WatchList Species Account for ‘Oma’o (Myadestes obscurus)

Qualifies for the list as a Red List Species

Photo: © Jack Jeffrey

Found only on the island of Hawaii, the ‘Oma’o is a medium-sized, fruit-eating thrush that occurs primarily in high-elevation native rainforests. Drab and nondescript, ‘Oma’os are most often located by voice. Still relatively common, the ‘Oma’o is the only one of the Hawaiian thrushes to persist while the others exist in very small populations or have become extinct. Despite its healthy population numbers, only 30% of this species' former range remains intact, and ‘Oma'os face the same threats that have decimated other native Hawaiian bird populations (habitat destruction, introduced predators, and diseases). Formerly common in habitats from 300 to 3,000 m, it is currently found only on the eastern and southern slopes of the island. Its numbers appear to be stable in areas with high-quality habitat, and populations might be increasing in sites below 1,200 meters of elevation.

Primarily frugivorous throughout the year, the bird eats both native and introduced fruits, but also feeds on invertebrates, including snails. It lives mainly in wet native 'ohi'a and mixed 'ohi'a /koa forests at the higher elevations. There is evidence that the ‘Oma'o has developed partial resistance to, or at least tolerance for, current strains of avian pox virus and malaria. This may account for this species' continued persistence where other species have disappeared. Despite this suspected tolerance, Oma'os still fare best above 1,500 meters, where disease-carrying mosquitoes are scarce. The introduction of cold-tolerant mosquitoes, along with new avian diseases, is a potential major threat to Oma'os and other forest-dwelling Hawaiian birds. Feral pigs in native forests create favorable conditions for mosquito breeding, in addition to the devastation the pigs cause to native understory plants. The presence in native forests of non-native terrestrial predators, such as rats and feral cats, represents a continuing threat to Oma'os and other species.

In terms of conservation of the species, the most successful approach has been to buy, protect and manage much of the remaining forested land on the island above 1,500 m, where disease-carrying mosquitoes become less common. Several parks, refuges and natural areas have been established with the primary goal of conserving native plants and animals. For example, Hakalau Forest National Wildlife Refuge was created in 1985 to protect ‘Oma'os, other native Hawaiian forest birds, and their habitats. Large areas have been fenced to exclude or control feral ungulates, and a control program has been initiated to control or eradicate feral pigs and to control or remove other ungulates that have degraded native forests. Although this has allowed native vegetation to return in some areas there is as yet no evidence that this has resulted in increased bird numbers. Invasive weeds and introduced predators continue to be a major problem, although control of rats and feral cats has also been initiated. This should increase the production of native birds, but there is some question about the sustainability of such efforts.