Australia — home to countless unique animals and ecosystems — is also home to the world's longest fence. It is aimed at a single species, but the dingo fence has transformed the environment in surprising ways.
On most maps of Australia, lines crisscross the continent marking the boundaries of states and territories.
But on the ground, a different border has a much more immediate impact on the human and animal inhabitants of the outback.
The dingo fence starts in the green fields of Queensland's Darling Downs and stretches through New South Wales and South Australia before it abruptly ends on a high cliff's edge above the Great Australian Bight.
It traverses the traditional lands of 23 language groups, over Channel Country, scrub land and deserts.
It is more than 5,600 kilometres long.
If you know what to look for, you can see its effects from space.
"It's longer than the Great Wall of China, but not as well built," says ecologist Mike Letnic.
"Its purpose is to keep dingoes out."
A brief history of dingoes
The ancestors of today's dingoes arrived on the Australian continent between 3,000 and 5,000 years ago — most likely with people from Asia who travelled over the ocean on water craft.
In fact, the very existence of dingoes hints at distant past of human contact between Asia and the Australian continent, long before the dates in our history books.
The nature of those interactions is a mystery. But the new species stayed and became important to life and culture for many Aboriginal peoples.
The new "top dog" was disruptive at first.
Besides humans, dingoes were the largest predator on the land and are suspected of contributing to the thylacine's disappearance from mainland Australia.
However, over millennia, the environment adapted to the dingo just as the dingo adapted to Australia’s deserts, grasslands, forests and beaches. They are now a vital part of the ecosystem.
British colonisation in the 18th century brought a new and tasty target for the now-established dingoes: sheep.
The freshly minted colony rode on the sheep's back and dingoes became an enemy to farmers and graziers.
As farming spread across the country, so did fences.
Rabbit-proof barriers sprung up to stop the spread of that small, hungry, invasive species. Those structures also did a great job of deterring dingoes.
In the early 20th century, sheep graziers proposed an ambitious scheme to keep their flocks safe: the barriers would be joined to create a single, long fence that would keep dingoes out of sheep country altogether.
By the 1950s, around a third of the continent was ringed by the wire fence.
Dingoes were not tolerated inside the fence. To this day, graziers in New South Wales are legally obligated to exterminate dingoes on their lease.
Within the fence and a buffer zone around it, dingoes are routinely shot and poisoned.
The fence varies in height, but much of it reaches 1.7 metres. Although dingoes can scale it, they tend not to. Instead, they trot along the barrier looking for weak spots or holes, a quest that often leads to lethal encounters with poison baits or traps.
Every effort is made to keep dingoes out of sheep grazing land, much of which is arid and remote.
Although a few dingoes remain within its bounds, the fence has achieved its aim.
Dingoes are kept at bay.
Cascading effects
Removing dingoes has changed life inside the fence significantly — and not just for the sheep and their owners.
When it rains, the land on the dingo side of the fence stays greener for longer.
Dingo country is more biodiverse and has more small native mammals. Even the sand dunes are differently shaped on either side of the barrier.
For 20 years, Mike Letnic of the University of New South Wales has been returning to study sites on both sides of the fence, trying to unpick exactly how the absence of dingoes has led to these differences.
"The dingo fence has been a remarkable natural experiment into understanding the effects that apex predators have on ecosystems," he says.
"Dingoes have not been present in great numbers in New South Wales for at least 80 years. And you can see the differences everywhere."
Those differences begin with animals that are comparatively easy to spot: there are "many, many more kangaroos" inside the fence, Professor Letnic says.
That's because, as well as having a taste for sheep, dingoes love to hunt kangaroo. Fewer dingoes means more roos.
When times are good, roo populations boom, but when the rains dry up, they face mass starvation.
With no large four-legged predators to worry about, kangaroos also have time to nibble away at sensitive plants. Inside the fence, this has led to woody shrubs dominating over the diverse array of desert plants that are more quickly gobbled up.
And it's not just kangaroo numbers that are boosted by the absence of dingoes: inside the fence, feral cats and foxes prowl in larger numbers.
These introduced predators played a large role in hunting 29 species of small native mammal to extinction.
