Ringtail opossums are an Australian wildlife species that is potentially endangered  A number of ringtail opossums that had been orphaned and subsequently raised in captivity were monitored after being returned to the wild  Seventy-five percent of those opossums were killed by foxes, a species not native to Australia
Conservationists concluded that the native ringtail opossum population was endangered not by a scarcity of food, as had been previously thought, but by non-native predator species against which the opossum had not developed natural defenses
Foxes, which were introduced into Australia over 200 years ago, adapted to the Australian climate less successfully than did some other foreign species.