It’s no secret that domestic cats are quite capable of killing. In the UK alone, estimates of animals killed by cats are in the millions. They go after birds, small mammals, invertebrates, and even reptiles. Despite this, cats are popular pets, with 23 percent of households in the UK housing over 10 million domestic cats.

A new study published in Ecology and Evolution took a look at the relationship between cats’ predatory practices and their owners’ perceptions. Fifty-eight households with 86 cats took part in the study, and the results indicated that telling cat owners what to do might be as difficult as bossing around the cats themselves.

According to the study, cat owners showed a skewed perception of just how much their cats were killing wildlife. After owners completed a questionnaire predicting the number of prey their cat would bring home, their predictions were compared to the real number. Though owners seemed to have an idea of whether or not their cat was predatory, they weren’t aware of the scope of their cats’ murderous tendencies.

Researchers found that owners did not accept that their pets were a threat to wildlife regardless of how much prey they came home with, and were not open to proposals that they keep their cat indoors. In fact, owners were unwilling to take any measures to control their cats besides neutering.

“If we are to successfully reduce the number of wildlife deaths caused by domestic cats, the study suggests that we should use cat welfare as a method of encouraging cat owners to get involved,” Dr. Jenni McDonald, from the Centre for Ecology and Conservation at the University of Exeter’s Penryn campus in Cornwall, said in a press release.

Co-Author professor Matthew Evans, professor of ecology at Queen Mary University of London, added that perceptions of owners were particularly harmful to conservation efforts.

“Owners naturally disassociate themselves from any conservation impacts of their cat, and take the view that cat predation is a natural part of the ecosystem,” he said in a press release.

Cats likely return home with only one or two items of prey per month, according to previous research. The cumulative effective of a high density cat population is, however, likely to have a harmful effect on the environment.

If cat owners remain stubbornly ignorant of their cats’ murderous extra-curricular behavior, that harmful effect won’t be going anywhere.

Source: McDonald J, Maclean M, Evans MR, Hodgson DJ. Reconciling actual and perceived rates of predation by domestic cats. Ecology and Evolution. 2015.