Sydney - Australia declared war on feral cats on Thursday with Environment Minister Greg Hunt saying two million of them will be killed to save threatened wildlife.Launching the Threatened Species Strategy at a wildlife summit in Melbourne, Hunt said some $4.8m would be spent trying to eradicate cats from islands and areas of the mainland.Hunt said feral cats have contributed to the extinction of 27 mammal species and threaten the survival of another 120 species such as numbats, bandicoots, betongs and the boobook owl.Cats were introduced to the continent by settlers between the 17th and 19th centuries and there are now an estimated 30 million wild cats. Some grow to three times the size of household cats, and weigh up to 15kg.Hunt said it was time to step in to save Australia's native animals from the predator humans had introduced."By 2020, I want to see two million feral cats culled, five new islands and 10 new mainland areas as safe havens, free of feral cats, and control measures applied across 10 million hectares."Newly appointed Threatened Species Commissioner Gregory Andrews said the cull will use baiting and trapping, and asked cat owners to neuter their animals and not to let them outside to hunt."We don't hate cats. We just can't tolerate the damage that they're doing to our wildlife," Andrews said.Others have suggested using native predators like dingoes and Tasmanian devils to take on the non-native cats.Measures using poisons and trapping "can often be inefficient on a large scale, so what we should be probably doing instead rather is working with nature," Dr Euan Ritchie of Deakin University said.