The last of the Hawaiian 'oos' this small bird is now presumed to be Extinct following no further sightings since 1985 (1). The head, wings and tail were black (2), whilst the rest of the upper surface was brown fading to a rufous-brown rump (3). The black feathers of the throat were each barred with white, which was particularly prominent in the female bird (3). The central tail feathers were long, and there was a small tuft of greyish feathers under the base of the wing (3). The bill and feet were black but the striking legs were a rich golden yellow and the eyes were a lighter yellow (3).
Due to the rarity of the species for many years very little is known about its natural ecology and behaviour. The Kauai oo was observed to forage in ohia and lapalapa trees (2), and the diet was principally composed of small invertebrates such as cockroaches and spiders although flowers and honey were also eaten (3).
One nest that was observed in a cavity of an ohia tree, held 2 nestlings and both parents were seen to feed the chicks (2). Both the male and female birds were known to sing (3).
Endemic to Kauai in the Hawaiian Islands and once widespread throughout the island from sea level to the highest elevations (4), by the 1970s this species was only found within the Alaka'i Wilderness Preserve (4). In 1981, only a single pair of birds remained, of which the female was lost in 1982 and the male has not been sighted since 1985 (4).
Habitat destruction and the introduction of non-native predators such as the black rat (Rattus rattus) has had a devastating effect on Hawaii's native bird fauna and is the probable cause of the extinction of the Kauai oo (4). Mosquitos accidentally introduced to the archipelago in 1826 also devastated avian fauna by transmitting foreign diseases such as bird small pox and bird malaria for which the native birds had not developed immunity (5). The mosquitos spread through the Hawaiian islands devastating lowland bird populations and the isolated, fragmented populations that managed to survive were at increased risk from chance events and disturbance. It is likely that a combination of these factors produced the final death toll for the Kauai oo.
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