The Hawaiian Hawk (Buteo solitarius), known locally as the ʻIo, is an endemic hawk species found nowhere else in the world. This unique raptor is the sole diurnal bird of prey native to the Hawaiian archipelago and is the focus of conservation efforts.
The Endemic Hawaiian Hawk (‘Io)
The ʻIo is a medium-sized bird, with the overall length of the adult typically measuring between 16 and 18 inches. Like many raptors, the female is noticeably larger than the male, often weighing approximately 25 percent more. This size difference is thought to reduce competition for food resources between the mated pair.
A distinctive feature of the species is the presence of two color phases, or morphs, which can appear in the same population. The dark morph has a body covered in deep dark brown feathers, while the light morph displays a dark head but a much lighter, often whitish, breast and underwings. Adults of both morphs have yellowish feet and legs, whereas juveniles can be distinguished by their greenish-colored legs.
This hawk is an opportunistic feeder whose diet has adapted significantly since the arrival of humans and introduced species. Historically, its prey likely consisted of native birds, as there were almost no native land mammals in the islands. Today, the ʻIo feeds on a variety of introduced animals, including rats, mice, and mongooses, alongside native and non-native birds and insects.
The ʻIo is a territorial species that forms long-term, monogamous pair-bonds. They primarily hunt by perching on a stationary lookout, scanning the ground below before dropping down to capture prey. Nest construction is a lengthy process for the pair, sometimes beginning up to two months before the female lays her clutch.
Geographic Range and Conservation Status
The range of the ʻIo is highly restricted, as it is only known to breed on the Island of Hawaiʻi. Fossil evidence indicates that the species once existed on other islands, including Oʻahu and Molokaʻi, but today, its presence elsewhere is extremely rare. The species can be found across the Big Island, utilizing a wide variety of habitats from sea level up to high elevations.
The hawk is found in native ʻōhiʻa forests, which are preferred for nesting, but it also forages in non-native lowland forests, agricultural fields, and even urbanized areas. The breeding period generally runs from March through September. Nests are typically large, bulky bowls constructed of sticks and lined with fresh leaves, usually placed in a large ʻōhiʻa tree.
The ʻIo was listed as Endangered by the U.S. Fish and Wildlife Service in 1967 but was delisted in 2020 after population estimates showed stable numbers. However, the International Union for Conservation of Nature (IUCN) currently classifies the species as Near Threatened. Major threats include habitat degradation from invasive plants, the spread of ʻōhiʻa death disease, and human-caused fatalities from illegal shooting or vehicle collisions.
Distinguishing the ‘Io from Other Raptors
The ʻIo is the only resident hawk species. The state does host other raptors, such as the Short-eared Owl, locally known as the Pueo, which is the other extant native bird of prey in Hawaii.
The Pueo is a ground-nesting owl that hunts during the day, which can lead to misidentification with a hawk. Additionally, introduced species, such as the barn owl, are now established in the islands. Any hawk-like bird observed in the state is either an ʻIo or a very rare vagrant from the mainland, such as a Red-tailed Hawk.
The islands are geographically isolated. Therefore, if a broad-winged hawk is sighted soaring over any habitat on the Big Island, it is almost certainly the endemic ʻIo. Any hawk sighting on an island other than Hawaiʻi should be treated as an unusual and accidental occurrence.