Evidence shows domestic cats impose an unsustainable harvest on urban bird populations. u003cbru003eu003cbru003eA study in the Netherlands found that free-ranging domestic cats killed an average of 24 birds per year, while another study in the UK found that they killed an average of 55 birds per year. u003cbru003eu003cbru003eHowever, it is difficult to say definitively whether or not this is sustainable, as it depends on the size and health of the local bird population.