Native Bush Rats reclaim territory from black rats in Sydney

In the battle of ‘native wildlife vs introduced invaders’, it’s the natives that are winning at North Head Sanctuary in Sydney where Australia’s small Bush Rats are successfully reclaiming their territory from gangs of invasive black rats.

Results from recent wildlife surveys found that the population of black rats at North Head has decreased from an estimated 112 in 2019 to 29 in 2020. The decline continued in May 2021, when only nine black rats were captured during a survey of 250 hectares at the sanctuary.

Australian Wildlife Conservancy delivers conservation science projects including survey work such as this at North Head Sanctuary which is managed by Sydney Harbour Federation Trust. The significant decrease in black rats is directly linked to the reintroduction of 170 Bush Rats between 2014 and 2016, which were released as part of a unique initiative to use native wildlife to outcompete a foreign species and act as a biological control.

W Lawler/AWC

Australia’s Bush Rats are territorial. As they gain strength in numbers they are able to keep out competitors and reclaim their land from seemingly stronger species such as black rats. At North Head, reintroducing this native species after reducing the number of black rats is blocking reinvasion by introduced rodents.

“Bush Rats and black rats may fall under the same category of rodents, but they impact the environment differently. Bush Rats are native and support the local ecosystem by pollinating local trees and flowers right to the tip of each plant,” said Viyanna Leo, Australian Wildlife Conservancy Wildlife Ecologist. “Bush Rats co-exist with other native species and their presence prevents damaging species such as black rats from consuming the eggs of endangered ground-dwelling mammals and birds.”

W Lawler/AWC

“It’s very exciting that this initiative to reintroduce native wildlife in order to remove pests has worked and to have a success story that sees Bush Rats take back their territory from an invasive species.”

Daniel Sealey, Director of Planning at the Harbour Trust said protecting the threatened flora and fauna at North Head Sanctuary is a key priority of the Harbour Trust.

“It is very pleasing to see the native wildlife numbers continue to grow as these threatened species further establish their presence at North Head thanks to the Australian Wildlife Conservancy who have worked with the Harbour Trust to re-introduce these species to the site,” Daniel said.

W Lawler/AWC

Wildlife surveys at North Head Wildlife Sanctuary in May 2021 also revealed that populations of small mammals remain strong despite a hazard reduction burn that broke containment lines and destroyed 57-hectares of the headland in October 2020. Australian Wildlife Conservancy was not involved in the burn.

Four Brown Antechinus were discovered in Elliott traps during the survey – the highest number of live captures since this species was reintroduced to the sanctuary in 2018. Ecologists believe fires may have displaced individuals from their usual habitat leading them to seek shelter near the survey area. Twelve Eastern Pygmy-possums were also recorded including five new individuals and five females with pouch young, indicating that they are breeding and doing well post-fires.

For more information on Australian Wildlife Conservancy and Harbour Trust’s work at North Head Wildlife Sanctuary, click here.

This topic was covered by Australian Geographic. To read the article, click here.

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