BIOLOGY OF THE HAWAIIAN HAWK BUTEO SOLITARIUS (REPRODUCTION, FOOD HABITS, BEHAVIOR, MOVEMENTS, TAXONOMY)

We studied the distribution, physical characteristics, habitat, reproductive biology, breeding and foraging behaviors, home range characteristics, and taxonomy of the endangered Hawaiian hawk or 'io (Buteo solitarius) on Hawaii Island from April 1980 through July 1982. The distribution of the 'io is similar to that of 80 or more years ago or more, but its population has probably suffered a long-term decline. Today, the total hawk population is estimated at 1,400 to 2,500 birds.;No differences were found in success of 'io nests in habitats dominated by native (77%) versus exotic (65%) vegetation. Avian malaria, introduced predators, and environmental contaminants were not seriously affecting the 'io population.;'Io have a regular breeding season but do not breed every year. Both sexes assisted with nest building with females and males making 64% and 34% of the trips to the nest with materials, respectively. Male 'io assisted females with incubation. Only females brooded young but males provided most of the food at nests through week 4 of the nestling period.;'Io utilized a wide variety of introduced and native prey items, including 13 species of birds, 5 species of mammals, and 1 insect species. Composition of the diet and feeding rates varied greatly between 'io sexes and among habitats.;Twenty-eight 'io nests were found in a variety of native and exotic habitats. The reported clutch size for the 'io is 2-3 eggs; however, in 30 nesting attempts during 3 nesting seasons there were no indications that more than 1 egg was laid. Incubation lasted approximately 38 days. The nestling period extended for 59 to 63 days. Adult 'io delivered prey to juveniles for 25-37 weeks after fledging.;Home ranges of 8 radio-tagged 'io in 7 territories averaged 447 ha, ranging from 48 to 642 ha. Juvenile 'io dispersed from their parents' home ranges in the 6th month after fledging.;Research and management recommendations for the 'io include: periodic population surveys and monitoring of nesting success, protection and improvement of forest ecosystems, identification and prevention of man-related mortality factors affecting 'io, and development of public education programs about 'io.