Endangered Species in the Pacific Islands
Hawaiian Hawk / Buteo solitarius / ‘Io
||This graceful bird of prey measures 16 to 18 inches in length, the female being larger. 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 immatures.
|Hawaiian hawk - © Jack Jeffrey
Habitat & Behavior:
Conversion of native forest to residential, large-scale agriculture, exotic forestry, and to business and industrial areas have been and will continue to have the greatest negative impact on this species. Hawaiian hawks can be seen souring over or foraging in these changed areas but they typically do not nest in them. These areas may also be a source of high mortality, especially for young birds. Shooting, vehicle collisions; poisoning; starvation; and predation by dogs, cats, and mongoose are documented sources of mortality.
The ‘io is endemic to Hawai‘i and was a symbol of royalty in Hawaiian legend. The ‘io is also the only hawk today native to Hawai‘i. They only breed on the Big Island but have been occasionally seen on Maui, O‘ahu, and Kaua‘i. Fossil records indicate that this hawk may also been established on Moloka‘i and Kaua‘i. They depend on native forest for nesting, but are able to use a broad range of habitats for foraging, including papaya and macadamia nut orchards, as well as forests dominated by native and introduced vegetation, from sea level to 6,500 feet elevation.
This mostly solitary hawk remains in and defends its territories year round. They nest from March through September, and usually lay only one egg. 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.
The ‘io usually hunts from a stationary position, but can also dive on prey from the air. It feeds on rodents, insects, small birds, and some game birds. 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 known to be very noisy during the breading season. ‘Io are strong fliers.
Past & Present:
The earliest record of the ‘io was on Kaua‘i by a naturalist working for Captain James Cook. This hawk was not recorded again until the U.S. Exploring Expedition of 1840-41. Based on six months of survey, it was concluded that the ‘io occurred only on the Big Island. Historical records show that the bird lived within the same range of elevations as today, however, there is not much historical data on population size that can be used as a baseline to compare with current estimates. There are an estimated 3,000 ‘io, based on a 2007 census.
The ‘io was listed as an endangered species in 1967 under the Federal Endangered Species Act because little was known about this species and raptors worldwide were experiencing significant declines. A recovery plan for the ‘io was published in 1984 which presented research needs for the species and criteria for evaluating recovery of the bird.
The U.S. Fish and Wildlife Service (Service) conducted an extensive Hawai‘i Forest Bird Survey from 1976-1979. This survey has given scientists a wealth of data to further study and understand the many species of birds that live here.
A Service-funded study focusing on breeding success, nesting habitat, survival, and population estimation was completed in 2000. The study looked at parasites in the nest, environmental contaminants in eggs from failed nests, and whether the hawk population is infected with avian malaria and toxoplasmosis.
Hawaiian Hawk Fact Sheet
Draft Post-Delisting Monitoring Plan