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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
preferred forage plant species, while „ōhi„a is not favored. The foraging behavior of „akiapōlā„au is
very specialized compared with that of other forest birds, and foraging sites and food may be
limiting. This species rarely takes nectar from flowers, but it recently has been discovered to drink
sap from small wells it drills in the bark of „ōhi„a trees.
Only a few trees in a bird‟s territory are used for this purpose, and they are defended against other
„akiapōlā‟au. On average, sap trees are larger, have thinner bark, greater sap flow, and tend to occur
on convex slopes with more light (Pejchar and Jeffrey 2004).
„Akiapōlā„au often join mixed-species foraging flocks, perhaps to enhance detection of predators. In
montane mesic forests, they most frequently associate with Hawai„i creeper and „ākepa, whereas in
subalpine dry forest they are found with Hawai„i „amakihi and palila. The importance of these flocks
to „akiapōlā„au has not been studied but may prove relevant to the conservation of this species and
the need to maintain intact, functioning ecosystems (USFWS 2006b).
„Akiapōlā„au are limited by habitat loss and degradation, predation, and introduced diseases. Due to
its low reproductive rate, this species may be particularly vulnerable to these threats and slow to
recover. Other factors, such as competition from introduced avian and arthropod insectivores may
also limit the range of the species (USFWS 2006b).
The impact of habitat loss and degradation, particularly in mesic and dry forest, also threaten
„akiapōlā„au. Dry high elevation māmane-naio forest habitat on the slopes of Mauna Kea has been
severely degraded by decades of browsing by goats and sheep. The dispersal behavior of
„akiapōlā„au is poorly known, but habitat fragmentation may isolate the remaining populations,
decrease the effective population size, and hinder recolonization of areas that were formerly
inhabited (USFWS 2006b).
Predation of nests and adults by rats, cats, mongooses, and owls is suspected to have a significant
impact on many native Hawaiian bird species (Atkinson 1977, Smucker et al. 2000, VanderWerf and
Smith 2002). Recent surveys indicate rat densities are high at the HFU, which contains a significant
portion of the largest remaining „akiapōlā„au population (USGS, unpubl.). Juvenile „akiapōlā„au may
be especially vulnerable to predators during the post-fledging period because their loud, persistent
begging call makes them easy to locate (USFWS 2006b).
Most Hawaiian forest birds are susceptible to introduced mosquito-borne diseases, and the
„akiapōlā„au may be limited to its current high-elevation distribution by these diseases (Scott et al.
1986; van Riper et al. 1986; Atkinson et al. 1995, 2005). Despite the availability of apparently
suitable habitat, „akiapōlā„au are absent from most areas below 4,500 ft, where mosquitoes are
common (USFWS 2006b).
4.4.2 Hawai‘i ‘Ākepa (Loxops coccineus coccineus)
The Hawai„i „ākepa is a small sexually dichromatic Hawaiian honeycreeper. Males obtain their
bright orange adult plumage 3 years after hatching (Lepson and Freed 1995). The subadult plumage
is dull brownish-orange, although individual variation is high. Females are grayish green with a
yellow breast band. The lower mandible of the „ākepa is slightly bent to one side which results in the
mandible tips being offset; a characteristic shared with the „akeke„e. The bend can be to the left or
Chapter 4. Refuge Biology and Habitats 4-21