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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Hawai„i „ākepa occur in „ōhi„a and koa/„ōhi„a forests above 4,300 ft (USFWS 2006b). The species
feeds mainly on „ōhi„a leaf clusters, but also on koa leaves and seed pods, where it uses its bill to pry
open leaf and flower buds in search of small arthropods. Birds also have been seen foraging
occasionally in the leaves of naio, „a„ali„i, pūkiawe, pilo, „ōhelo, and „ākala. The Hawai„i „ākepa
feeds primarily on small insects, spiders, and caterpillars throughout the year. It rarely feeds on
nectar (Fretz 2000). Both adults and juveniles frequently join interspecific foraging flocks with other
Hawaiian honeycreepers, particularly Hawai„i creepers, and also „akiapōlā„au, Hawai„i „amakihi,
„i„iwi, and „apapane.
Hawai„i „ākepa breed from early March-May (Lepson et al. 1997). This species is an obligate cavity
nester, with most nests placed in natural cavities found in old-growth „ōhi„a and koa trees.
Consequently, their density depends in part on the density of large trees, because only large trees
provide the cavities required for nesting (Hart 2000, 2001; Freed 2001). The average size of trees
used for nesting is 3.3 ft in diameter at breast height (Freed 2001). „Ōhi„a appear to be more
important to „ākepa than koa. Large „ōhi„a trees provide both cavities for nest-sites and the preferred
foraging substrate, whereas large koa trees provide mainly cavities (Freed 2001). The greater
importance of „ōhi„a is also supported by „ākepa densities because the highest density of Hawai„i
„ākepa on Mauna Loa, in the Ka‟ū Forest Reserve, is in an area without koa (Scott et al. 1986).
Breeding densities at HFU appear to be limited by the availability of nest sites (Hart 2000), and the
population may be at or near carrying capacity with respect to food availability (Fretz 2000).
Hawai„i „ākepa are likely susceptible to the same factors that threaten other native Hawaiian forest
birds, including: loss and degradation of habitat, predation by mammals, and disease (Mitchell et al.
2005, USFWS 2006b). Hawai„i „ākepa are especially sensitive to the loss of old growth forest due to
their dependence on large trees with cavities for nesting (Freed 2001). The clearing of forest by
logging and ranching has greatly reduced the amount of suitable habitat for Hawai„i „ākepa and other
forest birds. Logging and ranching has also resulted in the fragmentation of the remaining forest
habitat. It was previously thought that areas of highest „ākepa density with trees large enough to
provide nest sites were falling at a rate of 13 trees per mi 2 per year at HFU and that reduction of nest
sites in high-density areas was a major threat. New data by Hart et al. shows that the forest is
recovering, that large tree loss may not be a limiting factor currently, and that the forest will provide
nest sites in the future.
It is possible that the increased light under which „ōhi„a seedlings are germinating is producing trees
with an almost exclusively sympodial (multi-trunked) growth form, which typically do not produce
cavities suitable for Hawai„i „ākepa nests, although not enough data is available to say this
definitively. The „ōhi„a trees used as nest sites by the birds are almost exclusively monopodial
(straight and single-trunked) in form (Freed 2001).
Hawai„i „ākepa are also threatened by avian diseases. The species is not found below 4,300 ft,
presumably because of the distribution of the introduced mosquito that transmits avian malaria and
avian pox (van Riper et al. 1986, 2002). Furthermore, the cavity nests of the Hawai„i „ākepa may be
vulnerable to rat predation. However, nest success is high at Pua „Ākala in the HFU, where rat
densities are high (Mitchell et al. 2005).
Forest bird issues including potential competition between the invasive Japanese white- eye and the
„ākepa, as well as „ākepa status and a debate over survey methodology and data analysis in the
scientific community have been addressed in recent years through the Service‟s peer review
Chapter 4. Refuge Biology and Habitats 4-23