Oʻahu nukupuʻu bill to pluck insects found underneath tree bark, the Oahu nukupuu fed on insects on flowering trees such as the koa ("Acacia koa") and ohia ("Metrosideros polymorpha"). These trees attract a large amount of insects due to their nectar-filled flowers. The Oahu nukupuu fed on koa in high elevation forests and fed on ohia in low elevations. The species was believed to have vanished as the spread of disease occurred, killing off nukupuu populations across the islands. In order to control the rat population in the sugar cane fields, mongooses were introduced to Hawaii and were suspected to be predators
Koa people as the centre, they extended north as far as Kynuna. Their western boundary lay around Middleton Creek, wshile to the east, their frontier was at Winton and Sesbania. Their southern limits were around Cork. Neither circumcision nor subincision played any part in the Koa's initiatory rites into manhood. At least one Koa Bora ground, a gibber clearing threaded with portoluca, used to exist close to the homestead on Carisbrooke Station, southwest of Winton. Comparatively little is known of the Koa, and, in one modern tradition of whites in the area, they just 'melted away' when Europeans began to settle in