ʻŌʻū

Behavior

The breeding biology of this bird is unknown, although juveniles were observed in June, suggesting a March to May breeding season. The ʻōʻū's call was an ascending or descending whistle that may break into a sweet and distinct canary-like song.

Its unique bill was apparently adapted for feeding on the fruits of the ʻieʻie (Freycinetia arborea) vine, although when the fruiting season ended the ʻōʻū readily moved both up– and downslope in search of other foods, both native and introduced. In addition to fruits, it fed on insects, and buds and blossoms of the ʻōhiʻa lehua (Metrosideros polymorpha). It was known to have been a nomadic forager that made strong flights to follow seasonally available fruit crops across a broad elevational gradient.

Status

Though it was formerly widespread on the six largest islands of that group, this Hawaiian honeycreeper declined precipitously from the turn of the 20th century. The last recorded sighting was in 1989 on Kauaʻi. It is almost certainly extinct there, but unconfirmed reports occasionally are received from the areas above the Kīlauea volcano on the island of Hawaiʻi. As a consequence, it was retained as Possibly Extinct by The Nature Conservancy for more than three decade after that occurrence. The Nature Conservancy, BirdLife International, and IUCN all now regard the ʻōʻū as Presumed Extinct with no known extant individuals. The largest and most secure population above Waiākea were driven from its habitat in 1984 when the area was devastated by a lava flow from Mauna Loa. The ʻōʻū was restricted to the mid-elevation ʻōhiʻa lehua (Metrosideros polymorpha) forests of the Big Island and the Alakaʻi Wilderness Preserve on Kauaʻi. More recently it became restricted to ʻōhiʻa lehua forest.

The ʻōʻū was one of the most mobile species of Hawaiian honeycreepers. Although it was not very active and usually slow-moving, it had remarkable stamina and when flying, would cover great distances. It is one of the few Hawaiian endemics that did occur on all the major islands at one time and did not differentiate into subspecies, suggesting that birds crossed between islands on a regular basis. Also, there was considerable seasonal movement between different altitudes according to the availability of the species' favorite food, the bracts and fruit of the ʻieʻie (Freycinetia arborea). This probably was the species' undoing, as it thus came in contact with mosquitoes transmitting avian malaria and fowlpox, which are exceptionally lethal to most Hawaiian honeycreepers. Other significant threats to this species were habitat loss and introduced predators. Island species are particularly vulnerable to one or more of these threats because of their low numbers and restricted geographical distributions.

Protection

The ʻōʻū was listed as an endangered species in 1967 under the Endangered Species Act. The Kauaʻi Forest Birds Recovery Plan was published in 1983 and the Hawaiʻi Forest Birds Recovery Plan was published in 1984. These recovery plans recommend active land management, controlling the spread of introduced plants and animals, closely monitoring new land activity or development to prevent further destruction of forest bird habitat, and the establishment of captive propagation and sperm bank programs. The ʻōʻū was last seen in the ʻOlaʻa area (Olaa Forest) of the Big Island. Today this area is protected by a multiparty group including state, federal, and private entities.

Extinction

The species experienced a huge decline in the 20th century. At that time, invasive species were introduced, such as feral cats, small Indian mongooses, and mosquitoes. The mosquitoes spread diseases that the birds couldn't be immune to. The cats and mongooses hunted these birds, and rats ate their eggs. The species was last seen in 1989, and in 2024, the IUCN declared it extinct.