There has been little good to say about the recent history of the critically endangered orange-bellied parrot. Numbers of the small migratory bird, which makes a return trip from Tasmania’s south-west wilderness to the mainland’s coastal scrubland each year, have fallen so sharply scientists consider it at risk of extinction within five years.

Just 23 birds arrived at the species’ breeding site at Melaleuca, deep in the Tasmanian World Heritage Wilderness Area, last spring.

But six months on there are tentative positive signs, with the number of birds heading north for the winter reaching 118, the first time the flock has topped 100 in more than a decade.

Dr Shannon Troy, a wildlife biologist with the Tasmanian Department of Primary Industries, Parks, Water and Environment, says the population has swelled in three ways, some of them the result of work undertaken by a national recovery team.

The group of migrating birds arriving in Melaleuca for the breeding season were met by a further 34 adult birds released from captivity, including some from a new breeding facility at Five Mile Beach, near Hobart airport. The adults from different backgrounds together produced 37 fledglings, and were joined by another 49 captive-bred juveniles.

Not every bird survived the warmer months until the parrots headed north between February and April, and the rigours of long-haul travel means less than half those that leave are likely to return.

Troy says a good scenario would be 40-to-50 parrots turning up in Melaleuca from September for the next round of breeding. While still a perilously low number, it would be more than double the wild population of a couple of years ago, when it fell to 17.

“There’s years when things are not good and it really is disheartening so you decide to celebrate the wins,” Troy says.

Wildlife biologist Shannon Troy monitoring orange-bellied parrots at Melaleuca, Tasmania. Photograph: Department of Primary Industries, Parks, Water and Environment.

“It is an amazing feeling to have had over 100 birds migrate together, but at the same time it’s one step. The real change we need to see is the number of birds in spring. That’s census time.”

One of the challenges in attempting to build a population from such a low base is its limited genetic diversity. In the spring of 2017, there were just three mature females remaining in the wild. That grew to 13 before last breeding season, but the reduced gene pool increases the risk of disease having a species-wide impact as the remaining birds have similar patterns of immunity.

Troy says there is precedent for rebuilding a species from numbers this small. She gives the example of the black robin in New Zealand, which was reduced to one mature female in the wild before numbers rebounded into the hundreds.

“There are plenty of populations of bird around the world where genetic diversity is low, but a species has still been able to recover,” she says. “It is definitely a concern, but not necessarily a showstopper.”

Dejan Stojanovic, leader of Australian National University’s difficult birds research group, says the good breeding season is great news – obviously enough, there need to be more parrots in the wild for it to recover – but also stresses the greatest threat to the species is survival during the winter migration months.

“Hopefully more birds leaving Tasmania corresponds to more survivors returning next spring to breed,” he says. “The big test for all these parrots is still to come.”