Anyone who owns an outdoor cat has undoubtedly been gifted small tokens from their hunts: birds, mice, maybe even bats. They leave them on the doorstep, your pillow, or other inopportune places as presents for you, their human, to find. But what if, instead of a common mouse, you found a dead Regent Honeyeater, a critically endangered species of bird endemic to Australia? Endemic means that the bird is native to Australia and found nowhere else in the world, so if the population of Regent Honeyeaters that only inhabits a small portion of the east coast of the country disappears, then they would face complete extinction.
Maybe, at this point, you might consider trying to retrain your cat to be an indoor cat, or even set up some type of outdoor enclosure to contain it. But what if outdoor domestic cats weren’t the only problem? What if there were millions of feral cats roaming the streets preying on vulnerable endemic bird species? This is the situation in Australia.
Many countries like the U.S. have developed systems to deal with feral cat populations. For example, the Humane Society of the Pikes Peaks Region has a Trap-Neuter-Return (TNR) program, which is exactly what the name suggests. However, this is a long-term solution, and the Regent Honeyeater population is critically endangered right now, with fewer than 500 mature individuals left in the wild according to the International Union for Conservation of Nature. Even with the implementation of many TNR programs across the U.S., the feral cat population still remains at about 50 million.
The issue is completely different in Australia due to large differences in evolutionary history between the two countries. After the split of Gondwana (a subset of Pangea) 45 million years ago, Australia has been evolving in complete isolation from other continents, which has led to the unique dynamics of its present-day wildlife. Apart from species introduced by colonization over the last few hundred years—which is inconsequential in evolutionary time—Australian wildlife has been following an evolutionary trajectory completely separate from anywhere else in the world. As a result, Australia’s response to the issue of feral cats is completely different than that of other continents. This contrast was jarring to me as an American student spending a semester abroad in Australia. I never heard cats discussed as a monumental issue in the U.S., even in the wildlife rehabilitation and animal rescue centers where I have spent time. What are the reasons for this stark difference? How does this impact global conversations around conservation? With my curiosity piqued, I have spent the last few months trying to understand the causes of, current state of, and possible future solutions to the issue of cats—or rather, too many cats—in Australia.
Let’s start with the biggest difference between the feral cat problem in the U.S. and in Australia: the types of predators. Predatory species in the US such as wolves, bears, foxes, coyotes, cougars, and bobcats, are all eutherian mammals (one of the three superorders of mammals). In other words, U.S. wildlife is exposed to largely native predators with which they have coevolved for millions of years.
Australian predators, on the other hand, are mostly introduced species. Native species like the Tasmanian tiger (now extinct) and the Tasmanian devil (now restricted only to Tasmania) are largely outnumbered by dingoes (introduced around 4,000 years ago), red foxes, feral dogs, and feral cats. The native wildlife have spent the last 45 million years or so coevolving with the Tasmanian devil, the Tasmanian tiger, and other marsupial predators, but is now faced with a range of unfamiliar eutherian predators. This shift was largely the result of European invasion starting in 1788. Dingoes were here already, thought to have been domesticated by Aboriginal peoples as pets, but Europeans brought along cats and dogs, and then introduced foxes so they could hunt them. This relatively quick (again, in evolutionary time) transition has produced a phenomenon called predator naivety: when prey animals are unaware of the fact that introduced predators like cats pose a threat to them.
There is a range of possible explanations for the mechanisms behind predator naivety. The most prominent one, proposed by Alexandra Carthey in 2017 in the science journal “Scientific Reports,” is that the chemical profiles of eutherian and marsupial (the superorder of mammals containing most native Australian mammals) mammals are distinct, and so they emit different cues to prey in the area in the form or urine, scats, and bedding. This means that species that have only evolved to avoid the chemical cues of marsupial carnivores (such as tasmanian tigers and devils) might not pay any attention to those of eutherians (dingoes, foxes, dogs, and cats), and will then be caught off guard when they run into one, making them vulnerable prey.
