What do you see when you look at a house cat? A cuddly, if sometimes roguish or aloof, companion? A skilled and efficient hunter? Perhaps a little bit of both?

Your answer to this question will place you on one side or the other of a growing divide—and billions of lives hang in the balance. These are the lives of the prey—small mammals, birds, reptiles, and even invertebrates—that domestic cats hunt, kill, and sometimes consume each year. They are also the lives of the cats themselves, whether they are mostly indoor pets taking only the occasional stroll outside, semi-feral animals receiving some human support while living in colonies, or completely feral felines dependent only on themselves.

For over a century, naturalists have worried about the potential impacts of domestic cats on native wildlife, and their fears have only grown as improvements in technology have allowed researchers to paint an ever more detailed picture of house cat hunting behaviour. Despite the increasingly damning evidence that our feline friends are slaughtering an unsustainable number of native animals, pro-cat advocates have repeatedly lobbied against efforts designed to protect wildlife by minimizing the ability of house cats to interact with these animals—even where this mitigation involves relatively gentle measures such as mandatory pet registration and cat curfews. Conversations about potential management solutions have been strained, even violent; in at least one case, the discussion led to death threats against researchers who pointed out the harm that cats can do.

Cats, then, are seen by some not only as more important than wildlife, but even more important than humans. How did we get here—and where should we go next?

The ecology of cats

It is hard to know exactly how many domestic cats exist in the world, but researchers estimate there are approximately 600 million, of which maybe a quarter are ferals—cats that are not deliberately supported in any way by humans. Feral individuals are, by necessity, free-roaming, but they are by no means the only domestic cats with an opportunity to explore the habitat and predate native wildlife. Many pet felines, such as the traditional ‘barn cat’, are only loosely affiliated with their owners, and may spend significant proportions of their time outdoors. Likewise, even the cats that spend the majority of their time indoors may be let outside occasionally. A recent study examining both rural and urban households in Australia revealed that only about a tenth of cat owners entirely restrict their pets to an indoor lifestyle. Although practices likely vary according to location and owner demographics, this figure can be used to estimate that approximately 405 million owned cats, plus 150 million feral cats—for a grand total of 555 million cats—are in a position to hunt and kill native wildlife globally.

While domestic cats are not native, many, if not most, of their prey items are, and this contrast is particularly galling to conservationists because it seems like a given that indigenous wildlife should be valued over a species that has been introduced. Many of the animals that cats hunt are not commonly thought of as particularly exciting or charismatic (think voles or skinks, for example), but they all play an important role in their local ecosystem. Reducing their numbers or removing them completely can, among other things, alter the dynamics of food webs, change the ways and extent to which diseases spread through populations, and influence habitat structure by impacting seed dispersal.

The negative impact of cats is particularly obvious on islands, where feline predation has wiped out endemic species (those not found elsewhere) or, at the very least, contributed to their status as ‘threatened’. Particularly well known is the example of the Lyall’s, or Stephens Island, wren, the focus of the first chapter of Pete Marra’s and Chris Santella’s book Cat Wars (reviewed elsewhere in this issue). Lyall’s wrens were ‘discovered’ after a free-ranging pet cat began bringing them home from hunting trips; shortly after the wren was identified as a new species, it was extinct. Although this species was already in a vulnerable position, experts agree that cats drove the final nail in its coffin—and this is not an isolated occurrence. More recently, for example, camera traps have captured footage of cats attacking and killing Hawaiian petrels (also known as ‘ua’u) at their burrows. This species is an endangered endemic that could easily suffer the same fate as the Lyall’s wren in the absence of some sort of intervention.

Island species—birds or otherwise—are especially vulnerable to cats for a variety of reasons. For one thing, many islands to which felines have been introduced do not have any similar native predators; this means that potential prey may not be naturally wary of cats or have sufficient defences or escape mechanisms (ground nesting, as seen in the Hawaiian petrel, is a huge risk factor). For another, resources on islands are finite, and therefore may support much lower numbers to begin with; a good feline hunter might work its way through an entire population fairly quickly, especially if (in the case of non-endemic species) it is not regularly replenished by new individuals from the mainland. Of course, the size of the cat population is also important to consider. Cats are quick breeders; a female reaches sexual maturity in as few as five months and can produce a new litter (of anywhere from two to five kittens) every four months or so. Before long, one or two cats can become a dozen, and a dozen can become a hundred. Even if each of those hunters only takes down a single wild animal a day, the cumulative effects would quickly become untenable, especially for populations that are small, isolated, and/or already struggling in the face of other threats such as chemical pollution or—as in the case of Lyall’s wren—habitat loss.

