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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
2003) and forages over home ranges that average 17.3 ac (VanderWerf 1998, Ralph and Fancy
1994). The Hawai„i creeper most frequently gleans insects, spiders, and other invertebrates from the
branches, trunks, and foliage of live „ōhi„a and koa trees. Beetle larvae make up a large part of its
diet, but no detailed information on prey taken is available (USFWS 2006b).
During the breeding season (typically January-early May) the species‟ home range averages 10-17 ac
and a 33-66 ft elevation. Home range around the nest is defended territory (VanderWerf 1998, Ralph
and Fancy 1994, Lepson et al. 2002). Most nests are open cup structures, but about 15 percent are
placed in cavities or in bark crevices. Hawai„i creepers renest after nest failures, and pairs have been
documented raising two broods in a season. Although nest success of Hawai„i creepers is very low
(11-50 percent), adults have high annual survival (Woodworth et al. 2001).
Hawai„i creepers are susceptible to the same factors that threaten other native Hawaiian forest birds,
including loss and degradation of habitat, predation by mammals, and disease. Hawai„i creeper
population numbers are also limited by their low reproductive potential, high nesting failure, and
possible competition with nonnative bird species.
Logging and grazing has reduced, degraded, and fragmented suitable forest habitats for the Hawai„i
creeper. Habitat fragmentation may be a dispersal barrier preventing or restricting natural
recolonization of the species‟ former range. The Hawai„i creeper‟s absence from habitats below
4,500 ft elevation also suggests that it may be particularly susceptible to mosquito-borne avian
disease (Atkinson et al. 2005).
The productivity of the Hawai„i creeper is also limited by its low reproductive potential and high
rates of nesting failure. The Hawai„i creeper has small clutch sizes, relatively long developmental
periods, and a limited breeding season. Productivity is further reduced by the high rate of nesting
failures, possibly due to the introduction of mammalian nest predators. Hawai„i creepers place their
nests near the main trunks of trees which may facilitate predation by rats (Woodworth et al. 2001). It
has also been suggested that competition with Japanese white-eyes may negatively affect Hawai„i
creepers (Mountainspring and Scott 1985). All these factors contribute to a slow recovery of
populations.
4.4.4 ‘Ō‘ū (Psittirostra psittacea)
The „ō„ū is a heavy-bodied Hawaiian honeycreeper approximately 7 in in total length. The upper
parts are dark olive-green, and the underparts are a lighter olive-green grading to whitish on the
undertail coverts. The wings and tail are a darker brownish olive. „Ō„ū are sexually dichromatic,
males having a bright yellow head that contrasts sharply with the back and breast, and females
having an olive-green head similar in color to the back. Juveniles are similar to the female in color,
but somewhat darker. In both sexes the bill is pale pink to straw-colored, with a hooked, parrot-like
upper mandible. The males are slightly larger than females.
„Ō„ū were found historically on the islands of Hawai„i, Maui, Moloka„i, Lāna„i, O„ahu, and Kaua„i,
and were common throughout their range. Currently, the „ō„ū is one of the rarest birds in Hawai„i and
may possibly be extinct, although past survey efforts have been insufficient to determine its status
(USFWS 2006b). The most recent observations indicate any remaining populations are extremely
localized in occurrence and are restricted to only a fraction of their former range in the mid-elevation
„ōhi„a forest on the islands of Kaua„i and Hawai„i only. During the Hawai„i Forest Bird Surveys from
Chapter 4. Refuge Biology and Habitats 4-25