The Hawaiian hawk, also called the io, is the only hawk native to the Hawaiian Islands. The color of its plumage (covering of feathers) varies from dark brown to tawny brown to almost white.
Dark spots mark its chest, belly, and the undersides of its wings. An average adult Hawaiian hawk measures 16 to 18 inches (41 to 46 centimeters) long. Females are slightly larger than males.
The Hawaiian hawk is an agile flier, performing acrobatic movements at great heights. It often flies on thermal, or warm, air currents above volcanoes. To hunt, the bird generally perches in a tree before swooping down on its prey. Large insects and birds originally made up its diet. It now feeds on rodents that human settlers have introduced to its habitat.
A male–female pair builds a nest fairly low in a tree and then reuses it each year, adding sticks and branches. The nest can become quite large, up to 40 inches (102 centimeters) wide and 30 inches (76 centimeters) deep.
Nesting begins in March, with the female laying a single egg in April or May. While she incubates (sits on or broods) the egg for 38 days, the male hunts and gathers food. The young hawk fledges (develops flying feathers) after eight or nine weeks, but remains dependent on its parents for several months.
Habitat and current distribution
The Hawaiian hawk breeds only on the island of Hawaii, but ranges as far as the islands of Maui and Oahu. It is found from sea level to 8,500 feet (2,590 meters), but generally prefers elevations from 2,000 to 5,000 feet (610 to 1,524 meters). The bird adapts to various habitats, including light woodland, forests, and farmland or other cultivated areas bordered by trees.
Biologists (people who study living organisms) estimate the Hawaiian hawk population to be about 2,000.
History and conservation measures
In the mid–1970s, biologists estimated that only a few hundred Hawaiian hawks existed. Since then, a number of protected areas for the hawks and other endangered forest birds have been set aside. Their recovery has been substantial. In 1993 the U.S. Fish and Wildlife Service proposed to reclassify the Hawaiian hawk from endangered to threatened.
Again, in May 1998, U.S. Interior Secretary Bruce Babbitt included the Hawaiian hawk on a list of 29 species whose status on the Endangered Species List would be changed. The matter remained pending well into the twenty–first century.