Hawaiian Hawk

The Hawaiian hawk, or ʻio (Buteo solitarius), is a raptor of majestic bearing, endemic to the lush islands of Hawaiʻi. This bird of prey, with a length of 40 to 46 centimeters, exhibits sexual dimorphism, with the female being the larger sex, averaging 605 grams, while the male is lighter at around 441 grams. The ʻio presents itself in two color phases: a dark phase, with a dark brown head, breast, and underwings, and a light phase, characterized by a dark head with contrasting light breast and underwings. Adult birds boast yellowish feet and legs, while juveniles display a greenish tinge.

Identification Tips

During the breeding season, one can identify one of the pair, possibly the female, by a distinctive yellow forecap, situated just above the upper mandible. This feature, along with the bird's size and color phases, aids in distinguishing the ʻio from other birds of prey.

Habitat

The ʻio is known to favor the native ʻōhiʻa lehua (Metrosideros polymorpha) trees for breeding, a habitat that provides both shelter and sustenance.

Distribution

Once widespread across the Hawaiian archipelago, the ʻio is now restricted to the Big Island, a testament to its adaptability yet also a sign of its vulnerability.

Behaviour

The Hawaiian hawk is a solitary creature, staunchly defending its territory throughout the year. It is a strong flier and an opportunistic predator, versatile in its feeding habits. During the breeding season, the ʻio becomes particularly vocal, its calls echoing through the forests.

Song & calls

The ʻio communicates with a shrill and high-pitched call that mirrors its Hawaiian name: "eeeh-oh," a sound that becomes more prevalent during the breeding season.

Breeding

Breeding occurs from March to September, with the ʻio typically laying a single egg, though clutches of up to three have been recorded. The female predominantly incubates the egg over 38 days, while the male takes on the role of hunter. Post-hatching, the female permits the male to visit only for food delivery. Chicks fledge at seven to eight weeks, with a success rate of fifty to seventy percent for fledging young from the nest.

Diet and Feeding

Originally, the ʻio likely preyed on native birds, but with the introduction of various animals to the islands, its diet has expanded to include rats, lizards, game birds, and invertebrates such as insects. It has also been known to feed on the Hawaiian crow, an unfortunate impediment to the crow's recovery in the wild.

Conservation status

The ʻio was once listed as an endangered species in the United States but was delisted in 2020. However, it remains classified as Near Threatened by the IUCN and considered Vulnerable by NatureServe. Common threats include illegal shootings, habitat degradation, poisoning, vehicle collisions, starvation, and predation.

In Hawaiian culture

The ʻio holds a place of reverence in Hawaiian culture, symbolizing royalty and featuring in the creation chant, the Kumulipo. It is sometimes referred to as ʻiolani, meaning "exalted hawk," a name shared with Kamehameha IV and the ʻIolani Palace.