A growing catalogue of casualties

The effects of cat predation have been somewhat easier to observe and record on islands than on the mainland, where researchers have had to do a fair amount of extrapolating in order to estimate just exactly how many wild animals—and of which species—are being hunted by domestic cats each year. Although ornithologists have been sounding the alarm since at least the early 20th century, most formal studies of cat predation have been conducted only since the 1980s, as conservationists have become increasingly panicked.

One of the reasons so many scientists have revisited this issue is that the tallies of cat-caused casualties are staggeringly high, causing researchers and the public alike to ask, ‘could that be right?’. Yet, no matter who performs the study or what region is examined, the results say the same thing: free-ranging cats kill astronomical numbers of wildlife. One of the earliest systematic analyses calculated that just in the rural portion of the US state of Wisconsin, there were approximately 1.4-2 million domestic cats that were, collectively, responsible for the deaths of some 7.8 million birds each year. More recently, a study conducted in the UK estimated that some 9 million British cats preyed on anywhere from 52-63 million mammals, 25-29 million birds, and 4-6 million reptiles annually. Just this year, researchers found that Australian cats predated approximately 466 million reptiles annually – in addition to the 377 million birds they’d previously been found to kill.

Over the past several years, scientists have made use of a wider range of techniques, including trail cameras, cameras affixed to cats’ collars, GPS tracking, dissection of scat samples and dead felines, and analysis of footprint patterns, just to name a few. All evidence suggests that if the resulting tallies are incorrect, it is only because they are too conservative and actually underestimate the damage that domestic cats are doing each year. This indicates that we can be pretty confident in saying that annual cat kills are well into the tens, if not hundreds, of billions. Cats are known to have contributed to at least 8% of all reptile, bird, and mammal extinctions and approximately 10% of the population declines of all critically endangered animals in these three groups.

Medical consequences

Predation is not the only negative effect of free-ranging cats. While they are out and about in the habitat, domestic felines are exposed to a range of diseases that they can spread to each other, to wildlife, and to humans. Examples include fleas, ear mites, hookworms, roundworms, rabies, avian flu, feline leukaemia, and toxoplasmosis—the last of which can be particularly devastating in pregnant women, and has recently been linked to, among a host of other more flu-like symptoms, a range of behavioural and psychological problems. When infected cats defecate outdoors, the microorganisms they are voiding can enter the water, which not only reduces water quality and places a greater burden on the sanitation process, but also puts wildlife in harm’s way. For example, Hawaiian monk seals exposed to runoff contaminated by cat waste suffer a higher incidence of infection by the protozoan that causes toxoplasmosis—leading to their deaths.

As if it weren’t bad enough that humans and wildlife can contract diseases that are at best unpleasant and are at worst deadly, the cats themselves also suffer. Free-ranging cats have been found to carry higher parasite loads and be infected by more communicable diseases than indoor-only cats. This is one of several reasons why outdoor cats are not only less healthy, but also have shorter lifespans than their indoor counterparts. Truly feral cats may only live a few years (assuming they make it past kittenhood, which most do not) and barn cats may only last a couple years longer; on the other hand, fully indoor cats—protected from hazards such as cars, bad weather, fights with wild animals and other cats defending territories, and the vast majority of diseases—may live well over two decades.

The difficulty of ferals

This discrepancy in lifespan and quality of life is one of the main points that has been emphasised by the activists who argue against allowing cats to roam freely throughout the habitat. Though their message often falls on deaf ears, these crusaders repeatedly point out that we are not really doing felines that big of a favour by granting them their ‘freedom’. The truth is that the vast majority of wild domestic cats lead lives that most cat owners would be heartbroken to imagine for their beloved pets. This is particularly true of ferals, which have the most difficult lives of all, as evidenced by their thin bodies, torn ears, ragged fur, and scarred faces. Whether they live in rural or urban environments, feral cats have to work hard to obtain and defend every scrap of food and sheltered sleeping spot.

