Talk to birders, casual conservationists or anyone who says they’re worried about the ecological impact of cats on native bird and mammal populations, and without fail they’ll bring up The Study.
Yeah, that one: A 2013 study, published in Nature Communications, that claimed cats kill “billions” of prey animals each year in the U.S. alone — including 3.7 billion birds and up to 20 billion small mammals in the contiguous states.
What activists won’t acknowledge is the fact that there are fatal flaws in the research, flaws that have been repeated in a new study claiming cats kill 10 times as many small animals as wild predators.
Let’s break it down:
– The researchers don’t actually know how many animals cats are responsible for killing. Both the 2013 Nature Communications study and the 2020 Animal Conservation study rely on owner questionnaires to estimate the number of animals pet cats kill outdoors and to assign numerical scores to their cats’ “hunting skills.” In other words, the study authors are relying on people who have no idea what their cats are doing outside to give them supposedly accurate figures on how many birds, rabbits and reptiles little Fluffy and Socks kill every year. As for people evaluating the hunting skills of their cats, how exactly do they do that? Do they consult nonexistent scoreboards? Do they find a dead mouse or two and conclude that Socks is the GOAT hunter?
– The people who took the surveys were self-selected. These aren’t random samples. The questionnaires were given to people who actively volunteered to participate in the studies.
- In both cases, researchers supplemented their questionnaire data with estimates of “additional” animals killed by cats. Or to put it bluntly, the research teams invented numbers and plugged them in. They’ll claim they arrived at those numbers via analysis, but again, these are studies that rely on owner questionnaires for the bulk of the predation data. Any conclusions drawn from that data are automatically suspect.
- The 2013 study was centered around a meta-analysis of earlier studies, not fresh data. For the numbers they didn’t have, researchers derived figures from older published studies. For example, they added billions of “kills” to the tally and attributed those phantom kills to “unowned cats.” The problem? No one knows exactly how many stray and feral cats roam America’s streets and countrysides, a fact the research team admitted in the 2013 study: “no empirically driven estimate of un-owned cat abundance exists for the contiguous U.S.,” they wrote.
- The best estimates claim between 20 million and 120 million feral and stray cats live in the contiguous U.S. That’s a spread of 100 million! How can a research team estimate how many prey animals are killed by cats when they can’t even get a fix on the cat population? The numbers matter: If there are only 20 million ferals and strays, each of them would have to kill more than 1,000 animals a year to account for the study estimates.
- Headlines trumpeting the 2020 study say it’s based on GPS data, but that’s only partially true. Yes, the team used GPS data from a small number of cats belonging to self-selected study participants, but that data tells them nothing about how many animals those cats are killing. The GPS data only indicates where cats go when they wander, not what they do. In this study, as in the last, researchers relied on questionnaires, which in turn assumes cat owners have exceptional memories and can account for everything their furry friends do outdoors when no one’s watching them.
The stakes are high, as NPR noted in a story about the 2013 study: The resulting headlines are repeated as gospel in newspapers across the country and on countless news sites, which in turn influences how people feel about cats. They influence politicians and proposed laws as well, with several countries looking to ban outdoor cats.
Nuance, such as the 2013 study’s admission that an unknowable number of animals are killed by “collisions with man-made structures, vehicles [and] poisoning,” is usually left out of those stories.
After all, no one’s seriously proposing an end to the automobile industry despite studies claiming untold billions of animals die as roadkill annually.
A quick Google search turns up hundreds of articles with breathless headlines like To Save Birds, Should We Kill Off Cats?, The Moral Cost of Cats, and Cat Owners Turn Blind Eye To Pets’ Violence. There are alarmist books, too, like the hysterically-named Cat Wars: The Consequences of a Cuddly Killer.
In some Australian territories, authorities have open bounties offering $10 for the scalps of adult cats and $5 for the scalps of kittens. Is this what we’ve come to? Killing baby animals based on hysteria over bunk science?
“It’s virtually impossible to determine how many cats live outside, or how many spend some portion of the day outside,” Wayne Pacelle, former president of the Humane Society of the United States, told NPR at the time. The scientists “have thrown out a provocative number for cat predation totals, and their piece has been published in a highly credible publication, but they admit the study has many deficiencies. We don’t quarrel with the conclusion that the impact is big, but the numbers are informed guesswork.”
And that’s the important thing here: Instead of calling for a mass culling of cats based on wild estimates of their environmental impact, we should be working cooperatively on solutions to curb their opportunities to hunt, starting with simple measures like keeping cats indoors.
We don’t need another study with wild estimates of feline impact on small wildlife. What we need are smart plans and the will to implement them as a society.
(First image credit Earth.com. Second image credit CatsAndBirds.ca. Third photo is Buddy, the Inept Hunter.)
11 thoughts on “No, A Study Did Not Conclude Cats Kill 20 Billion Birds And Small Animals Yearly”
The real heavy hitters behind bird and other small creature losses are climate change, noise pollution, chemical pollution and habitat reduction due to human encroachment.
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Habitat loss is a huge culprit across the board, with virtually every animal from tigers and orangutans in the East, to coyotes and pumas in the west. I really hope we learn our lesson or we’re going to be living on a very lonely planet with no wildlife, just endless human sprawl like Bladerunner’s depiction of the future.
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I think some studies are based on hatred and fear of cats. It’s easier to blame outdoor cats for the reduction of song birds, rather than admit that environmental degradation by development, toxins and climate change play the greatest role. Many “animal lovers” have told me how they loathe cats because they kill birds. Facts just don’t get through their prejudice.
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I’m with the SPCA and Humane Society on this: Cats do have an impact, but the studies claiming cats kill 20 billion animals every year in the US alone are not real studies. They’re meta-analyses of existing studies combined with invented, arbitrary numbers to arrive at the conclusions they did.
If you take a deep dive into those studies, it’s appalling to see what they pass off as legitimate research. And yeah, the authors behind it are people who have been pushing cat-culling for years.
You make a good point in noting we (people) are the primary reason for destruction of wildlife.
Unfortunately, as I wrote, a credulous press just repeats the studies as fact.