Small Kauai Thrush

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Small Kauai Thrush

Myadestes palmeri

Status	Endangered
Listed	March 11, 1967
Family	Muscicapidae
Description	Rare thrush, brown above, gray below, white abdomen and eye ring.
Habitat	Stream banks in high elevation forests.
Food	Fruit, insects.
Reproduction	Clutch of two eggs.
Threats	Low numbers, habitat disturbance, disease.
Range	Hawaii

Description

The small Kauai thrush, Myadestes (Phaeornis ) palmeri, is a smaller bird than the large Kauai thrush, averaging about 6.9 in (17.5 cm) in length, and it also has a longer and narrower bill. P. palmeri has dark brown underparts growing darker on the head, grayish underparts becoming white on the abdomen, a white eye-ring or white superciliary line, a brown iris, and flesh-colored legs. The bill is blackish, and the feet are pearly white. The sexes were always considered very similar; however, a female (as determined by a brood patch) was recently differentiated from its mate by having a lighter gray on the throat and breast, as well as by possessing an indistinct dark malar line compared to the male's black malar line. Two nestlings observed in the first nest ever found on May 12, 1981 were almost fully feathered with downy heads. Sooty-gray pin feathers covered their heads, necks, throats, and tails. Most conspicuous were their sooty-gray contour feathers tipped with light brown spots about 0.04 in (0.1 cm) in diameter that covered their backs, breasts, and flanks. The iris was dark brown, the eye-ring tan, the bill yellow, the inside of the mouth a bright orange, and the legs pink.

The young of the small Kauai thrush do not lose their spotted plumage for two seasons; even breeding birds maintain their fledgling plumage. Much of what is known about small Kauai thrush breeding was gleaned from the bodies of a dead male and female with spotted plumage. The ovaries of the female were very much enlarged, a condition suggesting that the birds were either breeding or about to breed; in mid-May all indications pointed to breeding season being imminent. A prolonged nesting-cycle in this species similar to that of the omao, a related species on Hawaii, was suggested by the condition of two birds collected in July 1960. One specimen had large, grey testes that measured 0.27 in (0.7 cm) in diameter; the second specimen had foraged independently of the first in its vermiculated immature plumage. One individual captured in 1965 laid a single egg in the spring of 1968, two eggs in June of 1969, and several eggs at a later date. The ground color of the eggs varied from a very pale greenish-blue to a pale grayish-green. Large reddish-brown splotches and smaller spots were scattered over the entire surface of the shells, but were especially concentrated around the larger end of the eggs.

Little is known about parental care. The nest site of the second nest found was observed for two hours, in which time only the female was seen to feed the nestling. She fed the nestling four times and carried out fecal sacs. The male remained in the area, often giving the single-note alarm call. It was possible that the male did not forage for food or feed the nestling because of the observer's presence. The young are helpless and naked at birth.

Behavior

The small Kauai thrush is a shy, secretive, and nonmigratory bird that mostly remains in the same limited territory throughout the year. Territoriality can range from little more than a strong trill by the male from a high tree top to the buzzing alarm note often heard when the species is first encountered. This bird will move quickly into and through underbrush to stay out of sight. The species is seen in terrestrial areas not considered riparian; most frequently these birds are found near mountain streams heavily covered with various ferns. Only two nests have ever been found. The nest found on May 12, 1981 was located at 5,200 ft (1,585 m) elevation on a streamside cliff in the Alakai Swamp. It was situated in a cavity in the bank 5 ft (1.5 m) above the ground. The earth bank was 19.7 ft (6 m) high, well vegetated, and about 39.4 ft (12 m) from the stream. The cavity in which the nest was placed was 9 in (22.8 cm) deep, 13.6 in (34.5 cm) wide by 9 in (22.8 cm) high at the entrance, and sloped slightly downward.

The second active nest was also found at an elevation of 5,200 ft (1,585 m) along a stream in the Alakai Swamp; its locations was similar to that of the first nest. Large hard weevils (Rhyncogonus spp.) are an important prey species for this bird, as are spiders and caterpillars. The insectivorous habits of the small Kauai thrush—an adult was seen carrying a very large, green looper caterpillar—are strongly contrasted with the berry-eating propensities of the other members of the genus.

Habitat

The small Kauai thrush has always been restricted to dense ohia forests in the Alakai Swamp. The favorite historical spots for this bird were places where koa grew amongst the brushwood and the ground was covered with dead leaves and fallen twigs. This ideal habitat may today only rarely exist now that much of the fringe of koa has been altered by the grazing of cattle, the browsing of goats, and the incursions of aggressive exotic plants.

Distribution

The small Kauai thrush, always the rarest of the Hawaiian thrushes, was recognized from the time of its discovery as a species with limited numbers distributed over a highly restricted range. This relative rarity, persisting into recent times, was underscored by field survey results from the period 1968-1973 that gave an estimated total small Kauai thrush population of 177 individuals. Of these, 157 occurred in the north Alakai Swamp, six in the southeastern Alakai Swamp, and 14 in the area west of the Alakai Swamp. Current estimates are essentially unchanged.

Threats

Evaluating the recovery needs of this species has been hampered by difficulties in detecting and studying the species. Surveys done in the early 1970s suggest that the species is at least as numerous and widespread as previously thought, although still very rare and highly endangered. The major factors of decline are the same as for the large Kauai thrush: mosquito borne disease, habitat alteration by hoofed mammals and alien plants, and nest predation by rats.

Conservation and Recovery

Be cause the species is critically endangered, the Recovery Plan recommends bringing the small Kauai thrush into captivity for the purpose of establishing a breeding and release program that will involve storing frozen semen for reproductive manipulation and the maintenance of the gene pool. Any captive-bred birds resulting from this program would be released into suitable habitat. Procedures of the program would be developed though captive propagation of the closely related omao. The advantage of captive breeding over leaving the species in the wild would be to isolate the secured birds from disease and nest predation, two factors believed to be partially responsible for the decline of the species. Captive breeding would buy time to implement a recovery program aimed at improving essential habitat on Kauai.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/