So basically, the Australian predators that the native wildlife evolved with have mostly gone extinct, and now they face a host of introduced species that they are unequipped to defend themselves against. As a result, many species of Australian wildlife are going extinct or falling into the threatened category. These are species small enough to be prey for a mid-sized carnivore: birds, reptiles, and mammals.
In fact, Australia currently has the unfortunate honor of having the highest rate of mammal extinctions in the world, according to a 2018 report by the Australian Conservation Foundation. One of the main reasons for this trend is all the invasive species, which brings us back to cats: how much harm are they really causing, and what are we doing about it?
The cat, Felis catus, was originally native to the Middle East, and was domesticated between 4,000 and 10,000 years ago, likely by farmers. It was then introduced to Australia during European settlement in the 18th century. There are now somewhere between 2 and 6 million feral cats in Australia, ranging across the entire continent, and between 2 and 4 million domestic cats. In their book “Cats in Australia: Companion and Killer,” John Woinarski, Sarah Legge, and Chris Dickman estimate that cats altogether in Australia kill 3 million mammals, 2 million reptiles, and 1 million birds every day. Not every year, that number is in the hundreds of millions, every day. According to the same book, each individual cat kills 740 native animals each year. Despite this, a study by PETA found that most cat owners aren’t aware of how many animals their cats kill, only seeing 23% of their pets’ victims on their doorsteps on average.
So what is Australia doing to solve this issue? The government’s approach was to issue a bounty in 2015 to cull 2 million cats. This strategy has been adopted by groups like the Australian Wildlife Conservancy with their Feral Cat and Fox control program, as well as by hunters in Australia. This program has also been implementing practices of trapping, indigenous tracking, fire management, creating predator-free fenced areas, and possible gene-drive technology. Other proposed solutions include implementing licensing programs for cat ownership, lacing prey with toxins, using guard dogs to protect native species, spray-trapping, spay-neuter requirements for domestic cats, immunocontraception, putting bells on cats, building cat-runs, and predator avoidance training for animals being released from captive-breeding programs.
While these methods are creative, they aren’t all effective. Shooting cats poses some challenges because feral cats are wary of humans, so shooting needs to be done from a pretty far distance. This can be non-lethal and cause extensive suffering for the cat. Baiting is tricky because cats don’t often scavenge, so the toxins just end up killing other species, which can leave greater resources for cat numbers to skyrocket.
Other lethal strategies for controlling cats, such as traps that spray toxins onto their fur which will later be ingested through grooming, have shown greater success. But is killing cats the only way to address this issue?
Sterilization programs, cat-runs, bells, and licensing programs all mainly focus on domestic cats, which are only a small part of the problem. Many of the people that I’ve spoken to in Australia quickly brush off the topic, saying that they have built a cat run for their own pets. Feral cats tend to be viewed as a byproduct of domestic cats, but at this point, they form completely distinct, wild populations covering the entire range of the continent, which is mostly uninhabited by humans. So those solutions might be effective for domestic cat-owners, but they aren’t getting to the heart of the problem.
Another popular strategy involves releasing native species into sections of land that are fenced off from predators. This is a strong short-term solution to increase the population numbers for critically endangered species, but we need to be thinking long-term for a problem as wide-ranging as this. A short-term solution like captive management makes it difficult to allow native species to re-expand their range, restricting them only to their release sites, and it doesn’t help the wild individuals outside of the fence.
There has been one large-scale fencing operation to combat one of the invasive predators: the dingo. The “Dingo Fence” surrounds an area on the southeastern edge of the continent that’s larger than the state of New South Wales. Although this fence has kept dingoes out, cats and foxes remain inside the area. Building another fence that removes all predators is a possibility, but it would require a huge amount of resources. There are also a number of predator-free islands off the coast of Australia, but these lack the potential for expansion.
Some groups (not just distressed cat-lovers), have started to suggest non-lethal options, positing that the ecosystem of invasive predators in Australia is just too complex for a solution as simple as a bounty. Killing cats might actually have unintended consequences that harm native wildlife in other ways. Killing cats who hunt invasive rabbits and mice may allow these populations to increase and outcompete native mammals.
