World’s longest fence affecting the development of kangaroos

Kangaroos spring up faster when they’re living with their predators.

Stretching over 5,000 kilometres from Queensland to South Australia, the dingo fence is designed to protect southeastern Australia’s sheep farms from predatory dingoes. However, it’s also a barrier to many other forms of wildlife, including kangaroos.

New research has revealed that young kangaroos outside the fence are much larger than those of the same age inside the fence. As dingoes tend to target smaller kangaroos, this likely makes them less of a target.

The team behind the study have called for more research into the effects of the fence, amid calls for it to be taken down.

Co-author Dr Vera Weisbecker says, ‘The fence is a unique Australian megastructure, and a huge predator-prey experiment.’

‘Examining how the fence modifies our native wildlife is important in the continuing debate over the efficiency and merits of the dingo-proof fence, not only relative to the dingo itself, but also to the invasive species such as rabbits that the dingo eats.’

The findings of the study were published in the Journal of Mammalogy. 

Australia’s giant fences

Australia is home to some of the longest fences in the world, and have their origins at the turn of the twentieth century. At the time, concerns over invasive rabbits damaging crops and affecting native species saw some regions try to fence out the problem.

This resulted in three large fences built across sections of the country – Western Australia’s state barrier fence, Queensland’s Darling Downs–Moreton Rabbit Board fence, and what is now known as the dingo fence.

While this latter fence was relatively unsuccessful at keeping rabbits out, it was able to keep out larger animals. Support from farmers and the government meant that the rabbit fence was upgraded and expanded over time, leading to the current 5,614 kilometre extent of the barrier being reached in the 1950s.

On the inside of the dingo fence, which contains cities such as Brisbane, Melbourne and Sydney, dingoes were systematically exterminated. This has allowed researchers to examine the effect of the dingoes on the landscape, and how the predator’s removal has affected Australia’s ecosystems.

For example, populations of kangaroo, rabbits and emu are significantly higher inside the fence than they are outside. Rising numbers of these animals mean that overgrazing is increasingly common, reducing the availability of food for birds such as zebra finches.

In the long term, a lack of dingoes has been linked with changes in soil nutrients, with grazing by kangaroos inside the fence reducing levels of soil phosphorous, carbon and nitrogen which aid plant growth. The fence itself also reduces the ability of animals to migrate over long distances, reducing the spread of seeds across Australia.

There have been some calls to remove the fence to help to restore the area’s ecosystems, but with the fence having been around for over a century in one form or another, it’s not understood what would happen to the species that are split by it.

The current study aimed to assess how red kangaroos are being affected by the fence as part of ongoing work to understand the true extent of its effects.

How is the fence affecting kangaroos?

Sampling of the kangaroos on either side of the fence found that, in line with previous research, there were more kangaroos inside the fence than outside of it. In particular, young and female individuals were more common inside the fence.

‘Red kangaroos are one of the dingo’s favourite prey species, so we were not surprised to find fewer of the smaller females and younger animals when there are more dingoes around,’ Vera says.

‘However, we did not expect to see that, on average, young animals inside the fence were lighter and smaller than those outside the fence.’

Animals outside the fence had a larger foot length than those of the same age inside, while young males also had bigger skulls. Analysis of satellite imagery suggested that this difference wasn’t a result of variations in food, but instead differences in development.

The researchers think that kangaroos living beyond the fence have a higher growth rate than those inside to pass through the weight range where they are vulnerable to dingoes more quickly. Alternatively, those inside the fence may have a slower growth rate because the pressure to grow up quickly has been removed.

Co-author Professor Corey Bradshaw says that the ability to grow more slowly might provide an advantage for these kangaroos.

‘Having to put the whole body’s resources into growth, particularly when food is scarce, can mean that other areas of the body are compromised,’ Corey adds. ‘For example, an animal might be in poorer health or have fewer offspring.’

It’s not currently certain whether this difference between the kangaroos is the result of a short-term response to a change in predation pressure, or whether it could be evidence of a heritable genetic change. The team hope further research could help to clear this up.

While both kangaroo populations are expected to survive changes in predation if the fence was ever removed, more vulnerable native species may not be so fortunate. Looking for signs of similar developmental changes in these animals will allow for better management of the wildlife if the dingo is allowed to return to southeastern Australia.