Cats are a “beneficial urban predator” according to Dr. John Flux and his conclusion featured prominently in the media to have a major influence on the public debate about cats and native wildlife.
What John describes is possible but the evidence is scant. John’s conclusion and its representation in media has relied heavily on the 17-year record of prey John’s cat, Peng You, brought to him.
There are five reasons why this record cannot be used to conclude that cats are a beneficial urban predator. Here are the first two:
1. Cats kill more prey than they show us –
Cats only bring a fraction of prey to their owner. As few as only 1 in every 5 prey killed by a domestic cat is brought to the owner . Other studies report about 30% of prey , and the smallest estimate of undetected prey that I could find is 50% . Most prey is undetected because it is eaten or left where it is not discovered. John assumes that his cat brought him most of her prey but he has no evidence that this is true. The evidence from other studies is that this assumption is flawed .
2. Cats present us with a biased selection of their kills –
Some species of prey are more likely to be seen because their parts are unpalatable or they are large. Smaller prey is more likely to be completely consumed . Thus, studies like John’s are likely to under-estimate the number of, for example, reptiles and nestlings killed. John concludes the “effect of our cat on reptiles was insignificant”  but he has no evidence that this is true.
Knowing the real and total hunting tally of cats requires that we put tracking devices on them, like radio transmitters or cameras, that enable us to monitor them continuously. Fortunately, such studies are being done . We should rely on their results when making decisions about the impacts of cats on our farms and in our towns and cities, not studies of what one cat brings its owner. Cats kill more than we know about.