Native rats reclaim Sydney territory from black rats

By Angela Heathcote 22 July 2021
Reading Time: 2 Minutes Print this page
In the battle of the rats, our humble Aussie bush rat has successfully pushed out and held off the much larger black rat at North Head Sanctuary in Sydney.

“Imagine a war and whichever one gets to the fort first can then win,” explains Australian Wildlife Conservancy ecologist Dr Viyanna Leo. “It doesn’t come down to one being bigger or stronger … It’s more that they are able to defend their territory and hold them out, rather than killing them.” 

As of 2021, just nine black rats have been surveyed within the 250 hectares of the sanctuary, down from 112 in 2019. According to ecologists, this decrease is directly related to the introduction of 170 native bush rats in 2014 and 2016 by the Australian Wildlife Conservancy, with the help of the Sydney Harbour Federation Trust, who manage North Head Sanctuary.

This isn’t the first time that such an introduction was attempted. The Sydney Harbour Bush Rat Project sought to reintroduce native bush rats to North Head back in 2011, however this is the first time that the surveys have found success. “That research helped guide this reintroduction, but this time we did it with a higher number of bush rats,” says Viyanna, which increased the chances of successfully establishing a population. 

Native bush rats were the ideal candidates to hold the fort. “Recent research shows black rats and bush rats both display a competitive advantage when they are the ‘resident’ and can employ aggressive behaviours to defend territories.

“By removing the black rats and reintroducing bush rats into these areas the bush rat is able to become the resident and successfully defend their territory preventing the black rats from re-establishing.”

Related: Here are 7 clever Aussie native rodents
Like much of Sydney, North Head has lost a suite of native species since European settlement. (Image credit: NSW National Parks)

The reintroduction of the bush rats is predicted to create big wins for the local environment. 

“As bush rats previously occurred at North Head we know that the environment is suitable for them,” continues Viyanna, “Bush rats are good pollinators so they will also assist the eastern suburbs banksia scrub with pollination.

“Also bush rats do not like to establish themselves in houses or buildings so despite North Head being surrounded by residential areas the bush rats will not spread into people’s homes.”

Ecologists predict the reintroduction will also result in healthier populations of ground-nesting birds with less black rats around eating their eggs and young.

Viyanna hopes to boost the profile of our native rodents. “I want to be positive about rodents and I want people to understand that native rodents are beneficial to the environment. Not all rodents are introduced, gross and scary. They’re important to the ecosystem”

In the battle of native wildlife versus introduced invaders, Sydney has become an unlikely, but highly able contender for rewilding. “It’s a novel research project, using a native to keep out an introduced species. It just shows that we can rebalance ecosystems if we put in the work.”