I recently published a Hot Topic on feral cats for the Ecological Society of Australia.
Hot Topics are evidence-based syntheses of topical environmental issues and they include a database of studies relating to the topic. You can find the summary text below and access the full synthesis here.
The domestic cat (Felis catus) was introduced to Australia by Europeans and now inhabits all of mainland Australia, Tasmania and a number of offshore islands. Feral cats are opportunistic, generalist carnivores and their potential impacts include: predation, competition and disease transmission.
The recent Action Plan named feral cats as the number one threat to endangered mammals and Federal Environment Minister, Greg Hunt, has called for the ‘eradicat[ion] of all significant populations of feral cats’ within a decade.
Cats prey on at least 400 native and introduced vertebrates in Australia, including 123 birds, 157 reptiles, 58 marsupials, 27 rodents and 21 frogs. Cats have played a key role in the extinction of at least 20 mammals, and are a current threat to several threatened mammal and bird species. Most evidence for the population-level impacts of feral cats has been gleaned from historical patterns of decline and extinction, or from the failure of reintroduction attempts for threatened mammal species. The small amount of experimental work that has been done confirms that cats can suppress and exterminate small mammal populations.
The impacts of competition and disease transmission are less clear. Overlap in resource use between cats and native predators suggests competition may exist, although this has not been confirmed experimentally. Cats carry the parasite Toxoplasma gondii, which can cause death for many marsupials. High prevalence of Toxoplasma antibodies has been recorded in some marsupial populations, although it is not known how infection might alter their behaviour or susceptibility to predation.
Further research into the non-lethal impacts of cats is necessary, as well as a better understanding of the relationship between cats, other predators and their prey.
Recently, I was lucky enough to talk about my PhD research on feral cats on Radio National’s Science Show, which is presented by Robyn Williams on Saturdays between 12 and 1pm. I discuss a quantitative review of feral cat diet in Australia that I conducted with a group of colleagues. We found that cats consume 400 vertebrate species in Australia, including 16 globally threatened taxa. You can listen to the radio audio here and read more about the study here.
Australia is home to more than 300 species of land dwelling mammals. 85% are found nowhere else in the world. Since Europeans arrived in Australia, just over 200 years ago, 30 mammals have become extinct. This is the highest rate of mammal extinction anywhere in the world. The main culprit for the decline is predation by the introduced red fox and feral cat. Feral cats have recently been named the biggest threat to Australian native mammals. They are eating their way through our wildlife. Tim Doherty is studying the ecology of feral cats in Charles Darwin Reserve, 450km NE Perth. Dissection of cat faeces and stomach contents reveals they predate on almost anything. Tim hopes to collect information which will be useful to land managers as they attempt to control feral cats and protect native fauna from these introduced killing machines.
Feral domestic cats are a global threat to biodiversity and were recently named as the biggest threat to endangered Australian mammals.
But what about your pet cat, or the local stray? While any kind of domestic cat can kill wildlife, there’s no “one size fits all” way to manage their impact.
Before we figure out how best to manage cats, we first need to distinguish between the different categories.
What’s in a name?
There are likely more than 10 million feral cats in Australia, and each year tens of thousands of stray cats are put down in Australian cities.
But there are several ways to classify cats. They include: pet cat, house cat, domestic cat, stray, feral, semi-feral, unowned, colony cat and free-roaming, amongst others.
Despite the plethora of systems, we can make a couple of generalisations. Common characteristics that are used in defining different groups of cats include their degree of socialisation, ancestry, ownership, fear of humans and reliance on humans for their care.
The broadest two groups that can be identified are “owned” cats, which live in a household where they are fed and cared for by humans, and “unowned” cats that do not live in a household and may or may not be fed or cared for. The term “free-roaming”, on the other hand, can include both owned and unowned cats, since it generally refers to a lack of confinement.
Both owned and unowned cats can kill wildlife, so the term free-roaming is useful for management in cities where both groups co-exist.
Stray or semi-feral cats are those that were once owned and part of a household but have since become lost or dumped by their owners. Stray cats are partly or wholly dependent on humans for the provision of food and shelter and colony cats are stray cats that live in groups fed by members of the public, but are not officially owned or cared for.
Feral cats on the other hand, have no degree of socialisation or dependence on humans.
Claws for concern
In Australia, feral cats outnumber stray and pet cats in terms of both absolute numbers and their relative impacts on native fauna. Feral cats prey on hundreds of species of birds, mammals and reptiles and have contributed to the extinction of more than 20 mammal species. It’s estimated that tens of millions of native animals are eaten by feral cats each night.
Make no mistake though, some stray and pet cats are natural born killers too. The majority of wildlife taken by cats in urban areas are likely to be rats, mice and common bird species, but cats are also a potential threat to endangered species that live in urban areas, like the western ringtail possum in Busselton, Western Australia and the southern brown bandicoot in south-eastern Melbourne.
A matter of life and death
Whether a cat is named as stray or feral could mean the difference between life and death for the animal.
Under New Zealand’s Animal Welfare Act, feral cats can be killed. Killing is acceptable for stray cats too, except where there is evidence of ownership, in which case the cat must be sent to a shelter for at least seven days.
The regulations in Australia are more complex, because each State and Territory has its own set of legislation. Nevertheless, feral cats are recognised as a pest and hence are subject to lethal control across Australia.
Under the guidelines of the International Society of Feline Medicine, stray cats qualify for rehoming, whereas feral cats do not. However, both groups of cats qualify for trap-neuter-return (TNR; a vexed issue in itself), and then “occasionally euthanasia” as a last resort.
Not everyone agrees on the best way to manage cats. One study from the US, perhaps unsurprisingly, found that the opinions of cat colony caretakers and bird conservation professionals were highly polarized, and a study from the UK found that cat rescue workers considered that most cats could be tamed and rehomed, whereas veterinarians generally considered that this was inappropriate for feral cats.
In Illinois, rural residents were more likely to support lethal control of feral cats compared to urban residents , and in Western Australia, cat owners were less concerned about wildlife impacts and were less likely to favour controls than non-cat owners.
How to help
Managing the impacts of different groups of cats on wildlife requires different approaches. Keeping your pet cat indoors or confined to your property can prevent it from killing wildlife.
We asked researchers from ECU’s School of Natural Sciences about some of their favourite Australian wildlife. In this piece PhD student Tim Doherty talks about his choice, the Kyloring or the western ground parrot (Pezoporus flaviventris).
Why would a bird perfectly capable of flying decide to spend most of its life on the ground?
It’s a question you could ask a western ground parrot, however locating one of these critically endangered birds could prove a challenge – it’s estimated there are less than 110 left in the wild.
Australian fauna have suffered serious declines since European settlement, with small- and medium-sized mammals being the worst affected. Feral cats depredate native birds, mammals and reptiles and are listed as a Key Threatening Process under the Commonwealth EPBC Act. Reducing the harmful impact of feral cats on native fauna presents wildlife managers with a formidable challenge.