The Oatmeal got it right. How much do cats kill? Too. Damn. Much.
A study just published in Nature Communications estimates that, in the US alone, domestic cats (owned and un-owned) could kill up to 3.7 billion birds, 20.7 billion mammals (rats, rabbits, squirrels), 800m lizards and 300m frogs every year (even lower estimates are scary: 1.4 billion birds and 6.9 billion mammals). Domestic cats are one of the worst non-native invasive species in the world, according to the lead author of the study Scott Loss, of the Smithsonian Conservation Biology Institute.
Previously it was argued that the number of cat killings was small compared to deaths caused by, say, collisions to windows, buildings or communication towers, or even habitat destruction. But this systematic study finds otherwise.
Perhaps you knew this, but earlier estimates (like that of the Oatmeal) were lower. Loss remarks that it may be because those studies were not conducted with the same rigour or depth as the current study. According to Loss the new estimates indicate that cat killings are causing population decline some species. A 2011 study even recorded extinctions caused by cat killings. The study conducted on islands showed that free-ranging cats caused extinction of 33 species of birds, mammals and reptiles.
Although un-owned cats are to blame for majority of the kills, owned cats kill a substantial number too. What should ring alarm bells for policymakers is the fact that the number of owned and un-owned cats is growing rapidly across the globe. But Loss admits their estimates based on all available data are still not accurate, and more accurate calculations can only made based on better collection of data.
Methods currently in use to bring these killings under control involve trapping feral cats and sterlising them to stop their colonies from growing. Although this may seem like a good idea, there is no scientific evidence that it works. Loss says, “Management decisions [for controlling cat killings], both in the US and globally, must be informed by fine scale research that allows analysis of population responses to cats and assessment of the success of particular actions.”
While cats with guns (or cats as guns) make for funny pictures, there is more truth to that image than you might think.
Reference: Loss, Will & Marra, The impact of free-ranging domestic cats on wildlife of the United States, Nature Communications 2013. http://dx.doi.org/10.1038/ncomms2380