Don’t let their fluff fool you: your cat is built for murder. Felines, no matter how docile, are highly adaptable carnivores that can put almost anything into their mouths. For owners of free-range cats, the gifts of dead birds, mice and lizards brought home by "good intentions" are all too familiar. An analysis published today in Nature Communications and led by Auburn University ecologist Christopher Lepczyk shows that,There are surprisingly few things cats don’t eat.
Lepczyk's team compiled a century of evidence from studies around the world and identified more than 2,000 species of animals eaten by cats—and that's just what scientists have documented so far. Of these species, 347 are endangered and 11 are listed as extinct in the wild (or permanently extinct). "Scientists have long known that feline predation is an ecological nightmare, but it is an extremely challenging problem that we still have to solve," said Peter Marra, director of the Earth Public Institute and professor of biology at Georgetown University.
Since cats were domesticated in the Middle East nearly 10,000 years ago, they have traveled almost everywhere humans have gone. In order to thrive in so many different environments, cats have become opportunists. Some animals, such as giant pandas and koalas, only eat a limited range of specific foods, and "cats are not diet experts," Marra said. "They're just trying to make ends meet."
For the past two decades, Lepczyk has been gathering evidence about what cats eat—first as a side project driven by curiosity, then as a full-scale scientific study. Cat diets around the world have been reported in hundreds of peer-reviewed journal papers, doctoral theses, government reports and magazine articles over the past century, but until now, this information had not been fully summarized and organized. So his team, which includes researchers from North America, Europe, Australia and New Zealand, pulled out every report they could find about what cats were eating and added every species listed as cat food to the database.
"What we're doing isn't rocket science," Lepczyk said. "But it's necessary." Finding out exactly which animals cats have an impact on will inform future conservation and policy, hopefully to the delight of both endangered species and beloved pet owners. "
There's more than one way to monitor your cat's diet. For years, scientists have studied the contents of cat vomit and litter box feces, and conducted surveys asking pet owners to report the critters their outdoor fur babies brought home. Especially when it comes to feces, it can be tricky to distinguish between something a cat kills and something a cat picks up, Lepczyk said. Elizabeth Gow, a research scientist at Environment and Climate Change Canada and an adjunct professor at the University of Guelph who was not involved in the study, solved the problem by outfitting cats with GoPro-like cameras to record what (and how) they hunt when humans aren't looking. Among other spectacles, Gao captured footage of a cat preying on a rabbit larger than itself.
There are millions of predatory cats roaming around, both feral and domestic, and their need for food causes enormous harm to the environment. For years, pet owners have believed that outdoor cats wreak havoc on birds, and scientific evidence linking cats to bird deaths supports this. Given that other facts of urban development, such as light pollution and habitat loss, have caused bird populations to decline.
But threatened birds are not even half the problem. Lepczyk's team found that while birds (981 species, or nearly 10% of known bird species) account for 47% of the species cats eat, the cats' global diet also includes 463 species of reptiles, 431 species of mammals, 119 species of insects, 57 species of amphibians and 33 species of other small animals such as spiders and crabs. The number of confirmed species continues to increase rapidly with each publication, suggesting that the number of species reported in this new study is an underestimate.
The results are quite conclusive and not unexpected, given the vast body of evidence on which this work was based. Scientists have long known that feline predation is an ecological nightmare -- this paper just proves that cats eat a lot of stuff we didn't know existed. From an animal conservation perspective, this is concerning. Every time we lose a species or a population is affected, ecological integrity is compromised.
This damage may be unevenly distributed across the globe. The paper compiled data from around the world, but stray cats disproportionately plague islands where native species evolved in relative isolation. Cats have been terrorizing Australia since they were introduced to Australia by Europeans in 1788. Cats quickly spread across the continent, and Australia's animals were ill-equipped to deal with such indiscriminate predators. In September 2023, Australia’s Minister of Environment and Water Tanya Plibersek declared war on wild cats. Sarah Legge, a professor at the Australian National University and a member of the Australian Biodiversity Council, said: "We have the largest recorded mammal extinction in modern times, and cats are the main culprit."
The level of understanding of cat diet varies from place to place. Despite the large and well-documented feral cat populations in places such as Istanbul, Rome, and Houdong, Taiwan, studies from outside North America and Australia were significantly underrepresented in this meta-analysis. In other countries, it's harder to draw a clear line between cats and biodiversity loss, Legg said. She said that while there was plenty of evidence linking the presence of free-ranging domestic cats to declines in other species, figuring out whether domestic cats actually contributed to the decline of prey species would require "impossible experiments" such as removing cats from entire suburbs and seeing what happens.
Mikel Delgado, a scientist and certified cat behavior consultant, believes the problem goes far beyond felines. Human actions such as deforestation, intensive farming, urban development and the burning of fossil fuels also harm native species. She believes that "focusing on cats is a bit like scapegoating the larger problem of our ecological landscape. If we are not willing to meaningfully change our behavior, "I don't know why we would be motivated to do anything with a species that is so closely related to us."
A one-size-fits-all approach to reducing cat predation may not work either—cultural attitudes toward cats vary widely around the world. Legg said there was strong support for pet restrictions in Australia because the public was relatively well-informed about the ecological impacts of free-ranging cats and other invasive species. Legge said regional laws requiring owners to keep pet cats indoors would not be as radical in Australia as they were in the United States or Europe, where cats were generally believed to need to roam freely outdoors to be happy.
It’s true that some cats can be absolutely terrifying when locked up in a house. But Delgado says cats usually throw tantrums indoors because their environment isn't conducive to them doing the kinds of things cats naturally do outdoors: exploring, climbing, hunting, scratching. In many ways, Marra says, it's a shame that we have a much stronger sense of responsibility toward dogs than toward cats. Lepczyk said educating people about responsible cat ownership can help them give their cats a fulfilling, safe and eco-friendly life. Building an enclosed outdoor "cat house," training your cat to wear a harness, or taking your cat outside in a pet stroller (my personal preference) will give your pet some outdoor time where they won't kill birds, get into fights, or get hit by cars.
There is currently no good solution that will satisfy everyone, and killing stray cats is generally considered a nuisance, but the TNR (capture-neuter-return) method is generally considered a non-kill alternative and is not effective unless you sterilize a significant portion of the cat population.
But Lepczyk believes continuing to encourage people to keep cats indoors could solve at least part of the problem. He said: "If we don't work hard to create responsible pet owners, we will never solve the problem of outdoor cat ownership. There is no single way to solve this problem. But the more we can encourage responsible cat ownership, the better."