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

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
1976-1981, „ō„ū were detected on the eastern slopes of Mauna Kea and Mauna Loa on Hawai„i
Island and in the Alaka„i Wilderness Preserve on Kaua„i. Population estimates during the Hawai„i
Forest Bird Survey in the late 1970s indicated 400 ± 300 (95 percent CI) birds on the Island of
Hawai„i and 3 ± 6 (95 percent CI) birds on Kaua„i (Scott et al. 1986). More recent surveys have
failed to detect any „ō„ū on either island, although occasional unconfirmed sightings are reported.
Reexamination of past survey data indicates the level of survey effort has to date been insufficient to
confirm the status of the species (USFWS 2006b).
At the HFU, a few „ō„ū were detected during the 1977 bird survey in the lower reaches of the Refuge
in montane wet „ōhi„a and mesic koa/„ōhi„a forest habitat. Two unconfirmed detections have been
reported since that time, along with a possible sighting in the mid-1990s at Nauhi in the lower
Honohina Tract and a possible audio detection 4-5 years ago in the same area. However, a
subsequent search of the area did not detect the species. „Ō„ū are not present at the KFU.
Historically, „ō„ū were known from a wide range of forests extending from sea level to alpine areas,
but dense „ōhi„a forest with „ie„ie was considered to be preferred habitat (USFWS 2006b, Snetsinger
et al.1998). Although wide elevational movements from the upland māmane forests to lowland
forests to feed on guava and kukui were observed seasonally in the past, recent sightings on Kaua„i
and Hawai„i Island (USFWS, unpubl.) show „ō„ū to be confined to mid-elevation (3,000-5,000 ft
mesic and wet „ōhi„a forests with 47-98 in annual rainfall. In this area, the canopy is dominated by
„ōhi„a 33-82 ft high, with a subcanopy of „ie„ie, hāpu„u, „ōlapa, kāwa„u, kōlea, and pilo. These
elevations are well within the mosquito zone where most native forest birds have been extirpated by
mosquito-borne avian malaria and avian pox (Scott et al. 1986).
Collectors in the late 1800s noted that „ō„ū fed mainly on the large inflorescences of „ie„ie, were fond
of the yellow fruits of arboreal Clermontia species, and took fruits from many other native trees
including „ōlapa, māmaki, kāwa„u, alani, and probably „ohe„ohe and „ōhi„a ha. „Ō„ū were also
recorded to feed on young koa leaves, nectar, and on nonnative fruits such as guava, mountain apple,
banana, peach, and mulberry. They have also been observed to forage extensively in kukui; however,
it is unclear if they seek nectar, insects, or husks of the oily nuts (Scott et al. 1986, Snetsinger et al.
1998, USFWS 2006b). „Ō„ū were also noted to feed on caterpillars (Geometridae), and feed them to
young during the summer months in the Ka„ū/Kīlauea area. Nesting of the „ō„ū has never been
described and little is known of its breeding habits.
„Ō„ū are threatened by the loss and degradation of habitat, the loss of food resources, disease and
predation by mammals as well as natural disasters. Modification and loss of habitat have played a
significant role in the decline of the „ō„ū. Forest degradation by ungulates has reduced or eliminated
forest habitat and food resources by converting vast areas of koa and „ōhi„a forest to pasturelands.
Pigs have caused degradation of the understory in wet forests, destroyed food plants such as „ie„ie
and Clermontia species, and have created mosquito breeding sites (USFWS 2006b).
Predation by rats on eggs and cats and rats on young and adults has contributed to the decline of
many forest birds, probably including the „ō„ū. Herbivory by introduced black rats on the fruits and
flowers of „ie„ie and other native fruiting plants also may have reduced food resources for native
birds in forests throughout Hawai„i (USFWS 2006b).
In addition, recent natural disasters may have affected some of the last remaining „ō„ū populations.
On the island of Hawai„i, a large portion of the Upper Waiākea Forest Reserve (a location of some of
4-26 Chapter 4. Refuge Biology and Habitats