23 March 2016

Results from a predator exclusion experiment show the devastating impacts of feral cats on northern Australia’s wildlife are far broader than first thought.

In late 2013, two fenced sites, each larger than 50 football fields (64 hectares) were established in Kakadu National Park. It was part of an intensive effort to see whether native mammal numbers improve when feral cats are removed.

“We used a large array of motion detection cameras and cage traps to monitor native animals. Data collected from the fenced sites was compared with four other unfenced control sites to help us determine the response of animal populations in the absence of cats and other predators,” Northern Territory Department of Land Resource Management (DLRM) ecologist Danielle Stokeld said.

The researchers had some success in finding and recording a range of small to medium-sized mammals, including a healthy population of the endangered northern quoll.

“Unfortunately the numbers of small mammals we recorded aren’t yet at levels high enough for us to be able to effectively compare between the fenced and non-fenced sites,” Ms Stokeld said.

However, Project Leader, Northern Territory Government Director of Terrestrial Ecosystems Graeme Gillespie says they did uncover some alarming evidence in relation to reptiles.

“Reptile abundance doubled in the sites where cats had been excluded and diversity increased as well,” Dr Gillespie said.

“Until now the spotlight has largely been on the impact of feral cats on native mammals, but this evidence suggests that this impact is translating more broadly to a wide range of other species.”

The results of the experiment have also significantly boosted ecological knowledge of feral cats within the park. The researchers investigated the diets of both feral cats and dingoes by analysing their ‘scats’ or droppings. They found native mammals dominated 75 per cent of cats’ diets, while a large proportion of dingoes’ diets contained macropods, such as wallabies and wallaroos. Both species appear to be targeting medium-sized mammals such as bandicoots.

Predator proof fence in Kakadu National Park, photo NAER Hub

Kakadu National Park manager Pete Cotsell said feral cats were known to prey on native species, particularly reptiles, birds and ground-dwelling mammals.

“Feral cat management is a priority at Kakadu and this research is critical to understanding the threat cats pose to our native animals,” Mr Cotsell said.

“Further research will help us develop strategies to effectively manage feral cats and their impact on our park.”

Northern Territory Government Director of Terrestrial Ecosystems Graeme Gillespie says the project has been part of a much wider research effort across northern Australia to understand the range of factors implicated in the decline of fauna.

“Cats are only part of the problem. We know that inappropriate fire regimes, combined with the impacts of introduced herbivores, such as feral pigs and buffalo, are having a significant impact on the habitats in which our natives take refuge,” he said.

“Controlling cats is not easy. Knowing how significant cats are in the role of mammal decline is critical to making effective decisions about where to best allocate resources for biodiversity conservation,” he said.

Australia’s first Threatened Species Commissioner Gregory Andrews endorsed the research.

“Feral cats are widely known to be the single biggest threat to our mammals, but many people don’t realise the damage they inflict on other threatened species. This study helps show the devastating impact they have on reptiles as well,” Mr Andrews said.

The project was funded under the Australian Government’s National Environmental Research Program and extended through the National Environmental Science Programme. You can also view videos of presentations made by Dr Gillespie and Ms Stokeld on Vimeo. The project report will be available on the Hub website in November.

Top image: Feral cat captured on a motion detection camera, photo DLRM