The Ka`u Forest Important Bird Area is located on the southeastern flank of Mauna Loa volcano on the island of Hawai`i. It includes about 44,146 hectares of native forest, woodland, and shrubland extending from about 600 to 2550 meters (2000 to 8400 feet) elevation. The State of Hawai`i?s Ka`u Forest Reserve comprises the majority of the area, but some important habitat for native forest birds above 1500 meters elevation is owned and managed by Hawaii Volcanoes National Park. The area also includes portions of the State of Hawai`i?s Kapapala Forest Reserve and Kapapala Cooperative Game Management Area. Several smaller sections are owned and managed by The Nature Conservancy of Hawaii and Kamehameha Schools. The terrain consists of gentle to moderate slopes and rocky gulches cut by streams, punctuated by steep, vegetated cinder cones in some areas. Most of the lower and middle elevations are covered in dense rainforest or mesic woodland. Rainfall is highest in the center of the area, peaking at over three meters per year from 900-1000 meters elevation, declining toward the east and west. The upper elevations become increasingly dry and rocky toward the summit of volcanically active Mauna Loa. The lower forest boundary is an abrupt, unnatural edge created by forest clearing for sugar cane plantations and cattle ranching.
The Ka`u forest area supports one of the most important remaining concentrations of endemic Hawaiian birds, including populations of four species that are endemic to Hawaii Island and listed under the U.S. Endangered Species Act, the `Akiapola`au (Hemignathus munroi), Hawai`i Creeper (Oreomystis mana), Hawai`i `Akepa (Loxops coccineus), and `Io or Hawaiian Hawk (Buteo solitarius). The populations of `Akiapola`au, Hawai`i Creeper, and `Akepa are the second largest for these species, after those in the area centered around Hakalau Forest National Wildlife Refuge. The area also supports relatively large populations of three other endemic forest birds of global conservation concern, the `I`iwi (Vestiaria coccinea), Oma`o (Myadestes obscurus), and Hawaii `Elepaio (Chasiempis s. sandwichensis), and two more endemic forest birds that are more common but have globally restricted ranges, the `Apapane (Himatione sanguinea) and Hawai`i `Amakihi (Hemignathus virens). The Pueo (Asio flammeus sandwichensis), a subspecies of the Short-eared Owl endemic to the Hawaiian Islands, occurs throughout the area. A small number of endangered Nene or Hawaiian Goose (Branta sandvicensis) have been reintroduced in the southwestern portion of the Ka`u area. Small numbers of the Hawaiian Petrel (Pterodroma sandwichensis), another endangered species endemic to the Hawaiian Islands, are known to transit the area while commuting to nesting areas higher on Mauna Loa, and it is possible that a few petrels nest along the top margin of the Ka`u forest area. The Ka`u forest is one of the top sites being considered for reintroduction of captive-bred `Alala or Hawaiian Crows (Corvus hawaiiensis), which are currently extirpated in the wild.
Non-native mammals are the most serious threat to the Ka`u forest and the birds it supports. Non-native ungulates, particularly feral cattle and pigs and mouflon sheep have destroyed much of the understory in some areas and prevented recruitment of trees. Mouflon were particularly abundant in the former Kahuku Ranch, where they were introduced for hunting, but numbers have been reduced since the area was acquired by the National Park Service and fencing and eradication efforts were begun. Feral pigs occur throughout the area and degrade habitat by rooting in the understory, spreading the seeds of invasive alien plants, and creating breeding sites for non-native mosquitoes that carry avian malaria and avian pox virus. Hollowed trunks of tree ferns toppled by feral pigs are the primary breeding site for mosquitoes in some areas. Abundance of endemic forest birds is higher above 1500 meters elevation, and `Akiapola`au, Hawaii Creeper, and `Akepa occur only above 1500 meters, because mosquito larvae and the malaria parasite cannot tolerate colder temperatures. Nectarivorous species like `I`iwi and `Apapane move altitudinally in search of flowering trees and can be exposed to mosquito-borne diseases when they descend. Nest predation by non-native mammals is also a serious threat. Forest bird nests probably are depredated most often by black rats, which are good climbers. For ground-nesting Nene and Hawaiian Petrel, mongoose and feral cats are the most serious predators. Feral cats also carry Toxoplasmosis, which can be fatal to `Alala. Invasive alien plants are a serious threat and degrade habitat quality by displacing native plant species. Plantations of non-native trees on the southern edge, particularly Eucalyptus and silk oak (Grevillea robusta), threaten to spread into adjacent native forest areas. Other serious invasive plants are Christmasberry (Schinus terebinthifolius), an aggressive weedy shrub that can dominate mesic and drier areas, and strawberry guava.
