|At Honolulu Zoo, Hawaii|
The Hawaiian hawk or ʻio (Buteo solitarius) is a raptor of the Buteo genus endemic to Hawaiʻi, currently restricted to the Big Island. Buteos tend to be easily recognized by their bulky bodies relative to their overall length and wingspan. The ʻio is the only hawk that is native to Hawaiʻi, and fossil evidence indicates that it inhabited the island of Hawaiʻi, Molokaʻi, Oʻahu, 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 centimeters (16 to 18 in) in length. The female, which weighs 605 g (21.3 oz) on average, is larger than the male, which averages 441 g (15.6 oz). 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.
Common threats to the ʻio are illegal shootings, the degradation of their native forest habitat, poisoning, vehicle collisions, starvation, and predation from other animals.
This solitary hawk remains in and defends its territories year round. They nest from March through September, and usually lay only one egg but sometimes they could lay up to three in their clutch. The female does the majority of sitting during the 38 days of incubation, while the male does the majority of the hunting. After the egg is hatched, the female only allows the male to visit when delivering food to the nest. The chick fledges at seven or eight weeks. Fifty to seventy percent of the nests successfully fledge young.
The ʻio usually hunts from a stationary position, but can also dive on prey from the air. Due to Hawaii having few native land mammals (The Hawaiian Hoary bat is Hawaii's only native terrestrial mammal), its original diet presumably consisted mainly of smaller birds such as the flightless ducks and rails that once inhabited Hawaii. Today it feeds largely on introduced animals such as rats, lizards, and game birds, as well as invertebrates such as insects. It will also feed on the Hawaiian crow, a Hawaiian bird which is extinct in the wild. They are opportunistic predators and are versatile in their feeding habits. They have a shrill and high-pitched call much like their Hawaiian name: "eeeh-oh." They are very noisy during the breeding season. ʻIo are strong fliers.
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