April 24, 2024

Attracting foxes can make feral cats even more ‘brazen’, study of 1.5 million forest photos shows

Foxes and cats kill around 2.6 billion mammals, birds and reptiles across Australia every year. To save native species from extinction, we need to protect them from these introduced predators. But land managers tend to focus on foxes, which are easier to control. Unfortunately, this can have unintended consequences.

We wanted to find out how wild cats respond to fox control. In one of the largest studies on this issue to date, we worked with land managers to install 3,667 survey cameras in a series of controlled experiments. We studied the effects on cat behavior and population density.

Our research shows that feral cats are more abundant and bolder after foxes are suppressed.

In some regions, cats need to be managed alongside foxes to protect native wildlife.

This camera trap captured a wide range of animals, not just cats and foxes, in the Otway Ranges, 2019 (Matthew Rees)

Read more: 1.7 million foxes, 300 million native animals killed every year: we now know the damage foxes cause

Could feral cats benefit from fox control?

Foxes and cats were brought to Australia by European settlers more than 170 years ago. They now coexist across much of the continent.

Although foxes are larger than cats, they compete for many of the same prey species.

But most wildlife conservation programs in South Australia only control foxes. This is mainly because controlling foxes is relatively simple. Foxes are scavengers and readily take poisonous bait. Wild cats, on the other hand, prefer live prey. Therefore, they are much more difficult to control with bait.

Consequently, foxes have become the most widely controlled invasive predator in Australia, while control of feral cats has been relatively localized.

Some native species thrived after fox control or eradication, but others continued to decline. For example, one study found that the numbers of common possums, western quolls and Tammar kangaroos increased following fox control in southwestern Western Australia. However, seven other species fell: dunnarts, woylies, southern brown bandicoots, western possums, voles, brush-tailed phascogales and western kangaroos.

People suspected that controlling foxes might inadvertently free feral cats from competition and aggression, especially if there were no dingoes around.

An image of a red fox on a camera trap in the office.
Foxes devastate native wildlife, but they can also suppress feral cats.
Matthew Rees

Experimenting with fox control

To investigate how cats respond to fox control programs, we worked with land managers to carry out two large experiments in south-west Victoria. Foxes are the main predators in these forests and woodlands because the dingoes have now been removed.

We studied cat behavior and population density before and after fox control in the Otway Ranges. In a separate study, we compared conservation reserves with and without fox control in the Glenelg region.

We launched 3,667 research cameras in seven years. The cameras photograph animals as they pass by, allowing us to analyze where and when invasive predators and native mammals are active.

From these photographs, we were also able to identify individual wild cats based on their unique coat markings.

When several photographs of a cat were taken by several different cameras, we were able to track its movements. Combining information about the tracks of all cats in an area allowed us to estimate cat population density.

It was a meticulous process. We manually analyzed nearly 1.5 million images to check for animals, eliminate false triggers, and identify individual cats.

Future research is exploring the use of artificial intelligence to speed up the process, but the computer still needs to be taught what to look for.

A grid of six different still camera trap images showing a variety of different wild cats
We identified 160 different feral cats in two fox control programs in south-west Victoria.
Matthew Rees

What we found

We found that intensive and sustained fox baiting worked. Areas with more poison bait had fewer foxes. Replacing baits regularly also paid off.

Feral cat density was generally higher in areas with fox control. The strength of this effect varied with the extent and duration of fox management. We found up to 3.7 times more cats in fox-baited landscapes.

Productive landscapes also supported more cats. There was about one wild cat per square kilometer in wet forests, compared to less than half in dry forests.

Feral cat behavior also varied depending on fox control and forest type, including the cats’ visibility, the distance they moved, and the times of day they were active.

Feral cats seemed more adventurous where fox populations were suppressed. In dry forests, for example, foxes were largely nocturnal, as were most native mammals. Feral cats became more active at night when there were fewer foxes, potentially giving them access to different prey species.

We found that some threatened species, such as long-nosed potoroos, were doing much better in areas with long-term fox control, although others, such as southern brown bandicoots, showed no improvement.

We don’t know how fox control has affected smaller native rodents and marsupials, which are likely to be at greater risk due to increased predation by cats.

Camera trap image of one of the wild cats
Areas where foxes were controlled had more feral cats. They also tended to behave differently.
Matthew Rees

A conservation balancing act

Large-scale fox control is an important tool in the ongoing battle to protect Australia’s wildlife. Fox bait is relatively simple and effective. But we have to balance the known benefits of fox control with the potential unintended consequences.

Our study reinforces the need to carefully consider what could happen if you controlled just one pest animal, and to monitor carefully, rather than assuming that fox control will benefit all native species. We’re not saying people should stop baiting foxes, because there are clear benefits for species like long-nosed potoroos. But we need to keep an eye on cats and also manage their impacts on native prey.

Because feral cats are notoriously difficult to control lethally, indirect management can also be useful. For example, promoting dense understory vegetation for native prey to hide in or removing other food sources that increase cat numbers, such as harmful rabbits.

Integrated pest management is challenging and expensive, but probably necessary, especially where feral cats or other pests thrive alongside foxes.

Read more: 10-Year Feral Cat Plan brings us one step closer to adequately protecting endangered wildlife

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