Observations on Distribution, Diet, and Breeding of the Hawaiian Thrush

Although hosting a variety of endemic birds, the Hawaiian Islands have only two native species of the Thrush family (Turdidae).The island of Hawaii supports only the larger species, the Omao (Phaeornis obscurus ob-SCUTUS) .Working in native forests throughout the past seven years, we have observed Omao many times, and because so little is known of the bird, we have compiled our data to elucidate present-day distribution, breeding habits, and diet of the species.DISTRIBUTION The Omao is presently believed to be extinct on Oahu and Lanai, much reduced on Molokai (Scott et al. 1977) and Kauai (Berger 1972), but still common on Hawaii.There has been, however, some reduction in its range on Hawaii (Fig. 1).We have failed to find the species in the Kohala Mountains or in the Kona area, although Perkins ( 1903) recorded it as quite abundant in Kohala; Wilson and Evans (1890-1899), Henshaw ( 1902), and Munro ( 1944) all cited the Omao as common in Kona.In a recent avian survey of the South Kona Forest Reserve, C. Morgan (pers.comm.) also failed to find any.Omao are still abundant in the windward (e.g., northeastern) forests on Hawaii, and have a continuous distribution from Kahuku Ranch, through Hawaii Volcanoes National Park, to the northern reaches of the Hilo Forest Reserve ( Fig. 1) .The elevational distribution of the Omao is quite wide when compared to ranges of other extant native passerines, although its range has decreased.Henshaw (1902) found the bird present from 305 m in elevation to the upper forest limits.Today, lowest occurrence in the Kau Forest is 700 m, and in the Puna Forest Reserve approximately 550 m.In the Waiakea forests Omao are found as low as 800 m; throughout the Hilo Forest Reserve the lower elevational limit is approximately 1,000 m.In the latter region, an extensive area of forest die-back appears to limit the birds to the higher elevations.Upper elevational limits are still generally dictated by its habitat, the ohia (Metrosideros collina) and ohia-koa (Acacia koa) forests on both Mauna Loa and Mauna Kea.We have, however, regularly seen Omao in alpine and subalpine scrub habitats on Mauna Loa.Omao populations in these habitat types above the Kau Forest Reserve were continuous with the forest population.However, there are widely scattered sightings of this species as high as 3,500 m on the eastern flank of Mauna Loa (J.Jacobi, pers.comm.).Because these highaltitude birds are so far removed from the nearest forest Omao, it is possible that they constitute distinct populations, although study with banded individuals is needed before this question can be resolved. DIETLittle quantitative data exist on food preferences of the Omao.Henshaw (1902) found that less than five percent of the birds he collected contained insect parts, and that most of the stomachs held only berries.He did find an occasional stomach that had spiders or brown looper caterpillars ( Geometridae) , and also noted one that contained a minute landshell.Omao were known to migrate to parts of the forest which had outbreaks of caterpillars (Perkins 1903).We have observed Omao gleaning for insects on branches and trunks of various tree species, but more frequently on koa and kawau (llex anon&a).Larger trunks appeared to be preferred, and from perches birds often dashed into the air to hawk flying insects.Omao also forage on the ground.These birds appear to eat mostly fruit, including that of kopiko (Psychotria hawai-ien&), kawau, ieie ( Freycinetia arborea), mamaki ( Pipturus albidus) , olopua ( Osmanthus sandwicensis) , olapa (Cheirodendron trigynum) , and pilo ( Coprosmu ernodeoides, C. menziesii, C. montana, C. pubens, C. rhynchocarpa) in its diet (Henshaw 1902, Perkins 1903, Pratt 1971).Our observations indicate that Omao are opportunists, taking seasonal fruits with supplements of various insects (Table 1): In a kipuka (an island of forest in younger vegetation) off the Saddle Road on 9 March 1972, we saw an Omao displacing a smaller individual and then consuming ripe maile ( Alyxia oliuaeformis)