How Cats Became One Of The Most Delightful Invasive Species


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Nov 26, 2023

How Cats Became One Of The Most Delightful Invasive Species

Outdoor cats are considered one of the worst invasive species by ecologists. And

Outdoor cats are considered one of the worst invasive species by ecologists. And humans are bitterly torn over how to respond.

Carrie Arnold is a freelance health and science writer living in Virginia.

Waking me at dawn is no easy task. A night owl through and through, I am far more likely to see the dawn by just not going to bed. So when my husband announced that he was headed to Old San Juan for some dawn photography, I was inclined to sleep in and join him several hours later at a more civilized hour.

Then my husband dropped the bomb: "I heard there were cats."

He had named the only phenomenon on Earth that could lure me out of bed before sunrise. That's because cats are crepuscular or most active at dawn and dusk. The only spare time we had to glimpse the fabled street cats of Old San Juan in all their furry glory meant that I needed to get my ass out of bed.

Bolstered by my giant travel mug chock full of coffee, I was rewarded with a breezy tropical morning. We arrived at the Paseo del Morro just as the sun was peeking through the clouds, but the mile-long walkway that wove between Spanish city walls and turquoise waters sat nearly empty. As a landscape photographer, my husband was thrilled. As a cat lover, I was not. After 20 minutes of wandering and seeing a solitary tabby flick a disdainful tail in my direction, I began to wonder whether my husband had played a practical joke on me.

Then I heard the electric hum of a small golf cart puttering in my direction. It stopped 10 feet away from me. The motor generated a far more effective version of the pspspspsps that I had been trying for the last quarter-hour. Within seconds, the golf cart was swarmed by voracious, yodeling felines. Cats seemed to melt out of the rocks. I felt like I had been dropped into a scene that resulted from a Vulcan mind-meld of Salvador Dalí and T.S. Eliot.

After filling bowls with kibble and water, the volunteer from Save a Gato, a local nonprofit helping the Paseo's cats, tootled several hundred yards down the path, and the spectacle repeated itself. Some visitors had dubbed the mile-long trail the San Juan catwalk, and a quick perusal of the trail's reviews revealed that I wasn't the only one who enjoyed the feline spectacle.

So three years later, in October 2022, when I read an announcement by the National Park Service that they wanted community input on a cat management plan for the Paseo del Morro, I was confused. The cats almost seemed like they were part of the landscape. But it took only a few seconds for me to realize that no, they aren't. Not really. I gulped hard. Was the spectacle I so enjoyed actually destroying our planet?

San Juan is filled with street cats, many of which are strays and dependent on resident ailurophiles for food. Yet to ecologists, these kitties are one of the world's most dangerous invasive species. Félix López, cultural resources program manager at the San Juan National Historic Site, which includes the Paseo, told me the ongoing presence of more than 100 feral cats along the walkway prevents the park from conserving wildlife and the natural habitat there as it's mandated to do.

"We should not be feeding animals in any national park site," López says. "This is not right for the animal, not right for the environment and this is not right for us."

For nearly 20 years, Save a Gato has been trying to reduce the Paseo's cat population through the trap-neuter-return method, or TNR, as it's known by the feline cognoscenti. This includes spaying and neutering feral and unowned cats, and returning them to their outdoor homes. Cat numbers will decline naturally, and the remaining felines will prevent other cats from elbowing their way into the colony's land. But López says the presence of Save a Gato also leads locals to abandon their unwanted kittens and cats at the Paseo. Many assume that the combination of kitty's natural independence, and the extra food and water the nonprofit provides, will be adequate for their erstwhile pets. As a result, the Paseo's cat population remains massive. Something, López says, must be done.

"This is an area where cats should not have been present from the beginning," he says. "The cats just basically made the site their home."

At community meetings in San Juan, the Park Service ran head-first into local cat lovers who objected to any efforts to manage the Paseo's cats. Management, they knew, meant euthanasia for the animals they had come to cherish. (NPS said they will make their final decision based on public comments.)

Many environmentalists disagree, however.

Forget the Hatfields and McCoys, or the Jets and the Sharks. One of the most vehement conflicts in modern America is between the Cat People and the Bird People. When Dara Wald held focus groups with various feline- and avian-focused nonprofits as part of her doctoral dissertation research at the University of Florida, she had to keep the wildlife organizations separate from the cat groups. Those in cat rescue saw conservation groups as cat haters advocating for modern-day feline pogroms. Conservationists, in turn, painted rescue groups as full of crazy cat ladies whose brains were addled by Toxoplasma gondii, a parasite found in some cat feces. Addressing the cat's impact on the environment, however, requires the two sides to work together.

"It's not black and white," says Lynette McLeod, an environmental psychologist at the University of Canterbury in New Zealand. "It's about sitting down with people and not demonizing the other. It's trying to find solutions that can cater to all parties. There's no easy answer."

So what's a cat lover to do? Until I stuck a tentative toe into this debate, I didn't see an inherent conflict between my love of cats and my deep-seated beliefs in conservation. To a large extent, I still don't. But with an estimated 3o to 80 million unowned cats roaming the outdoors in the United States plus an additional 30% of the country's 60-80 million pet cats allowed outside and global bird numbers in free fall, we must all ask ourselves, which animals do we value, why, and are our cat problems instead human ones.

