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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
dependent on „ōhi„a for food and nesting. „I„iwi spend up to 80-90 percent of their time foraging on
„ōhi„a for nectar and insects. As they are primarily nectarivorous; the nectar of „ōhi„a and māmane
make up a major portion of their diet. The species also feeds on foliage insects and spiders (Ralph
and Fancy 1995). Other plant species used for foraging on nectar and insects include koa, naio, kōlea,
„ākala, alani, kanawao, koki„o ke„oke„o, and native lobelioids. Banana poka nectar is a major food
source in some areas (Fancy and Ralph 1998).
Breeding season on Hawai„i Island begins October-November, with peak breeding between
February-June. Breeding coincides with seasonal availability of „ōhi„a nectar. Both sexes defend
small nesting territories and may sometimes defend individual „ōhi„a trees as nectar resources. While
„i„iwi are dependent on „ōhi„a for feeding and nesting, „i„iwi also serve as important pollinators of
„ōhi„a and native lobeliods.
„I‟iwi distribution range is restricted mostly to elevations greater than 4,100 ft because of loss and
destruction of native forests and presence of cold-intolerant Culex mosquitoes that transmit avian
diseases at lower elevations (Scott et al. 1986, van Riper et al. 1986, Atkinson et al. 1995). However,
„i„iwi are known to migrate to lower elevations during the summer. „I„iwi are very susceptible to
avian malaria and avian pox. Mortality of experimentally infected „i„iwi is high, with estimates at
90 percent (Atkinson et al. 1995). Individuals infected with pox also are more likely to be infected
with malaria. The KFU has a high prevalence of malaria and avian pox, and data shows that few
„i„iwi survive the exposure (Atkinson et al. 2005). The presence of pigs in the KFU and limited areas
of the HFU may also spread malaria as the compaction of soils and felling and hollowing of tree
ferns by pigs create favored breeding sites for Culex mosquitoes.„I„iwi fledglings may also be
susceptible to predation by rats and cats found in the units (Mitchell et al. 2005).
4.5.2 Common ‘Amakihi (Hemignathus virens)
Male common „amakihi are bright yellow-green with black lores. Females are generally similar, but
duller. All „amakihi have decurved bills. The immatures are drab gray and may lack dark lores and
some have faint wingbars.
The Hawaiian Forest Bird Survey (1976-1983) estimated the Hawai„i „amakihi population at
870,000 ± 5,612 (95 percent CI) individuals on the Island of Hawai„i, 44,000 ± 1,786 (95 percent CI)
birds on east Maui, 3,000 ± 408 (95 percent CI) on west Maui, and 1,800 ± 357 (95 percent CI)
individuals on Moloka„i. Populations on the islands of Hawai„i and Maui are probably stable; the
Moloka„i population is probably declining (Mitchell et al. 2005).
A population of 200,760 + 990 (SE) common „amakihi was estimated to occur within the north
Hāmākua study area, of which 51,600 birds (26 percent) were predicted to occur within the HFU
(Camp et al. 2003). The mean density of common „amakihi for the 14-year study period of surveys
within the HFU (1987-2000) was 5.2 birds per acre (SD = 7.63). Common „amakihi populations
within and near the HFU did not show a significantly positive or negative trend in density from 1987-
2000. However, „amakihi density increased over the 24-year study period (1977-2000). From 1999-
2007, the population of common „amakihi at the HFU was also stable or increasing. The population
was estimated to potentially have increased at a mean rate of 2.5 percent per year (95 percent CI -7.9-
12.9 percent) (Hawai„i Forest Database 2005). Common „amakihi demonstrated low within-year but
moderately high between-year variability in density.
Chapter 4. Refuge Biology and Habitats 4-33