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

Qualifies for the list as a Red List Species

 

Omao
Photo: Jack Jeffrey

The ‘Oma’o is a medium-sized, fruit-eating thrush that occurs primarily in high-elevation native rainforests on the island of Hawaii. Drab and nondescript, ‘Oma’os are most often located by voice. The ‘Oma’o is still relatively common -- the only one of the Hawaiian thrushes to persist while others exist in very small populations or have become extinct.

 

Despite its healthy numbers, only 30% of this species' former range is intact, and they face the same threats that have decimated other native Hawaiian birds (habitat destruction, introduced predators, and diseases).

 

Formerly common in habitats from 900 to almost 10,000 feet, the 'Oma'o 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 3,900 feet elevation.

 

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 4,900 feet, 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, also pose a continuing threat to Oma'os and other species.

 

The most successful approach to conservation for the O'ma'o has been to buy, protect and manage much of the remaining forested land on the island above 4,900 feet, where disease-carrying mosquitoes become less common. In Hakalau Forest National Wildlife Refuge, created in 1985 to protect ‘Oma'os and other native Hawaiian forest birds, and their habitats, fencing and control programs to exclude or control feral ungulates has allowed native vegetation to return in some areas, although 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 in parks, although control programs continue to be initiated. These actions should increase the production of native birds, but there is some question about the sustainability of such efforts.