“99.5% drop”: what caused the bogong butterfly disaster in Australia? | The threatened species


IIt is conventional wisdom among wildlife lovers that the more charismatic an animal, the higher its profile. Cute and cuddly species – fluffy mammals and colorful birds – grab public attention, while less attractive animals scramble in the dark. In eastern Australia, a famous insect is an exception to this rule.

In appearance, the bogong butterfly is perfectly average: it does not stand out from all other anonymous moths of the moth by size or color. It’s small, but not remarkably small, and brown, but a dull mouse brown. You wouldn’t look at it twice, but on the one hand: the absolute number in which it is gathered.

When I was growing up in Canberra, carpets of bogongs lined the walls of Parliament apparently every year. Images of them swept from white walls by the thousands live in my mind. My mother, who worked in Parliament, remembers bogongs floating all over the green seats in the House of Representatives.

They were so common and so reliable that the City Environmental Center Journal, where I briefly volunteered while studying at Australian National University, was named after them.

Most importantly, bogongs are a part of this continent’s deep history: in February, remnants of cooked bogongs were found on 2,000-year-old grindstones in a cave in the Australian Alps, in the land of Gunaikurnai, considered as the oldest archaeological evidence in the world. the world of insects as a source of food.

Each year, moths, which weigh only a third of a gram, fly up to 1,000 km from southern Queensland to the Victoria Mountains, including Mount Bogong, the state’s highest peak.

But these amazing insects are in trouble. In 2019 rely on one hand.

A navigation miracle

A bogong’s first migration is south: adult butterflies emerge from the ground in Queensland where they have lived as caterpillars during the colder months of the year, and then as the season turns they fly. south to the Victorian mountains, where they spend the summer sheltered in caves and crevices, not eating but relying on fat stores. Then, before the snow arrives, they return to Queensland to reproduce and create a new generation of caterpillars which will continue the cycle the following year.

A butterfly bogong flies into Rafael Nadal during the 2017 Australian Open. Photograph: Lukas Coch / AAP

Ken Green, a professor at Australian National University and expert on moths, says they are able to navigate their long migrations in several different ways, with each butterfly following the route for the first time in its short life. Perhaps most remarkably, they can detect the earth’s magnetic fields – but it saps energy, so once they get their bearings “they turn off their magnetic sensors,” Green says.

If the night sky is clear, they can navigate by the stars instead.

“The Milky Way is brighter in the south than it is in the north, so when they migrate in the spring, they just head for the brightest piece that brings them south, and when they turn to go home, they pass the northern end of the Milky Way, “says Green. And if the stars aren’t visible,” they can choose where the moon is even when it’s seven degrees below the horizon. “.

The long migration has given rise to many theories about the causes of the decline in the number of moths, which has been so dramatic that it even surprised the International Union for the Conservation of Nature (IUCN).

“When we had the meeting with IUCN,” says Green, “they said, so you said there was a collapse in the numbers, would it be 60%, 40%, 20% ? I said ‘No, based on our numbers we’re talking about a 99.5% drop.’

Green’s research found that clearing land for crops in the Murray-Darling Basin, the primary winter breeding ground for moths, has removed about a quarter of a billion specimens each year from the mountains above pre-levels. -europeans. He says changing farming practices likely led to part of the decline in butterfly numbers seen between 1980 and 2016, but the sudden crash in 2017 was most likely due to severe drought in the breeding grounds.

Bogong butterflies at Canberra Houses of Parliament on their annual migration from Queensland to the Snowy Mountains in 2007.
Bogong butterflies at Canberra Houses of Parliament on their annual migration from Queensland to the Snowy Mountains in 2007. Photograph: Alan Porritt / AAP

Marissa Parrott of Zoos Victoria adds other potential factors, including increased use of pesticides such as neonicotinoids in Australia (some of which are banned in other countries), increased light pollution, which disrupts migration of butterflies, destruction of habitat and flowering plants on their migratory routes and an increasingly hot and drier climate.

Cascading Effects

The loss of any species is a tragedy in itself, but the rapid disappearance of bogong butterflies has much wider effects. Like many insects, bogongs are at the bottom of the food chain. They are a major food source for another critically endangered animal, the mountain pygmy possum, and a boon to the entire Alpine ecosystem.

Moths provide a necessary feast for mountain pygmy possums that wake up from hibernation, Parrott says, and are also a key food source for “birds, other mammals … reptiles and frogs. , many of which are endangered in alpine regions “.

“Even other invertebrates, such as ants and spiders, are seen feasting on moths. The nutrients left behind each year by moths are also important for soil and alpine plants.

There are even two species of parasitic nematodes that depend entirely on bogong butterflies for their survival, says Green.

Bogongs are a major food source for another critically endangered animal, the mountain pygmy opossum.
Bogongs are a major food source for another critically endangered animal, the mountain pygmy opossum. Photograph: Bloomberg / Getty Images

Moths are important not only as a food source, but also because they feed on themselves. Bogongs are nectar eaters, which makes them potentially important pollinators. Parrott warns that we don’t yet know what effect the sudden loss of millions and millions of pollinating butterflies could have on plants along their migratory route.

“Considering the large number of moths and how many flowers they would visit, this should be of great concern,” she said.

Due to the insect’s high reproductive rate, the number of bogongs may recover – each female can lay up to 2,000 eggs. But butterflies can’t do it all on their own.

Parrott says that “additional support for their habitat and less destructive farming practices are needed.”

“Everyone can help by not using insecticides, turning off outdoor lights unnecessary for moths, and planting native flowers that support moths such as correa, eucalyptus, tea tree, grevillea. “

And anyone along the bogong butterfly migration route can help scientists track them by recording their sightings on Zoos Victoria’s Moth Tracker. If we see bogongs by the millions again, knowing how close they are to extinction, perhaps we could have a new appreciation for these nondescript, spectacular little brown animals.


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