Conservation programs that control foxes in order to protect Victoria's native animals may be inadvertently giving space for feral cats to thrive, according to research by the University of Melbourne.
In a recently published paper, wildlife ecologist Dr Matthew Rees and a team from the university and the Conservation Ecology Centre found that cats in dry forests shifted to hunting at night when foxes were controlled.
The researchers suggested this potentially gave the cats more opportunities to hunt nocturnal native mammals.
This latest research followed similar findings by the team that the density of feral cats increased in the Otway Ranges rainforests after foxes were removed.
The feral cat densities in the Glenelg region in southwest Victoria were also found to be higher in forests with long-term fox control than those without.
"Together, these two papers paint a picture of the uneasy balance that exists between foxes and feral cats," Dr Rees said.
"These introduced predators are everywhere in Victoria, even remote rainforest gullies.
"They share many of the same prey and have caused catastrophic damage to our wildlife."
Dr Rees said the research showed that foxes might influence feral cat behaviour, including where and when cats hunt, and which animals they attack.
"We found that cats and foxes often share the same spot in the forest, but that cats come out at different times of the day depending on whether foxes are more or less active," he said.
Dr Bronwyn Hradsky, who supervised the University of Melbourne research, said Victoria's fox management programs were essential to protect vulnerable wildlife.
"However, it is also important we keep an eye on whether feral cats become more abundant or bolder following fox control," she said.
Dr Hradsky said researchers had wanted to understand why some native species, such as long-nosed potoroos, bounced back in forests after long-term fox control, while others, such as southern brown bandicoots, saw little improvement.
To find out how broad-scale fox baiting programs for conservation affect both pest and native animals, the university's researchers and state government land managers repeatedly put out survey cameras at 1232 sites across two forest regions in southwest Victoria.
They then reviewed and tagged millions of photographs of wildlife, and identified individual cats based on their unique coat patterns.
The data showed that feral cat population densities were often higher where foxes were baited, with the difference ranging from only a slight increase to 3.7 times higher.
Foxes have been controlled to protect native wildlife for decades in some regions of Victoria.
In contrast, feral cats were only declared an established pest species on Victorian crown land in 2018, and broad scale feral cat control programs in Victoria were currently very limited.
Foxes and feral cats were estimated to jointly kill 2.6 billion mammals, birds and reptiles across Australia each year, according to 2022 research by ecologists including Dr Rees.
These estimates, however, were highly dependent on how many foxes and cats there actually were.
Dr Rees' research also showed that the impacts of cats in wet forests are likely higher than first thought.
He recorded approximately one feral cat per square kilometre in the dense wet forests of the Otways - the highest recorded for native forest on the mainland.
In contrast, there were only about 0.3 cats per square kilometre in dry forests of southwest Victoria, although cat numbers were twice as high in some forests where foxes were controlled.
"While more research needs to be done, land managers are likely to face a difficult job balancing the benefits of pest control with potential unintended consequences," Dr Rees said.
"In forests where both foxes and feral cats are abundant, we need to think of ways to protect native wildlife from both predators at the same time."
