Data Zone
Justification of Red List category
This species has a restricted range on one island where habitat degradation is ongoing. It is therefore assessed as Near Threatened.
Population justification
The population was estimated to total c.170,000 birds based on surveys in 1976-1979 (Scott et al. 1986), including 56,000 ± 3,000 in Ka'ü, on southern slope of Mauna Loa Volcano, which may be separate from the 113,000 ± 3,000 in remainder of range because of deforested rangeland in Kapäpala tract (Scott et al. 1986). 13,620 (95% CI: 9,581–19,645) individuals are estimated to occur in Hakalau Forest National Wildlife Refuge (Kendall et al. 2022). The global population estimate is roughly equivalent to 110,000 mature individuals overall.
Trend justification
The species faces stresses from habitat degradation, disease and predation from introduced species; however, at lower elevations there is strong selection pressure for disease resistance, and lineages exhibiting these traits may be expanding (Ralph and Fancy 1994; Wakelee and Fancy 1999, 2020). There is no information on trend of individuals found above the tree line and no changes in distribution have been detected since the late 1970s (Wakelee and Fancy 2020). A recent analysis of annual population density estimates in the Hakalau Forest National Wildlife Refuge, which supports 8% of the global population, showed an overall downwards trend in closed forest in the time period 1999-2019 and an increasing trend in the most recent decade 2010-2019 (Kendall et al. 2022). The current overall population trend for this species is unknown.
Myadestes obscurus is endemic to Hawai'i in the Hawaiian Islands (USA) where it formerly occurred almost throughout the island. It is now restricted to the southern and eastern slopes of the island, largely above 1,000 m, c.25-30% of its former range (Scott et al. 1986, Wakelee and Fancy 1999). Here the species is encountered regularly in forests with some native tree component (R. Camp in litt. 2007). The population may be divided by the deforested rangeland of the Kapapala Tract, and a third possibly disjunct population exists above 2000 m on Mauna Loa (Scott et al. 1986, Pratt et al. 1987), where it is widespread in suitable habitat (T. Pratt in litt. 2007).
It favours mesic and wet native forests, but is also found at much lower densities in scrub and savanna habitats, especially where `ohi`a and koa trees are present. It occurs in some areas where introduced plants dominate, but is absent in others, its range being negatively correlated with the widespread exotic banana poka. It feeds primarily on fruit and berries, but also on insects (especially caterpillars), snails and fleshy flower bracts of the `ie`ie vine (Berger 1972, Scott et al. 1986). The species plays an important role as a seed disperser of native plants and its absence from areas where it once occurred may be limiting the regeneration of native understorey (L. Pejchar in litt. 2007).
Habitat clearance for development, firewood, timber, croplands and pasture inevitably caused considerable contractions in this species' range, with most forests below 800 m having been converted to agricultural or urban uses. The spread of feral ungulates into native forests has caused habitat degradation, and in some areas non-native plants have replaced the natural habitat (USFWS and Hawai`i Forest Bird Recovery Team 1982, Loope and Medeiros 1995). Feral pigs Sus domesticus are particularly disruptive and facilitate the spread of introduced, disease-carrying mosquitoes (USFWS and Hawai`i Forest Bird Recovery Team 1982, Anderson and Stone 1993). Pigs also damage and destroy understorey plants that provide the fruit resources that the species depends upon (L. Pejchar in litt. 2007). Current avian predators include Hawaiian Hawk Buteo solitarius, Hawaiian Short-eared Owl Asio flammeus sandwichensis and Barn Owl Tyto alba. Introduced mammalian predators including rats Rattus spp., cats Felis catus and mongooses Herpestes auropunctatus are a further significant limiting factor (Wakelee and Fancy 1999). Avian malaria and avian poxvirus have likely contributed to the disappearance of this species from areas of its former range and continue to be threats, although prevalence of avian malaria is low and the persistence of some lower elevation populations suggests that some individuals are resistant to or at least tolerant of current strains of avian pox and malaria (Wakelee and Fancy 2020). Ectoparasites, particularly chewing lice, are thought to be an additional threat (Freed et al. 2008).
Conservation Actions Underway
It occurs in a number of important and well managed protected areas, such as the Hawai'i Volcanoes National Park (Wakelee and Fancy 1999). During the 1990s, efforts were made to reduce the feral pig population by Hawaiian conservation authorities and private landowners (Anderson and Stone 1993). Reforestation of upland pastures is ongoing (T. Pratt in litt. 2007). There is considerable interest in re-establishing the species on the western slopes of the island (T. Pratt in litt. 2007). Large areas have been fenced to exclude feral ungulates, and control and removal is ongoing (Wakelee and Fancy 2020). Control of alien mammalian predators such as rats and feral cats has been attempted in only a few areas using ground-based control methods (Wakelee and Fancy 2020). Larger-scale efforts involving aerial drops of toxicants to control rodents are being planned (Wakelee and Fancy 2020).
18 cm. Small, dull-coloured thrush. Grey-brown above fading to grey on forehead, grey below except for buff undertail-coverts. Juvenile dark brown above heavily spotted with buff, buffy below heavily scalloped with dark brown. Similar spp. Introduced Chinese Hwamei Garrulax canorus brighter cinnamon-brown with yellow bill. Voice Song a jerky melody of liquid notes whip-per-weeo-whip-per-weet or an ascending series of twangy notes. Call a cat-like rasp, frog-like croak, or higher "police whistle". Hints Most accessible localities are Hawaii Volcanoes National Park and forest patches along Saddle Road.
Text account compilers
Vine, J.
Contributors
Camp, R., Pejchar, L. & Pratt, T.
Recommended citation
BirdLife International (2024) Species factsheet: Omao Myadestes obscurus. Downloaded from
https://datazone.birdlife.org/species/factsheet/omao-myadestes-obscurus on 24/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/12/2024.