I have shared my life with cats for 20 years. I love their sandpaper tongues, their commitment to the belief that they are starving and wasting away to nuffinks as soon as the bottom of their food bowl is visible. I love their conviction that not only are cats the best species, but they are also the epitome of what a cat should be. I love how my current cat — a mischievous six-year-old former mama cat named Ophelia — insists that her habit of following me from room to room like a brown- and orange-striped shadow, and curling up between my husband and me on the couch every evening is pure coincidence and most definitely not an indication that she loves us. Not at all.

I also know that Ophelia is a predator. As an indoor cat, her prey is limited to toes, pens and my hair. If she were outside, though, there would be carnage. But then this is why humans started keeping cats around. When humans began farming in the Middle East some 10,000 years ago, they found themselves storing grain surpluses. Lots of grain meant lots of rodents. Just as mice and rats were drawn to the smorgasbord of ready carbs, cats were drawn to the rodent buffet. More courageous cats, who were able to cope with sharing space with other cats, benefitted from the easy access to rodents and whatever food scraps they could scavenge. As a bonus, they got shelter, some protection from predators and the occasional scratch behind the ears. Humans, for their part, got mobile rodent control and an adorable companion. While we encouraged this process, even helped facilitate it, it wasn't done with the same deliberation and care of, say, dogs and livestock. Instead, in an on-brand move for the species, cats domesticated themselves. Well, mostly.

Until the invention of kitty litter after World War II, even the most pampered of pussycats were often let outside to do their business. Whether it's due to less time living alongside humans or some other factor, cats retained a wildness that other house pets and so-called ‘domestic’ animals didn't have. And they still do. Many municipalities in the U.S. have leash laws for dogs, requiring them when off the owner's property. Cat owners, however, often let their pets out by opening the door or installing a cat flap. Finding out where kitty spends their off-hours typically requires reconnaissance with neighbors or attaching a camera to their pet.

This autonomy is much of what makes cats so endearing, says researcher Lee Niel at the University of Guelph in Ontario, Canada. The freedom to roam and ready access to the great outdoors is tied up in what many cat owners believe is fundamental to the very nature of cats. To have a good life — to reach the highest rung of cat-ness — cats need to go outside. In a 2021 study of more than 5,100 cat owners from Europe, the United States, Canada, Australia, and New Zealand, researchers from the United Kingdom's Nottingham Trent University and the University of Edinburgh found that nearly two-thirds of cat owners let their cat outside for the cat's benefit. Kitty's benefit, however, comes at a cost to nature.

One study found that within a one-week period, although 44% of cats successfully hunted outdoors, they only returned with 23% of their prey.

"Because cats only bring a small proportion of their prey home, owners don't really see that impact," Niel says.

Arie Trouwborst, a nature conservation attorney at Tilburg University in the Netherlands, sees this issue as a major problem. Take, for example, many endangered species laws, which institute fines and other penalties for killing protected plants and animals. If you or your child did so, you would be fined. Same goes for your dog. But your cat? There, owners are often let off the hook.

"Many authorities will take the position that these rules do not actually apply, and that that it is okay to let these cats outdoors," he says.

Many cat owners shrug off the issue, Trouwborst says. For some, it's the same disconnect that Niel described in Guelph, a divide between what's known about cat behavior and what some cat owners think about their own, specific cats. To Trouwborst, the bigger issue is our tolerance of unrestrained roaming. The idea of unfettered, al fresco freedom is so elemental to felines — it's what makes a cat, a cat — that we don't question it.

When we see an unleashed dog running free, many of us call the owner or animal control. There's a tacit understanding that a dog must always be restrained, confined or supervised. A wandering kitty, on the other hand, typically elicits a shrug or a pspspspsps. It's reflected in how we hold dog owners responsible for the actions of their pets but more frequently let cat owners off the hook, Trouwborst says. What results, he writes in a 2020 paper in the journal People and Nature, is a giant loophole in endangered species legislation.

"We didn't come up with anything that might constitute a valid justification for not applying the law. So the hypothesis that's left is that this is just politically unattractive for government bodies to engage with," Trouborst says. Their solution? They simply ignore it, he says.

The problem, however, isn't just the occasional feline snacking on one of our feathered friends. Most parts of the environment are so disturbed by humans that a one-off predation wouldn't even be a blip on the radar. The problem is the sheer number of cats roaming the outdoors. Collectively, these house pets have an impact even if each individual cat isn't always a lean, mean, furry killing machine. Although I can't quantify the positive impact my cats have had on my life, their impact on the environment can be. And it's not pretty.

Each year, cats collectively kill billions of birds, rodents, insects, reptiles and amphibians. They routinely make lists of the world's worst invasive species. Free-ranging cats have been implicated in the extinction of Lyall's wren in New Zealand and contributed to the extinction of 33 other species , and are considered a major threat to others, especially on an island like New Zealand — where birds, otherwise, have no natural land predators. To conservationists, it's a major crisis.

