CW: This isn’t gonna be fun. Dead birds, mammals, reptiles, and cats ahead.

The impacts of outdoor cats on wildlife is a well documented topic, with particular interest in the last 30 years. This sensitive topic is one that is incredibly important when considering we are experiencing a 6th mass extinction. Outdoor cats are direct contributors to the spread of diseases and pathogens, kill countless wildlife yearly, and can be a general nuisance. Not only are outdoor cats impactful to the world around them, the lifestyle choice imposed on them are a detriment to them as well.

Predation

Incidental take, defined by USFWS as an unintentional, but not unexpected, taking. This is how we can generally describe the “take” or killing of wildlife by cats. There are a myriad of other forms of incidental take such as collisions with man-made structures, vehicles, or poisoning. Outdoor cats and their global introduction can be viewed as the most impactful form of incidental take and as an invasive animal issue. They have contributed to multitudes of extinctions throughout the world, and untolds more that were never discovered and documented. With this growing issue we want to outline the issues, the impacts, and solutions. In the United States alone, it is estimated that domestic cats kill 1.3 - 4 billion, with a B, birds a year. And that’s just birds. Mammals are estimated at 6.3 - 22.3 billion annually (1). They have contributed to roughly 63 extinctions of birds, mammals, and reptiles in the wild (2). Cats are opportunistic feeders meaning they are fairly indiscriminate as to what they kill and eat. On top of that, all cats exhibit a behavior called surplus killing or killing more than they can and will eat (3). This means no matter how much you feed your outdoor cats, they will kill animals. Cats are inside and out absolute killing machines.

“Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals.”

— Loss, S., Will, T. & Marra, P. The impact of free-ranging domestic cats on wildlife of the United States. Nat Commun 4, 1396 (2013).

Another common deflection is “My cat isn’t a hunter. They just sit around.” Kitty Cam Project by University of Georgia set out to answer some questions about cats, one of them being their predation impacts. The cats recorded killed an average of 2.1 animals per night, per cat. Of these killings, only 23% were brought home and a whopping 49% were left at the kill site(4). This means that even our most precious beloved cat that could never hurt a fly… well that probably isn’t entirely true. This also means that most estimates on predation, i.e. the paragraph just above this one, are aggressively conservative on the true numbers. For the sake of conversation, if 26 billion birds and mammals are estimated conservatively at roughly 23%, then the full 100% would be closer to 113 billion animals using that projection in the US alone.

The general assumption is also that they only kill birds, or at least prefer them. In fact, 41 percent of animals killed during the study were reptiles, while birds constituted just 12 percent of the overall prey. And of course, it is worth mentioning that this only accounts for cats in the United States, roughly 82 million household cats. It is estimated that cat populations worldwide are 600 million. This would put the estimate made on US cats, when applied to global cat populations, puts global native wildlife death at roughly 975 billion animals annually. This isn’t part of our natural process, cats are invasive species and no part of them being outdoors killing native wildlife is “natural.” Animals haven’t evolved alongside them, lacking adaptations to avoid predation from small felines. Not to mention, no other wild animal has this level of unprecedented access to care, meaning that cat populations will never dwindle like some overpopulated wild animals may. Not only is it not natural, it is entirely unnecessary. You feed your cat. You play with your cat. Your cat does not need to be outside for food or enrichment.

Many of the species affected seem to us as pests, but they are vital contributors to our local ecosystems. Countless studies show a steep decline in insect populations globally, certain reptiles and amphibians are also being incredibly impacted by climate change and pollution, and all of these animals serve as food for others in their ecosystem web. All of that is crumbling for many reasons, but one of the most directly impactful is outdoor cats. Please please please, for the love of wildlife keep your cats inside.

Disease

Our little killing machines are also our little disease vectors. There are a myriad of diseases transmissible from pets to wildlife, but the most directly impactful that cats are wholly responsible for is toxoplasmosis. This is a disease that results from the parasite, Toxoplasma gondii. It is of particular concern to expecting mothers, as it can be passed from mother to infant and be fatal. It has also heavily impacted wildlife such as Sea Otters, Enhydra lutris (5). Bioaccumulation of this parasite has also been found in Orcas (Orcinus orca) that have washed ashore, assumed due to fatal toxoplasmosis infection (6).

