Let's not get nasty here. this is interesting evidence quantifying the impact of cats' natural predatory behaviour on native birds. While we don't know numbers, we do know this behaviour is not limited to birds but also applies to our native reptiles (and other small animals).
For whom the bell tolls: cats kill more than a million Australian birds every day, The Conversation, 4 October.
For whom the bell tolls: cats kill more than a million Australian birds every day, The Conversation, 4 October.