The majority of the Ka`u Forest Important Bird Area is owned by the State of Hawai`i. Most of this land comprises the Ka`u and Kapapala Forest Reserves. A small portion of the State land is leased to a private rancher and is managed as the Kapapala Cooperative Game Management Area. The western end and much of the northern edge are federally owned and are part of Hawai`i Volcanoes National Park. Several small parcels along the southern edge of the area are owned by The Nature Conservancy of Hawai`i and Kamehameha Schools.
The Ka`u forest area is located between 600 and 2550 meters elevation on the southeastern slope of Mauna Loa Volcano. Forest bird habitat in the area consists of four general types: 1) montane wet and mesic forest, 2) forested pasture, 3) subalpine woodland, and 4) subalpine shrubland. The higher elevations also include some bare lava from recent volcanic eruptions, particularly in the northwestern corner near the southwest rift zone of Mauna Loa. Rainfall is highest in the middle elevations, peaking at over three meters per year around 900 meters elevation, and decreasing toward the coast and the barren summit of Mauna Loa. Rainfall is also generally higher in the western portion and becomes progressively lower toward the east. The wet and mesic native forest is composed primarily of `ohi`a (Metrosideros polymorpha) associations that include varying amounts of koa (Acacia koa), `olapa (Cheirodendron trigynum), and understory components such as tree fern (Cibotium glaucum) and `uluhe fern (Dicranopteris linearis). Forested pasture is patchily distributed around the margins of the area, with concentrations on the western end in the Kahuku Ranch section of Hawai`i Volcanoes National Park and the eastern end in the Kapapala Forest Reserve and Game Management Area. Canopy cover and understory density have been considerably reduced in portions of these areas by up to 150 years of ranching. The dry subalpine woodland and shrubland at the upper edge of the area is dominated by `ohi`a, pukiawe (Styphelia tameiamaeiae), `ohelo (Vaccinium spp.), and other shrub species. The southern boundary is an abrupt, unnatural edge created by clearing of forest for agriculture, silviculture, and cattle ranching. Some patches along the lower boundary and in the western portion of the area consist of fallow sugar cane plantations, open pasture, and exotic tree plantations.
Almost all of the land comprising the Ka`u Forest Important Bird Area is now used for conservation purposes. However, some of the lands that now comprise the lower elevations of Hawai`i Volcanoes National Park and the Ka`u and Kapapala State Forest Reserves were formerly used for agricultural purposes, primarily cattle ranching and sugar cane production. Similarly, several small parcels owned by The Nature Conservancy of Hawai`i and Kamehameha Schools are zoned in part for agriculture and were used for agricultural purposes in the past. All of the Ka`u and Kapapala Forest Reserves are open to public hunting of non-native game animals and non-native game birds. The Kapapala Cooperative Game Management Area is used primarily for private cattle ranching but is also open to public hunting of non-native game birds. A portion of the Kapapala Cooperative Game Management Area was removed from lease in 2005 and set aside as the Kapapala Koa Canoe Forest Management Area, which may be used for selective logging of a small number of large, straight-trunked koa trees for construction of traditional Hawaiian sailing canoes.