Professor Letnic says the problem is particularly bad in desert areas and even worse inside the fence, where there are few dingoes to keep the cats and foxes in check.
"One of the things that makes me really sad when I come out to places like this in the desert is that I know that I've only got the opportunity to see a small fraction of the animals that once lived here."
The small mammal species that have survived the past 200 years are far more common on the dingo side of the fence. These include species like the seed-eating hopping mouse and the mulgara — a tiny but ferocious predator in its own right.
While dingoes may occasionally snack on these creatures, Professor Letnic says their influence on cat and fox numbers makes a bigger difference, improving the environment for small mammals.
And that, in turn, makes a difference to the vegetation — and the sand dunes themselves.
Outside the fence in dingo country, Professor Letnic says, hopping mice eat shrub seeds and seedlings, keeping shrub numbers down.
"Without the shrubs, there is more movement of sand, and we get much more open environments."
Deakin University ecologist Euan Ritchie agrees that removing dingoes has profoundly altered the ecosystem.
"A lot of ecologists have deep concerns about the environmental impact of the fence," Professor Ritchie says.
He describes the fence as "far from a perfect experiment" but says the differences either side of the fence are "relatively convincing evidence that when you lower dingo presence or abundance, there is an impact on the ecosystem".
'There is a war going on'
While the environmental repercussions of the dingo fence are becoming more understood, it does not alter the fact that started it all: it's hard to grow sheep when dingoes are about.
This reality makes many people in farming communities hostile to the predators — and in areas where grazing and dingoes overlap, the landscape is peppered with "dingo trees".
"Dingoes are hung in the tree to let people know that there is a war going on," Professor Letnic says.
"Government agencies [and] farmers often call them wild dogs, and people think they're just kelpies or cattle dogs or Labradors gone wild."
But Professor Letnic routinely clips tissue samples from the hanging animals to get their DNA sequenced.
His verdict? "It's dingoes."
"They call them wild dogs because it's easier, from a public relations perspective, to kill wild dogs … But those domestic animals just don't have what it takes to survive in the wild."
An uncertain future
So, what to do?
Many already-arid areas enclosed by the fence are fast becoming too hot for sheep grazing, says Justine Philip, a research fellow at Birmingham University in the UK. This means much of the fence may soon become redundant.
But at the moment, it is hard to do anything except graze sheep on the dry country inside the fence.
These places are mostly Crown land, Dr Philip explains, and you must be a grazier to take up a lease there. Sheep grazing is one of the only sources of income "because that's the only thing that's supported by the government".
Another income source is maintaining the fence itself. It's collectively funded by graziers, local and state governments, and upkeep costs an estimated $10 million per year.
Dr Philip hopes governments will help communities transition from sheep grazing, especially where climate change is starting to make it impossible.
Where grazing continues, "there are solutions at hand", according to Professor Ritchie.
"We can maintain top predators in the landscape and choose to maintain livestock production as well."
He says a breed of guardian sheep dog called the Maremmano have successfully protected sheep in Queensland.
"And we can have small areas of fencing where you might bring livestock when they are birthing or calving."
Meanwhile, new large-scale fences designed to keep dingoes out of rangelands are being built in Queensland and Western Australia, and Professor Ritchie is deeply concerned about what that means for the environment.
"It's just creating all these barriers to wildlife all over large areas of Australia … It's a pretty horrible vision for the future."
Professor Letnic says it's about striking a balance.
"It's important to remember that dingoes are a pest to livestock producers," he says.
But spaces for dingoes are important too.
"We're coming to realise that dingoes can play an important ecological role.
"I think it's really important that we think about places where we can keep dingoes — and maintain these healthy ecosystems."
Watch Australia's Wild Odyssey on ABC iview.
Credits
- Reporter: Zoe Kean
- Design: Teresa Tan
- Digital editors: Belinda Smith, Jonathan Webb
- Images: Wild Pacific Media, Professor Mike Letnic, National Library of Australia, State Library of NSW, Getty Images
- Video: Wild Pacific Media
- Satellite imagery: Spatial Services, NSW Department of Customer Service and Department of Planning and Environment
