Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Moist air, relatively constant moderate temperature, and lack of light are attributes of these cave
systems. In general, lave tubes can be divided into four zones – entrance, twilight, transition, and true
dark. The entrance zone is the opening of the lava tube and is generally rich in resources. Green
vegetation lessens in the twilight zone where light is reduced. In the transition zone, no light is
present, but surface environmental conditions are not absent. Finally, the true dark zone is
characterized by constant darkness and has steady environmental conditions (Howarth 1973).
4.4 Endangered Hawaiian Forest Birds
Over two-thirds of the remaining native forest birds in Hawai„i are federally listed under the ESA.
The isolation of the Hawaiian Islands has contributed both to the endemism of the forest birds and to
their potential for endangerment. Isolation has made them particularly vulnerable to diseases such as
avian malaria and pox, one of the most critical threats to native forest birds. The endangered species
present in Hakalau Forest NWR include three families of birds: Fringillidae (honeycreepers),
Corvidae (crows) and Accipitridae (hawks). The majority are Hawaiian honeycreepers (Fringillidae:
Drepanidinae) and include the „akiapōlā„au, Hawai„i „ākepa, Hawai„i creeper, and „ō„ū. The „alalā
and „io are the two other species of concern. All species are endemic to the Island of Hawai„i, with
the exception of the „ō„ū, which formerly occurred on all the main Hawaiian Islands but may now be
extinct.
Statewide surveys of the distribution, abundance, and habitat occurrences of native forest birds began
in 1976 (Scott et al. 1986). These efforts were followed up by annual surveys that allow for
monitoring and the examination of trends in forest bird densities over time, particularly of the
endangered Hawaiian forest birds. Long-term data are available for two areas on the Island of
Hawai„i in particular: the North Hāmākua study area and the central windward region of Hawai„i
Island. These two areas are described in detail below.
The North Hāmākua area (160,230 ac) is located on the eastern flank of Mauna Kea, from 1,000-
8,000 ft elevation (Figure 4-4). This area includes the HFU and surrounding public and private lands.
The study area is steeply dissected by ridges and erosion gullies, with frequent major tree falls (Camp
et al. 2003).
Most surveys within the North Hāmākua study area were conducted in the montane forest, which has
a canopy dominated by old growth „ōhi„a and koa. „Ōlapa, pūkiawe, „ōhelo, „ākala, and hāpu„u are
the most common subcanopy trees and shrubs. Vegetation at low elevations (0-1,970 ft) consists of
nonnative trees, shrubs, and grasses in agriculture and urban/exurban settings. Vegetation at middle
elevations (1,970–6,230 ft) is dominated by native „ōhi„a and koa/„ōhi„a forest, whereas the highest
elevations (more than 6,230 ft) are comprised of pasture, subalpine native shrubland, and māmane
and koa woodland. Nonnative plant species may be found throughout parts of the native forest at all
elevations (Camp et al. 2003).
The central windward region of Hawai„i Island includes approximately 166,300 ac of mid- to highelevation
rainforest on the windward slopes of Mauna Loa Volcano, between 2,300-6,890 ft. It was
divided into four study areas: Kūlani-Keauhou, „Ōla„a, Mauna Loa Strip, and East Rift (Gorresen et
al. 2005).
4-14 Chapter 4. Refuge Biology and Habitats