Pet cats aren't the only ones causing this murder and mayhem. A major issue that's far more challenging than merely deciding to keep Fluffy inside is the large number of unowned cats roaming our streets and wilderness. One of the biggest challenges is figuring out what the heck to call them.

The most common term is feral cat. Unlike a stray cat that may be fearful but has had some contact with humans, feral cats have limited to no contact with humans and remain highly fearful. Even the friendliest housecat can have kittens that grow up to be feral if they don't become comfortable around humans in their early development, between three to 12 weeks.

"It's not a descriptor with positive connotations," says Kris Hill, a doctoral student in anthrozoology at England's University of Exeter. "It's not an endearment or a good word."

The definition of feral has life-or-death implications. Being labeled as "feral" is often grounds for being euthanized at many animal shelters. Even so-called "no-kill" shelters can euthanize animals with "severe or untreatable illnesses or behavior issues," according to the American Humane Society. In Australia, legislation classifies feral cats as pests and permits communities to poison, trap and shoot the cats under certain circumstances. Some U.S. municipalities have laws banning people from feeding feral cats while simultaneously requiring owners of pet cats to provide them with adequate food and shelter. Same animal, different rules.

Using the word "feral" is a way for us to mentally distance ourselves from the cat — to "other" it, Hill says. As I speak with Hill, I realize that many of us have a disconnect about feral cats that's the flip side of our attitude toward outdoor cats. We think of the feral cat as a cold-blooded killer unlike the beloved sweet kitty — as capable of similar assault — that curls up on our cat tree at home and later, purrs us into a deep slumber.

Feral cats have gained the reputation of being disease-ridden, aggressive and anti-social. There's some truth to this. Unfixed cats fight and yowl at all hours of the day. Cats spray urine to mark their territory, tomcats to signal their reproductive availability, which can leave a musky, pungent smell. Cat intestines are also required for the single-celled parasite Toxoplasma to complete its life cycle, and can cause disease in humans and other mammals. Scientists have identified devastating Toxoplasma outbreaks in marine mammals, infected when contaminated water made its way to the sea. But this doesn't mean that feral cats don't have rich social lives with other cats or that they should be universally reviled, Hill says.

It's a view that's shared by many who advocate for TNR as a humane, compassionate way to reduce the number of unowned cats. Hard evidence on whether TNR works is scarce and inconclusive. So, for that matter, is evidence of the efficacy of euthanizing feral cats. But not everyone believes that TNR is humane or appropriate. Bird conservation organizations like the National Audubon Society and the American Bird Conservancy condemn TNR as ineffective and inappropriate. Spayed and neutered cats still hunt, after all. Even People for the Ethical Treatment of Animals objects, arguing that "although altering feral cats prevents future generations from suffering, it does not protect cats from the litany of other problems that they may encounter.

Allowing feral cats to continue their daily struggle for survival in a hostile environment is rarely a humane option." Often the best option, PETA says, is euthanizing the cats. What's more, the presence of cared-for feral cat colonies encourages people to dump their unwanted cats. The TNR challenges faced by Save a Gato in San Juan are echoed across the United States and around the world.

If humans can't agree on what a feral cat is and what it means to live your life as a feral animal, then it's probably not surprising that we also can't agree on how to approach the problem of feral cats. As Wald spoke to wildlife advocates and cat rescues across Florida, she found that nearly everyone recognized that the state had far too many unowned cats and that communities needed to bring those numbers down. But even this agreement on the fundamentals of an issue isn't enough to convince both sides to work together. Different values and priorities make that seemingly impossible.

Both sides, Wald says, value animal life. Cat advocates told her that their beloved four-legged felines have as much right to life as other animals, and are only one of many species that kill birds and rodents. Birders and wildlife lovers, however, say that the value of wild species far outweighs that of feral and pet cats. Whereas nearly half of all global bird species are in decline, according to a 2022 State of the Birds report by the North American Bird Conservation Initiative, Felis catus isn't going anywhere.

The point of Wald's research isn't to tell communities what species to value, but to figure out how they can come together to address the problem. Officials in Canberra, Australia, for example, created a rule that all newly-adopted cats must be kept indoors, allowing older cats to continue to roam in most neighborhoods. Within a few years, the city's cat population will be exclusively inside-only (or leashed when outside). Miami-Dade Animal Services in Florida has started paying volunteers $15 for every adult feral cat that they trap and spay or neuter.

What made these programs work is the recognition that the problem with cats has nothing to do with cats at all. The issue is a fundamentally human problem. Even basic veterinary care can be inaccessible to some pet owners. We let our cats roam instead of keeping them inside or taking a page from the social media hashtag, #adventurecats, and walking them on a leash. We provide food but don't spay and neuter them. And when we move, we don't or can't always take our cats with us.

Even I, knowing all this, played a part by relishing the presence of the cats along Old San Juan's walkway. While the chances that I will ever turn down the chance to pet a cat are minimal, I also can't deny that everyone — residents, tourists, local wildlife, even the cats themselves — would be better off if all cats had indoor homes and the Paseo was magically feline-free. The presence of so many unowned felines is a human failing, and we owe it to ourselves and the animals we love to do better.

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