Bogong’s back: La Niña rains help moth numbers recover from near extinction

The bogong moth population has started to bounce back after nearing extinction but the insect's future remains fragile, a new report has found.

"It's looking really positive but it's still too early to be confident yet," said Marissa Parrott, a reproductive biologist at Zoos Victoria.

"We know that numbers can fluctuate between years and we know they're still low compared to what they should be."

As of 16 December, there had been 269 sightings of bogong moths on Zoos Victoria's Moth Tracker, which encourages Australians to submit sightings.

Bogong moths once had a population of almost 4 billion migrating to the alpine region to escape the summer heat - they were so common, the swarm seemed to "block out the moon".

But in 2017 after relentless drought, the population declined by about 99.5%. And last year, the moth was listed as endangered on the global red list of threatened species.

Atop Mount Gingera, in the ACT's alpine region, the number of moths had returned to similar levels before the most recent drought, Peter Caley, a senior research scientist at the CSIRO, said in the report.

"That it has taken three years of record-breaking rains for the moth numbers to recover to pre-drought levels [on Mount Gingera at least], speaks to how low the population must have fallen," he said.

At Mount Selwyn in Victoria, Prof Eric Warrant, who studies the bogong moths at Lund University in Sweden, was "cautiously optimistic" about the moth numbers, he wrote in the report. Warrant leads a team of researchers that collect data on the moths through light traps.

"The numbers are better than they've been for quite some time and on two nights in November vast numbers were observed flying overhead and hundreds landed on our illuminated sheets," he said.

As well as being culturally significant for traditional owners, the moth is vital to the healthy functioning of the ecosystem it resides in. When the population plummeted, the mountain pygmy possums, which rely on the moth as a food source, suffered significantly.

In 2018-19, more than 50% of female mountain pygmy possums among the monitored Victorian population lost their entire litter, Parrott said. In the worst-affected areas it was 95%.

Since moth populations have increased, Parrott said, the population of mountain pygmy possums is "much lower than it should be but we are getting reports from the field that breeding has improved".

The recovery of the bogong moth is tenuous, with threats to its survival remaining.

"It's a real concern that as we head into a warming climate that we are going to have those droughts that could keep knocking moths down to really scary levels again," Parrott said.

Caley said he is confident the recent delugewill keep the moth numbers healthy for the next few years but more understanding is needed on what drives their populations.

The bogong moth is not yet listed as an endangered species in Australia and Parrott said it's important action is taken now to recover the species.

As for what the public can do to help, Parrott advised people to "turn off unnecessary outdoor lights, don't use insecticides, plant native plants to support moth migration up to the alps and back to their breeding grounds again in autumn, and keep using things like Moth Tracker to help us gather data".