Three years of La Nina-powered wet weather has sparked a rebound in the endangered Bogong moth population, which had plummeted to all-time lows over the past five years.

Tiny but mighty, Australia’s Bogong moths once numbered in their billions. But the drought in New South Wales and Queensland from 2017 to 2019 affected their food plants and triggered a catastrophic population decline of around 99.5 percent, prompting their endangered listing.

Scientists who study the moth believe changes to land use, including the destruction of habitat between 1980 and 2016, caused a slow decline in numbers, and the sudden crash in 2017 was most likely due to severe drought and extreme heat in its breeding grounds

The Bogong moth almost disappeared, but this year its numbers have been higher across its summer alpine range, according to a snapshot published by the Australian Conservation Foundation.

Establishing the presence of these small moths is a Herculean task, particularly because they spend the summer across 20 alpine peaks in geographically remote regions.

In the spring, Bogong moths emerge from holes in the plains in western Victoria, northern NSW and southern Queensland and fly an incredible distance – up to 1000 kilometres – to the Australian alps. They cluster in cool, high-altitude caves during the heat of summer and go into a state of dormancy (known as aestivation).

Bogong moths are a staple food for the endangered mountain pygmy possum but their numbers had a catastrophic decline following drought.Credit:Alex Ellinghausen

At a number of key sites, including Mount Hotham in Victoria, Mount Selwyn and Kiandra in New South Wales and Mount Gingera in the Australian Capital Territory, researchers and observers are “cautiously optimistic” about the number of moths present this year.

Dr Peter Caley, a senior research scientist at CSIRO, has been tracking Bogong moths on Mount Gingera since 2014. This year, the outlook is positive.

“Moth numbers atop Mount Gingera have been increasing over the past month, and are now at levels similar to before the severe 2017-2019 drought,” said Caley. “That it has taken three years of record-breaking rains for the moth numbers to recover [on Mount Gingera at least], speaks to how low the population must have fallen.”

A Bogong moth at Mount Gingera.Credit:ACF

At some Mount Gingera sites this year there were 17,000 moths per square metre, and Caley has estimated there were hundreds of thousands of individual moths on the mountain.

Professor Eric Warrant from Lund University, in Sweden, leads a team of researchers studying the Bogong moths in the Kosciuszko National Park. He was “cautiously optimistic” about moth numbers at Mount Selwyn.

“On two nights in November vast numbers were observed flying overhead and hundreds landed on our illuminated sheets,” he said.

Researchers taking photos of Bogong moths against a survey sheet with ultraviolet light.Credit:ACF

This summer was a pivotal moment for Bogong moths, according to Australian Conservation Foundation nature campaign Darcie Curruthers.

“The 2022 rebound should be a motivation to urgently act on climate change to ensure the species continues to thrive and play its vital role in Australia’s at-risk Alpine ecosystems,” Curruthers said.

First Nations people harvested the Bogong moth annually, a tradition that goes back at least 2000 years. It was a cultural occasion for ceremony and trade for Taungurung, Gunaikurnai and Woiwurrung people, according to Bijil Ba Wudhi Deberra: Bijil and Moths, the first book written for children in Taungurung and English.

Birds, mammals, lizards and frogs all rely on the annual influx of Bogong moths for an influx of summer protein. The critically endangered Mountain Pygmy-possum also relies on the moths to get through its breeding season.

For the past four years, the citizen science website Moth Tracker, established by Zoos Victoria and conservation partners, has been gathering data from Australians who log sightings of Bogong moths to help scientists track their location and migration patterns. This year it has had a record number of verified moth sightings.

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