|Listed||March 11, 1967|
|Family||Accipitriidae (Hawks and Eagles)|
|Description||Bird of prey; dark phase, entirely dark brown; light phase, dark brown with white underparts.|
|Food||Birds, small mammals.|
|Reproduction||Clutch of one egg.|
|Threats||Nest disturbance, habitat loss.|
The Hawaiian hawk, Buteo solitarius, is a broad-winged raptor whose females average 18 in (45.7 cm) in body length and whose males average 16 in (40.6 cm). This hawk, whose Hawaiian common name is the io, has light and dark color phases that occur in about equal numbers. Dark phase adults are dark brown all over, appearing black in the field. Immature hawks have a tawny mottling on back and breast. Light phase adults have a dark brown head and a brown mottled back; the chest and belly are white with brown flecking on the margin. Light phase immatures are brown-bodied with a buff white head and mottled chest. Immatures of both phases have bluish green ceres (the membrane at base of upper beak), legs, and feet.
The Hawaiian hawk is a strong flier and often soars on thermal currents above the slopes of Mauna Loa and Mauna Kea volcanoes. When hunting, it prefers to perch in a tree and swoop down on rodents, other small animals, and birds. The Hawaiian hawk vigorously defends its nest and will attack any other hawk, owl, or even human that ventures too near. A mated pair tends to use the same nest year after year, adding to it each new season until it grows as large as 40 in (101.6 cm) across and 30 in (76.2 cm) deep. Juveniles move into territories of their own in late fall and early winter.
Hawaiian hawks breed at three or four years of age. Birds nest from March through September. The female usually lays a single egg in late April or early May and does most of the incubation. The egg hatches after about 38 days. The female then develops a low tolerance for the male and often keeps him at a distance. For four to five weeks, the male hunts alone and returns to the nest with food. Careful parental care leads to a high fledgling success rate. Chicks fledge at about nine weeks but remain dependent for several months—a long time in comparison with other hawks.
The Hawaiian hawk is the only hawk native to the Hawaiian Islands. It is found from near sea level to an elevation of 8,500 ft (2,590.8 m) and is more abundant in windward than in leeward forests. It avoids dry scrub areas, preferring either open savanna or denser rain forest. The species adapts well to agricultural habitats—papaya groves, macadamia nut orchards, and sugarcane fields—that are bounded by large trees.
Early European explorers found the Hawaiian hawk on the island of Hawaii, where it was common in some localities. It has been sighted occasionally on the islands of Kauai, Oahu, and Maui, but is known to breed only on Hawaii.
The distribution of the Hawaiian hawk has not changed, but its numbers have declined. Within Hawaii Volcanoes National Park, hawk numbers have been recorded for more than 40 years; in 1968, the population reached its low, estimated at several hundred birds. Currently, the population appears stable at about 2,000 birds.
The Hawaiian hawk was once thought to be a guardian spirit that watched over the elder families of Hawaii. Eventually, the hawk itself came to need protection from the drastic decline of its forest habitat. Most lowland forests have been converted for agricultural or urban uses. Non-native plants dominate much of the island below 2,600 ft (792.5 m), while upper-elevation forests have been logged and subsequently converted to pasture.
Field studies carried out in the early 1980s were the first systematic attempt to document the habitat and behavior of the Hawaiian hawk. These studies found that humans were the only true predator of this hawk; for years, illegal shooting took its toll, but this seems to have abated. A more serious problem is harassment of nesting hawks. When nesting birds are disturbed repeatedly, incubation or feeding is disrupted, causing the young to starve or leave the nest prematurely. Frequently disturbed nests are often abandoned by adults.
Conservation and Recovery
Because its population has stabilized, the outlook is bright for the Hawaiian hawk, as long as efforts continue to arrest forest decline and preserve high quality habitat on the island.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
Pacific Remote Islands Ecological Services Field Office
300 Ala Moana Blvd., Room 3-122
P.O. Box 50088
Honolulu, Hawaii 96850
Telephone: (808) 541-1201
Fax: (808) 541-1216
U.S. Fish and Wildlife Service. 1984. "The Hawaiian Hawk Recovery Plan." U. S. Fish and Wildlife Service, Portland.