is believed they fly up the West Coast of Tasmania, cross the Bass Strait and settle in coastal Victoria or South Australia before returning. Some could even remain in Tasmania as a response to climatic conditions.

Making the migration is a necessary risk in itself, but surviving the winter remains the greatest challenge for orange-bellied parrots.

There are fewer than 30 left in the wild.

Mr Holdsworth said recent winter survival rates had been poor, but this season appeared to be an exception.

"The last couple of years, the survival over winter has been very poor, as low as 12-15 per cent surviving the winter," he said.

"It's possible some have stayed somewhere in Tasmania over winter, which could be driven by a changing climate. But none of our volunteers had been able to find them.

"This year the survival rate has increased."