Instead of trying to euthanize up to 6 million elusive cats, are there ways of managing their ecological interactions in order to protect native species? Research into threatened small mammals has found that they are not only vulnerable due to predator naivety, but also from a lack of physical shelters. This is the product of cattle grazing, introduction of non-native grass species which are a lot shorter than wild ones, and fire suppression. So tighter regulation of grazing as well as prescribed burns might be a more effective and long-term way to help native mammals. This strategy would protect against other invasive predators, not just cats.
Another non-lethal possibility is predator-avoidance training. The University of Queensland is currently testing out this possibility. They are training Northern Brown Bandicoots to associate the chemical profiles of invasive predators with loud alarm calls and foam pellets from toy guns. As an additional measure, the bandicoots are being trained to use microchip-automated doors to access nestboxes. This way, they are the only ones that have access to the nestbox, free of predation and competition.
This solution opens up the possibility for a future where native wildlife and feral cats (and other predators) can coexist in reasonably balanced ecosystems, but it also raises further questions about which species this strategy will actually work for. It’s all well and good to help out the specific individuals reintroduced into an area, but what about the rest of the wild population? What about future generations? Both of these questions are vital to the survival of a species, and they rely heavily on social learning and behavioral plasticity.
Social learning is the idea that when one individual exhibits a behavior, others observing can learn the behavior. If northern brown bandicoots have a high capacity for social learning, then after releasing individuals with predator-avoidance training, we would expect wild individuals and future generations to adopt the same association with invasive predators. If the behavior spread far enough, then this could benefit the entire population. The thing is, the capacity for social learning can vary a lot between species, and there is not very much behavioral research on native Australian wildlife, especially the ones most affected by feral cat predation, seeing as it is hard to find populations to study.
The other thing to consider is behavioral plasticity. This refers to the capacity of a species to change its behavior in response to a changing environment. In this case, it refers to whether or not a species will be able to change its behavioral patterns to avoid invasive predators. The degree of flexibility itself can be strongly linked to genetics, so it is likely that the species that are classified as threatened and have declined due to feral cats are the ones with low behavioral plasticity in the first place. The survival of many Australian species then becomes a question of whether or not they have the capacity for social learning, and whether or not that can compensate for their behavioral rigidity.
Taking a step back to look at all the different strategies to combat the issue of cats, it’s astounding how much thought has been put into this issue, and at the same time, how little. I joke about cat-lovers being overly invested in defending feral cats, but aren’t we all a little biased as Western pet owners and watchers of cat YouTube compilations? Could a 2 million-cat bounty have been an overcorrection for the profound cultural charisma of a species depleting some of the rarest species on the planet?
As an American, this issue was disorienting to step into. Walking through the streets of downtown Sydney, I saw cars with “Feral Shooters of Rural Australia” bumper stickers right alongside people stopping to pet outdoor cats outside of their apartment buildings. Even the larger issue of invasive species is a confusing one that forces us to place value on the lives of non-human animals based on intensely specific distinctions, like whether they arrived on the continent more or less than 45 million years ago, whether they are feral, domestic, or indoors, or whether their population numbers are high or low. This is overwhelming when you are just trying to pet a cat or look at beautiful bird, and it completely dilutes the value of their individual lives.
I definitely don’t know the solution to the feral cat problem, but it probably isn’t guns, and it probably isn’t even hoping that Australia can completely eradicate feral cats, because they are intelligent and adaptable. From conversations that I’ve had here in Australia with researchers, conservationists, and cat-owners alike, which largely either demonize owners of outdoor cats or just focus on less controversial invasive species like foxes, I’ve seen a general discomfort around the issue. This discomfort is understandable, but I’m hoping that as more recovery plans are developed for threatened species and more organizations step up to help, we will have enough breathing room to step back and learn more about these complex trophic interactions in order to see how invasive species fit into our ecological future.
Mommy Issue | December 2019