If you spend time in the Australian Alps you soon discover they house some pretty unique species of flora and fauna.
The Mountain Pygmy-possum, Burramys parvus, is one such species which makes its home in the boulder fields of the Australian high country. This little possum is considered extra special, being the only marsupial that hibernates under a cover of snow.
However, its populations have been declining due in part to habitat destruction and fragmentation, and predation from invasive feral species. The species is currently listed as endangered under the Federal Environment Protection and Biodiversity Conservation Act 1999.
Adding to these challenges, there has been a dramatic decline in the number of Bogong moths, Agrotis infusa, migrating through the Australian Alps in recent years – a favourite food source for the Mountain Pygmy-possum.
While cesar and their collaborators have successfully helped with the genetic rescue of the Mountain Pygmy-possum at Mount Buller in Victoria, populations in the Australian Alps may face a shortage of food resources due to this decline in the Bogong moth migration.
An epic journey
For thousands of years, Bogong moths have emerged from their pupae in large numbers each spring to begin an annual migration from their lowland breeding grounds – stretching from south-east Queensland down to at least the Riverina region of New South Wales – up to the mountainous landscape of the Australian Alps. Travelling by night, individual Bogong moths can journey over 1000 kilometres in a single migration – an impressive feat for a creature so small.
How these moths manage to successfully navigate over such distances at night is not fully understood, but we do know they can make use of wind systems, have excellent vision and, like tiny biological compasses, they can even sense the earth’s magnetic field.
Sadly for our Mountain Pygmy-possum friends, in the last few years the number of Bogong moths undertaking the migration seems to have suffered an extraordinary decline. While some moths have still been making the long journey to the Australian Alps, their numbers are far below what they once were.
Ecosystem impacts from declining moth numbers
It is likely that the major cause of this dramatic decline are recent droughts – with winter rain across most of NSW in 2017-2019 at record lows. But there are several other factors that could also be playing a role, including underlying warming trends, and changes in agricultural practices.
Research indicates that the Mountain Pygmy-possum may not be the only victim from the Bogong moths’ decline. The moth migration may also be essential for the health of the entire alpine ecosystem. The arrival of billions of moths represents a huge transfer of vital nutrients into the alpine food web, and the moths may also provide other important ecosystem services including nocturnal pollination that we currently know little about.
Decoding the genetics
In 2019, cesar was asked by the Victorian government to assist in addressing key knowledge gaps regarding Bogong moths and their migration to the alps.
In spring 2019, cesar research scientist, Dr Peter Kriesner undertook field collections at several locations in Victoria and NSW using netting and bucket traps to capture the moths at night with a UV light source.
The DNA from a few hundred of the moths that were collected was then extracted and sequenced. Thousands of variable genomic sites in these DNA sequences were analysed, to look for patterns of relatedness among the genotyped moths.
Although there was significant genetic variation overall, we found no consistent differences between moths that were collected from different areas. Moths from the same location appear to be no more closely related to each other than they are to other moths that were collected hundreds of kilometres away, so the Bogong moth population overall appears to be very well mixed – effectively one large panmictic population.
While less is known about the moths’ return migration at the end of summer, our findings indicate that efforts to boost moth numbers at target sites in the alps by locating and protecting particular source populations in lowland areas, are not likely to be practical, and may not even be possible.
On the other hand, if their movements are at least somewhat random the moths should be able to find and colonise new areas, and rebound strongly when environmental conditions improve.
We don’t yet know what impact the recent devastating bushfires, and the huge amount of smoke they emitted, may have had on the Bogong moth population as a whole, but drought-breaking rains in the last few months should offer better prospects to those moths that managed to return to their breeding grounds earlier this year. At least for now, this may be better news for the Mountain Pygmy-possum (and for the entire Australian high country ecosystem).
Looking to the future, these research findings fill an important gap in our understanding of the mysterious Bogong moth biology, and importantly will help to inform recovery programs for the endangered Mountain Pygmy-possum and other alpine species that may depend on the annual Bogong moth migration events.
This project was funded through the Victorian State Government’s Biodiversity On-ground Action – Icon Species Recovery program.
We thank Dean Heinze, Simon Nally, Karen Arthur, Naomi Monk, and Claire Hutton for assistance in obtaining Bogong moth individuals from alpine resorts in Victoria, and from Canberra, ACT.
Additional thanks to Francesca Noakes & Dr Andrew Weeks for their input in the development of this article.