> We estimate that free-ranging domestic cats kill 1.4-3.7 billion birds and 6.9-20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality.
From the text of the paper, "majority" means 69% for birds and 89% for mammals. Feral cats kill a lot of animals, because that's what they eat. Pet cats do not. "Domestic cat" here means F. catus, not cats that live in homes.
Also, i wouldn't attach complete confidence to this paper. Firstly, it was written by bird conservationists, who have a dog in this fight (as it were). Secondly, it contains some dubious numbers (eg bird return rate per owned cat per year of 4.2 - 18.3 in US and Europe studies - and yet my mum's cats all brought in 0 - 1 per year). I'm not saying ignore it, but don't treat it as gospel - and it would be great to see responses to it, and other work on this subject.