The Hawaiian thrushes comprise 5 species in the New World solitaire genus Myadestes and are a unique component of the Hawaiian avifauna distinguished through characters of size, plumage, voice, and behavior. With island-specific forms once found on 6 of the main Hawaiian islands, these moderately differentiated thrushes provide an excellent example of the early stages of speciation. The 5 species currently recognized and the islands on which they have occurred are as follows: Puaiohi (M. palmeri) and Käma‘o on Kaua‘i, ‘Öma‘o on Hawai‘i, Oloma‘o on Maui (James and Olson 1991, S. Olson pers. comm.) and Moloka‘i (M. l. rutha) and on Läna‘i (M. l. lanaiensis), and ‘Ämaui on O‘ahu. All except the Puaiohi will be covered in this account (see Snetsinger et al. 1999 for Puaiohi account). Hawaiian names used on the different islands for these thrushes are thought to be corruptions or variations of ‘Ämaui (Manu a Maui, the bird of the Hawaiian demigod Maui; Munro 1944a). Alternatively, these names may have been derived phonetically from a call note produced by these birds; in the case of the Puaiohi, the Hawaiian name is an onomatopoeia for the species' song.
All Hawaiian Myadestes are characterized by drab olive-brown and gray plumage as adults, making them easily distinguishable from the many brightly colored Hawaiian Honeycreepers (Drepanidinae) among the endemic Hawaiian bird community.
As with all other species in the genus Myadestes, Hawaiian thrushes are prone to long bouts of silent, motionless perching. Hawaiian Myadestes, however, exhibit a unique habit of frequent wing-quivering when perched silently. Although songs are loud, unique in composition, and produced throughout the year, the sedentary habits of these birds result in observers detecting these thrushes by sound more frequently than by sight.
With diets consisting primarily of fruits and supplemented by invertebrates, Hawaiian thrushes have filled a unique niche in the Hawaiian avian community. Both native and introduced fruits are included in their diets, and the birds forage opportunistically for seasonally available food items. Invertebrate prey items include caterpillars (Lepidoptera), spiders (Araneida), beetles (Coleoptera), and land snails (Gastropoda). Of the 2 endemic thrushes on Kaua‘i, the larger Käma‘o is thought to be primarily frugivorous, and the smaller Puaiohi may be better suited for capture of invertebrate prey (Snetsinger et al. 1999).
Breeding activity of the ‘Öma‘o extends from January to November, with nesting peaking from April to July. Biparental care of young and social monogamy are thought to characterize the breeding strategy of these thrushes. Virtually no information exists on the breeding habits of the Käma‘o, Oloma‘o, or ‘Ämaui.
Residents of montane rain forests, Hawaiian thrushes once occupied mesic and wet forest habitats of wide elevational range. However, habitat destruction and the introduction of alien predators and diseases have resulted in large range contractions and, in the case of the ‘Ämaui and Oloma‘o, species extinctions. Remaining populations of the ‘Öma‘o on the island of Hawai‘i, and the Käma‘o on Kaua‘i, are now restricted primarily to forested areas above 1,000 m elevation. The current range of the ‘Öma‘o comprises <30% of its former range, and since the Käma‘o has not been sighted since the early 1990s, its status remains highly uncertain.
Habitat destruction, introduced predators, and diseases have been implicated as significant factors leading to the decline of native thrushes in Hawai‘i. As a result, current conservation priorities include habitat preservation and restoration, predator control, captive propagation, and reintroduction efforts, with an ultimate goal of stabilizing existing populations and preventing further localized extinctions.
Of the endemic Hawaiian Myadestes, the ‘Öma‘o has managed to persist while other thrush species have either disappeared or survive only in small populations. Since the Hawaiian thrushes were little studied before the mid-1990s, almost nothing was learned of the biology of the ‘Ämaui, Oloma‘o, and Käma‘o before their disappearance. Recent studies of the breeding biology, population status, movement patterns, and food habits of the Puaiohi and ‘Öma‘o have greatly increased our understanding of these species. The relatively common ‘Öma‘o is the best studied of the Hawaiian thrushes, and a full description of this species is presented in this account. Information on the nearly extinct Käma‘o, the now-extinct ‘Ämaui, and the Oloma‘o is presented when available. Unless specified with the appropriate species subheadings, information presented is for the ‘Öma‘o.