As a relatively small and isolated oceanic island, Norfolk has few land birds but a high degree of endemicity among them. Many of the endemic species and subspecies have become extinct as a result of massive clearance of the island's native vegetation of subtropical rainforest for agriculture, hunting and persecution as agricultural pests. The birds have also suffered from the introduction of mammals such as rats, cats, pigs and goats, as well as from introduced competitors such as common blackbirds and crimson rosellas.