Humans arrived in New Zealand less than 1,300 years ago. At that time the country's only mammals were bats (which flew there), and pinnipeds and sea lions (which swam there). This meant that all the ecological niches occupied by mammals in other lands were occupied in New Zealand by either insects or birds. Because of this, the country has an unusually large number of flightless birds, of which only the kiwi, and the kakapo survive. 