Some ferals are looked after (at least partially) by caretakers who devote significant amounts of money, time, and effort to caring for the cats. Some eventually open cat sanctuaries, large-scale rescue operations that remove feral cats from colonies and relocate them to facilities offering safety and regular care in perpetuity. Cat sanctuaries sound like a perfect solution until you factor in the huge expense required, as well as the incredible amount of space that would be needed to accommodate every feral cat currently in existence.

Another appealing alternative is trap-neuter-release, which aims to curtail the growth of existing colonies and more free-ranging feral populations by rendering the cats unable to create kittens. Unfortunately, this method fails to reduce either the cats’ hunting of native wildlife or their ability to spread disease. Further, it assumes that new feral cats won’t appear through other means – by running away from home, for example, or by the all-too-common occurrence of being abandoned by owners that no longer want a pet.

In Australia, where feral cat populations have had a devastating effect on rural wildlife in particular, officials have taken more drastic steps. After years of not just permitting, but also encouraging, hunters to kill feral felines, the government has more recently begun using tailored poisons that target cats and euthanise them quickly and painlessly. Both techniques have drawn backlash from animal lovers who consider these methods inhumane. However, conservationists suggested these measures not just for the purpose of preserving wildlife, but also to bring a humane end to the feral cats’ hardscrabble lives. Although animal welfare is of critical importance to people on both sides of the debate, there are different views of which animals should be prioritised, and how those species can best be managed compassionately and responsibly.

Australian scientists have also investigated support for additional measures such as mandatory registration of pet cats, cat curfews, and outright bans on domestic felines in habitats that are home to sensitive wildlife. Support for these varies according to the demographics of the people being surveyed—gender and location were particularly influential features—but are, overall, surprisingly high. These methods could possibly gain traction in other countries, as well, though, as many researchers have noted, Australians have a more pragmatic and proactive response to wildlife management than is currently found elsewhere.

Seeking a solution

Because we humans love our cats—and because we typically spend time with them when they’re at their sweetest and most innocent—it’s hard to admit that they are just as good, if not better, at killing as they are at cuddling. When we hear their plaintive meows as they look longingly out the door, it can be extremely difficult to refrain from letting them out. However, the research overwhelmingly shows that we should not turn that knob and let them loose—not if we value our wildlife, or our felines’ health, or our own. Instead, we should invest in toys, cat-scratchers, climbing towers, a leash to take them on walks, even ‘catios’ (fully enclosed patios that allow cats to be ‘outside’ without being able to range far and wide). And if, for some reason, we cannot continue to live with our pets, we should never simply release them into the wild; those that manage to survive by fending for themselves will likely live short, unpleasant lives during which they kill native wildlife.

It’s more difficult to decide what to do about the cats that are already living wild under their own auspices. Trapping them all would take significant time and effort, and while euthanising them may be kinder in the long run, it will never be an attractive option even for the most conservation-minded of people. More governments may begin to follow the Australian model and pursue this option, but places like the UK and the US aren’t yet ready to take this step. There, researchers are threatened and smeared simply for discussing the facts and requesting a dialogue; in the UK, even the Royal Society for the Protection of Birds (RSPB) refuses to publicly admit that cats are a problem, despite ample evidence to the contrary.

Maybe the first step, then, is simply to establish civil discourse—to move beyond suspicion and insults and emotions and instead focus on the cold, hard data. Perhaps then, key stakeholders could finally meet at the table and agree that we need to do something. Once they have achieved that, they would be on firmer footing for having the much more challenging conversation about what, exactly, should be done to avert the ‘cat-astrophe’ before it is too late.

Caitlin Kight is an educator, communicator and scientist. She is the author of the natural history book Flamingo.

Upasana is an illustrator from Kolkata who believes in creating greater represntation of brown women, queer and trans people in their work. Apary from illustrating they organize an LGBTQ art space in Kolkata.

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