Missing the Bogong moth

Missing the Bogong moth

There are two things that are very important in the Australian alpine regions. One is sunshine, and the second is Bogong moths. 

That’s how important these moths are. 

They’re an amazing creature, famous for their yearly migration over vast distances – from the grasslands of southern Queensland, western and northwestern NSW and western Victoria to South Australia, all the way to the alpine regions of NSW and Victoria around the end of September. Some of them navigate their way over 1000km. Once in the alps, they seek shelter in high caves and rock crevices, usually at elevations above 1800 metres. They line the walls of these cool alpine caves and aestivate (a summer “hibernation”) over the summer months, returning to their breeding grounds at the start of autumn, where they mate, lay eggs and die. The moths hatch the following spring and the cycle continues.

Agrotis infusa
Bogong Moth (Agrotis infusa). Credit: WikiMedia

They’re a major food source in the mountains for numerous mammals, insects, birds, fish, reptiles – there are even two nematodes in the mountains which feed exclusively on Bogong moths. Most of the wildlife up there is feeding on them in one way or another.

Last year I was involved in a meeting with the IUCN, the International Union for Conservation of Nature, to make a case to have Bogong moths on their red list of endangered species. I remember they said, “You’re talking about a crash in their numbers. What would you call a crash? Is it 50%? Maybe 60%?” I did a calculation and worked out that the crash in numbers in 2017/18 was 99.5%.

I didn’t set out to study Bogong moths in particular. I came up from South Australia in the 1970s to study applied science at what was then the Canberra College of Advanced Education. From Canberra, we could easily drive up to Mount Ginini in the Brindabella Ranges. When I first went up there with friends, they gave me these cross-country skis. I put them on and said, “What do I do now?” And they said, “Just keep shuffling.” And that was the beginning of my love affair with the Australian alps. 

They’re an amazing creature, famous for their yearly migration over vast distances

Will Osborne and I started together in the same year, and we would head up there skiing or walking at every opportunity. As I’ve done ever since, I’d always carry a notebook to record everything of interest. He was doing the same. By the time we had both finished our PhDs in zoology at ANU, we realised we had enough between us to put together a book on the wildlife of the Australian snow country. It’s in its second edition.

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We weren’t doing any specific work with Bogong moths, but we were recording our observations whether it was a good year, average or a bad year for them. Just writing this stuff down has given us records going back to the 1970s. 

The only other scientific work that had been done on Bogong moths was by Ian Common in the early 1950s, and by Josephine Flood, who described the importance of the Bogong moth to the Aboriginal people in a book called The Moth-hunters

Just writing this stuff down has given us records going back to the 1970s. 

We finished our PhDs, and then I did about eight years work with the Antarctic Division while we put our book out. It was quite coincidental that as I was finishing up there I was working in a temporary role on long-footed potoroos in Victoria when a job came up back at Kosciuszko, and so I applied and got an interview. At the end, they asked me if there was anything else of interest that I would like to show them, and so I handed across our book – and yes, I got the job.

That was 25 years ago. I continued looking at whether Bogong moths were having a good year or a bad year. Then, in the summer of 2017-2018, the population just crashed.

We knew that from the 1950s to about 1980 the population went up and down a little bit, but there wasn’t huge variation. But from 1980 onwards there started to be a number of bad years, more medium years and fewer good years. We put it down to climate changes, as even back then climate change was starting to have an impact elsewhere in the world. The moths that had been coming up to the mountain ranges around Canberra started moving away to higher elevations, and that seemed to fit the story. So there was patchiness – and then suddenly the population just crashed.

In the summer of 2017-2018, the population just crashed.

The drought must have been a factor in their sudden decline, but there has been no recovery since. Last summer was worse than ever in the mountain ranges around Canberra. 

Finding out how many Bogong moths there were in the mountains was a bit of a challenge. I went out to western NSW and found Bogong moths in their holes in the ground – we shifted quite a few tonnes of soil doing survey work. But we were able to work out that there were 7.9 billion Bogong moths heading for the alpine regions in a good year. Of these, only about 3.8 billion made it. And then the local animals knocked off another half of that. So that left only about 2.1 billion, and that lot then had to turn around and fly back where they came from at the end of the summer. 

There’s one glimmer of hope.

There’s a cave up there on Mt Kosciuszko at an altitude of 2100 metres where they aestivate – a certain percentage of the Bogong moths fly around for about an hour before dark and then go back into their caves. We were working there and on the Ramsheads last summer. On the Ramsheads cave we only saw 12 Bogong moths. There should have been millions flying around. 

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There’s one glimmer of hope. Bogong moths have the potential for three overlapping generations when there is access to enough larval food plants, and it’s the spring generation that flies up into the mountains. With all the rain we’ve had, there have been some reports of Bogong moths appearing over the last month or so out near the South Australian border. Maybe their numbers will build up enough, and they may actually be back in the way they should be. We’re hopeful for a better year this year.

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