Bones of birds have been found near the prehistoric settlements. These settlements existed 500 to 800 years ago. The bones found include those of two species of bird that still visit the island, but do not nest there: The Christmas shearwater and red-footed booby. There are alos bones of four bird species that can no longer be found on the island at all. Polynesian settlers may have driven these bird species, along with six terrestrial snail species to extinction on the island. This loss of a ready and regular food supply may have contributed to the Polynesians' disappearance. The island has been identified by BirdLife International as an Important Bird Area for its endemic landbirds and breeding seabirds.