Large Kauai Thrush

Myadestes myadestinus

Description

The large Kauai thrush, Myadestes myadestinus, is only slightly longer than the small Kauai thrush, reaching a length of about 8 in (20.3 cm). This bird, spotted when immature, by adulthood turns a dull brown tinged with olive above, has a brown forehead, and a black bill that is short and broad. The wing quills are deep brown with the underside a mottled light to smoky-gray; the color becomes lighter on the throat and turns almost white on the belly. The toes and tarsus are brown. The species is also known as Phaeornis obscurus myadestinus.

Behavior

The large Kauai thrush feeds primarily on fruit, berries, flower bracts, winged and larval insects, spiders, caterpillars, and the loopers of geometrid moths. Breeding habits are thought to be similar to those of the related omao, which lays a clutch of one or two eggs that hatch in May or June, although some ornithologists speculate that the breeding season may extend from February though October. Nests, located in the cavities of trees 18-24 ft (5.5-7.3 m) off the ground, are constructed of dead or living fronds, twigs, grasses, and mosses. Adults continue to feed the young for some time after they have left the nest.

All Hawaiian thrushes are accomplished singers and practice their calls at dawn or dusk from the tops of dead trees. Groups of thrushes sing as if performing, with one individual taking up a song when another finishes. These birds sing in intervals during the whole day; they repeat this pattern day after day at all times of the year from the same tree, even the same bough. The large Kauai thrush is crepuscular and diurnal, sometimes singing before the first light of dawn and on into darkness. Hawaiian thrushes have a habit of shivering their wings while perched.

Habitat

The large Kauai thrush was an historical occupant of all of the island's forests, but it is now found only in swampland at higher elevations where the largest tracts of wet ohia forests remain. Deforestation of the island was rapid and severe in the early part of the century when land was cleared for agriculture. The area of undisturbed native forest now totals only about 40,000 acres (16,188 hectares).

Distribution

The large Kauai thrush, the most common forest bird on the island of Kauai during the nineteenth century, vanished from the outer forest by 1928. Its decline has continued throughout this century. Of the six species of native Hawaiian thrushes, three are extinct, the Kauai and Molokai species are nearly extinct, and the omao is still common on the island of Hawaii. The large Kauai thrush is now confined to the forest of the Alakai Swamp. The number of large Kauai thrushes was estimated at about 340 in 1973, but by 1986 the population had plummeted to only 24 birds.

Threats

Avian pox and malaria, spread by introduced mosquitoes, have been a major factor in the decline of many native Hawaiian birds. Most remaining birds live at higher elevations where mosquito populations are low. Scientists are now concerned that a temperate-zone subspecies of the night mosquito may become established at the higher elevations and carry diseases to the remaining forest birds. Predation by the introduced black rat is undoubtedly a factor in the decline of the large Kauai thrush. This rat, found on almost every forested mountain on Kauai, is able to climb trees in search of eggs and young birds. Researchers fear that the mongoose, another introduced bird predator, may soon gain a foothold on the island.

Conservation and Recovery

Since the large Kauai thrush and other forest birds could easily go extinct while recovery efforts are studied and implemented, the U.S. Fish and Wildlife Service (FWS) is experimenting with captive propagation of endangered forest birds. The ultimate goal would be to create a captive flock to furnish birds to supplement remaining wild populations. Little is known, however, about the ability of Hawaiian forest birds to live and breed in captivity.

To test the feasibility of captive propagation, the FWS has begun a trial program in cooperation with several U.S. zoos. In late 1988, 15 pairs of the common amakihi, an abundant honeycreeper, were sent to participating zoos to determine if the birds could live and breed in captivity. Such efforts provide essential information on how to manage a captive propagation program for the rarer Hawaiian forest birds.

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/

References

Berger, A. J. 1981. Hawaiian Birdlife. University of Hawaii Press, Honolulu.

Pratt, H. C. 1982. "Relationships and Speciation of the Hawaiian Thrushes." The Living Bird 19: 73-90.