Toxoplasma gondii is transferred from infected feces, prey, or from mother to offspring. Your cat does not have to be an outdoor cat to contract toxoplasmosis. They could have gotten it from birth, ingesting other animals before you adopted them into your home, etc. Any cat can have toxoplasmosis. T. gondii reproduce exclusively in the digestive tract of felines, spread through the ingestion of feces or tissue infected by the parasite. This means just the simple act of your cat pooping outside can be detrimental to wildlife populations. Because of this, please please please do not flush your cat’s waste also.

Other diseases and parasites that cats help spread are rabies, feline leukemia, fleas and ticks, and much more (7). The Florida Panther, Puma concolor coryi, has seen population decline due to feline leukemia which was traced back to a single domestic cat (8). One.. single.. household cat pushed an entire population of an endangered species to the brink of extinction. Not a colony of cats. A single cat.

Feline leukemia virus threatens endangered panthers (10)

Hybridization

Interbreeding of domestic cats and native wild cat species can and does happen. These breeding events can lead to extinction of native genetics either directly or indirectly. The phenomenon of “genetic swamping” can be seen throughout different wildlife populations in which there is no fully native genetics left. This can make species less genetically successful and also makes conservation of said species difficult. Domestic cats can pose a real risk to wildcat conservation through hybridization, especially when wildcat densities are low (7).

Outdoor Death Sentence

Probably one of the most persuading facts to keeping our cats indoors is the impacts on their life. Outdoor cats face predation, disease, exposure, poisoning, and so much more being outside. We have all had or known a cat to succumb to the many dangers that outdoor life has to offer. 5.4 million US cats are hit by cars each year, 10,000 cats die from antifreeze poisoning each year, and more. And ultimately the owner is at fault for this. Not traffic restrictions, not coyotes, not irresponsible drivers, not antifreeze users; us. Statistics show that indoor cats live a longer, healthier life. Averaging 10-15 years, while outdoor cats can be less than half that (9). After all that risk, regardless of their impact on the world around them, the question stands as to why we would let them roam freely.

Solutions

Addressing Trap, Neuter and Release as a solution, American Bird Conservancy (11) point out some glaring issues. Even with TNR, cats continue to pose threats as disease vectors, predation, and more. Studies show that the technique does little to diminish outdoor cat populations. Feral cats can be particularly difficult to handle, leaving for potential injury and severe infection to the handlers as well as the likelihood of that cat escaping. Cats are very difficult to catch, and often won’t be caught twice. Colonies can become attractive dumping grounds for unwanted pets, growing the colonies further. Not to mention it is inhumane to keep cats outside with the previously discussed impact on their lifespan. Most feral cat lifespans are 2-5 years vs 15-20 for properly cared for indoor cats. TNR programs and those who advocate for them are compassionate, but ultimately fall well short of a true solution to feral and outdoor cats. So what can we do?

“TNR programs fail because they do not operate in an enclosed system and cannot spay or neuter a sufficient number of cats to affect feral cat numbers at the population level. Despite the good intentions of many involved in TNR programs, TNR has been found to be a waste of time, money, and resources.”

— American Bird Conservancy

The simplest solution is one we will always be advocates for, keep your cats inside. Supervised outside time, catios, and leash training can be great ways to get our cats exercise and enrichment. Items like clown collars or cat bibs can help decrease predation, but will never eliminate it. Cats are intelligent and highly adaptable, so such devices commonly become ineffective over given time. Giving our cats ample height to utilize indoors can help create an enriching space for them while keeping them safe. Giving them as much playtime, especially after eating, can help keep them active and engaged in life. This can also help with the dreaded 2 am zoomies by the way. Support local cat control and protection plans that remove feral cats. Oppose legislation and local ordinances calling for TNR as the only solution. Supporting legislation requiring cat owners to register their cats and prevent them from roaming free. Support organizations and legislation to make spay and neutering not only necessary, but affordable and accessable. NEVER abandon unwanted cats. Support organizations that seek to relocate feral cats to enclosed sanctuaries or shelters that can properly rehome them to INDOOR ONLY homes. There are many solutions that we can take, but few that we are taking. We have to do our part. Thank you for reading.