Around 59 species of pigeons and doves are threatened with extinction today, about 19% of all species. Most of these are tropical and live on islands. All of the species are threatened by introduced predators, habitat loss, hunting, or a combination of these factors. In some cases, they may be extinct in the wild, as is the Socorro dove of Socorro Island, Mexico, last seen in the wild in 1972, driven to extinction by habitat loss and introduced feral cats. In some areas, a lack of knowledge means the true status of a species is unknown; the Negros fruit dove has not been seen since 1953, and may or may not be extinct, and the Polynesian ground dove is classified as critically endangered, as whether it survives or not on remote islands in the far west of the Pacific Ocean is unknown.