“Cats cause the extinction of 33 species” is an often quoted line. It’s everywhere, even on Wikipedia and the BBC. Although Wikipedia makes the factual and unconditional statement:
“Their [cats] introduction has caused the extinction of at least 33 endemic species on islands throughout the world.”
While the BBC state:
“….and they [cats] have been blamed for the global extinction of 33 species.”
One site, IFLScience! states:
“Cats – spread around the globe by their two-legged slaves – have been responsible for at least 63 extinctions of mammals, birds, and reptiles.”
They have somewhat exaggerated things don’t you think? The bending of data is due to the authors’ dislike of cats.
But it is worse than that on some prominent sites (although others are more accurate and circumspect).
Wikipedia is perhaps the worst offender. Their reference (source of information) for their statement is a study: Nogales, Manuel; Vidal, Eric; et. al. (1 October 2013). “Feral Cats and Biodiversity Conservation: The Urgent Prioritization of Island Management“. BioScience. 63 (10): 804–810. Retrieved 12 May 2018.
I tracked down this study. The summary states:
“The domestic cat is one of the most damaging species introduced to islands, being a primary extinction driver for at least 33 insular endemic vertebrates.”
Note the word “driver“. It does not say that cats caused the extinction of 33 species. It says that cats (specifically feral cats introduced by people via domestic cats) are a primary driver for species extinction, implying there are other reasons for these extinctions.
This study refers to another study: Medina et al. 2011. The full title is: A global review of the impacts of invasive cats on island endangered vertebrates.
In this originating study which seems to be the source of all the statements on the internet about cats causing the extinction of 33 species it says in the conclusion:
“Cats have contributed to a minimum of 14% of all bird, mammal, and reptile extinctions and the decline of at least 8% of critically endangered birds, mammals, and reptiles…..“
Note the word “contributed“. That does not mean cats caused the extinctions. It means what it says. There are other reasons and the cat (feral cats) compounded the problem. The other reasons are human activities. And to reiterate: humans are the originators of cats on islands. They put them there.
This may seem to be a minor point to make but it is important. The internet is a hotbed of factual inaccuracies caused by constantly passing on information from one site to another.
The inaccurate reporting in this instance colours the views of hundreds of millions of people who don’t know better and who rely on the internet for information. This can lead to an increased dislike of the cat which in turn leads to abuse and calls for authorities to cull feral cats inhumanely. People in authority rely on accurate data but don’t have the time or the wherewithal to read long and detailed studies. They get their information from sites like Wikipedia which are plain wrong. This problem needs to be cleared up, hence this article.
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Ornithologists use estimates on bird kills taken from local studies and extrapolated to national levels. The figures are not necessarily accurate. They like to exaggerate the numbers. Also cats often eat sick and dying birds or even dead birds. We never see dead birds because cats eat them! That’s my theory. And yes feral cats are now part of the ecosystem. Cat haters want feral cats exterminated but as you say what would happen to their prey? An increase in numbers to perhaps intolerable levels. Thanks Randi.
Nobody seems to be able to respond to my query. What would happen if all those alleged billions of birds that cats kill, were not killed? Imagine how many birds there would be in the world. Would the birds then not become virmin? And, how many rats, mice, voles etc would be left alive to the detriment of the human race? And one more thing. Who counts those birds? If cats are eating them and I have seen it happen, they leave almost nothing to let anyone know that they have in fact done this. Sure some domesticated cats hunt for sport, but mostly they eat their pray. I managed a stray cat colony for over 20 yrs and in all that time found maybe 10 remnants.