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 wilt to the Hawaiian islands. It ranges in size from 15 to greater than 50 feet with a canopy spread of 20 to 40 feet. It has a showy white flower and blooms sporadically. Mature leaves are sickle shaped. Koa wilt is typically a fatal pathogen for its host. In only a few months, a tree may lose its entire canopy and die. Trees less than fifteen years old are typically the most susceptible. Symptoms include stains in cambium, roots, and sapwood as well as chlorosis (yellowing), canopy dieback, brown and wilted leaves, oozing sap, and bark cankers. The Koa wilt