The Hawaiian hawk or ʻio (Buteo solitarius) is a raptor in the genus Buteo endemic to Hawaiʻi, currently restricted to the Big Island. The ʻio is one of two extant birds of prey that are native to Hawaiʻi, the other being the Pueo (Hawaiian short-eared owl) and fossil evidence indicates that it inhabited the island of Hawaiʻi, Molokaʻi, Oʻahu, Maui and Kauaʻi at one time. Today, it is known to breed only on the Big Island, in stands of native ʻōhiʻa lehua (Metrosideros polymorpha) trees. The species was protected as an endangered species in the United States, but was delisted in 2020. However, the IUCN classifies the species as Near Threatened.
The Hawaiian hawk measures approximately 40 to 46 centimetres (16 to 18 in) in length. Two color phases exist: a dark phase (dark brown head, breast, and underwings), and a light color phase (dark head, light breast and light underwings). Feet and legs are yellowish in adults and greenish in juveniles. During breeding season one of the pair, possibly the female, has a distinctive yellow forecap area just above the upper mandible.