Nihoa Finch

Telespyza ultima

Description

The Nihoa finch, Telespyza (=Psittirostra) ultima, is a songbird that closely resembles the Laysan finch, its nearest relative, in many ways. Although slightly smaller in all dimensions, about 5.5-5.65 in (14-14.4 cm) in length, the Nihoa finch has the same distinctive blue-gray conical bill as the Laysan finch; the birds also have very similar plumage. Male Nihoa finches have a bright yellow head, throat, and breast. There is dark streaking on the upper back, blending to gray on the lower back. Females are streaked with brown overall, are darker above, and have a faint wash of greenish-yellow, particularly on the breast.

Nihoa finches are also sociable and fearless birds in the presence of people, approaching observers to within a few feet. This species was restricted historically to Nihoa Island, although recent fossil finds indicate the prehistorical presence of a form similar to both the Laysan and Nihoa finch on the main Hawaiian Islands.

The Nihoa finch has come full circle in its taxonomic status: first described as a separate species and then considered a subspecies of the Laysan finch, it is now again regarded as a full species. It has been classified as Psittirostra ultima.

Behavior

The omnivorous Nihoa finch eats a wide variety of plant seeds, leaves, fruit, flower heads, small invertebrates (especially fruit fly larvae and pupae), and bird eggs (particularly tern eggs). They seem to require fresh water at least once a day.

Nests are built in holes in rocky outcroppings and are constructed of twigs, grass, shredded paper, and large seabird feathers. Thirteen nests were observed in small fist-sized holes in the rimrock along a gulch, and 12 nests were found in rock faces or rock piles. The elevation of nests ranged between 100-850 ft (30.5-259.1 m). Females lay an average clutch of three eggs, sometimes as many as five eggs, between late February and March. Little information is available on incubation and nesting, but one captive bird was observed to incubate eggs for about 15 days. The young are altricial (naked and helpless). In captive pairs, the female incubates the eggs and the male feeds the female; both parents feed the nestlings and fledglings. These finches are apparently monogamous, although the duration of the pairing is unknown. Males defend a territory of 10-13 ft (3-4 m) around the nest.

The song of the Nihoa finch resembles a canary's; both sexes sing, but males appear to be more vocal.

The Nihoa finch appears to require nocturnal roosting sites. Captive finches were reported to roost at night in the branches, grass tussocks, and rocks; wild birds roost in rock crevices or under piles of loose rocks. These rocky sites appear to be essential for long-term finch survival.

Captive Nihoa finches have lived from 1.5-9.3 years of age; one wild individual was captured and banded twice, 12 years apart.

Habitat

Low shrubs cover the sides and much of the floors of the valleys of Nihoa. Bunchgrasses (Eragrostis ) are more common on the ridges. Finches are widespread throughout Nihoa and will sometimes fly halfway across the island in search of food, but they are more often seen near rocky outcroppings. The birds prefer a vegetated, open habitat; they frequently congregate near the island's few freshwater seeps and temporary puddles. There is a correlation between finch density and the presence of the plants Sida fallax and Solanum, both very important sources of food and cover for the birds.

Distribution

The Nihoa finch is endemic to Nihoa. Population estimates before 1960 ranged from 500 to 1,200 birds. Estimates between 1964 and 1975 suggested a population of 3,000-5,000. Attempts to introduce the bird to other islands within the northwestern Hawaiian Islands specifically Tern Island and East Island—have been unsuccessful. The Nihoa finch is now known only on Nihoa Island. The island supported a population of about 2,225 finches in 1986. This number represents a high density and reflects the bird's versatility and perseverance in pursuing numerous food resources. The population may fluctuate from year to year in proportion to the food and water supplies. The highest density recorded was 43 individuals per acre; this represented an aggregate population in 1968 of 6,686 individuals. Since the entire surface area of the island is only 0.25 sq mi (0.65 sq km), the number of individuals the island can support is limited. Vegetation changes due to rainfall variations determine the production of seeds, insects, and other food sources for the finch, which in turn determine the density of birds the habitat can support.

Threats

Island ecosystems are generally fragile and highly susceptible to the introduction of plants, animals, or microbes from the outside. Exotic plants can quickly outcompete island fauna, and introduced predators can drastically alter the balance of wildlife. In addition, bird populations are highly susceptible to imported avian diseases. All of these factors must be closely monitored and immediate steps taken to counter any introductions.

Conservation and Recovery

Because the Nihoa finch population is highly concentrated, a natural disaster such as a severe hurricane or a tidal wave could destroy a large part of it. Previous efforts to introduce the Nihoa finch to other islands have failed, leaving it especially vulnerable to natural disasters. Forty-two Nihoa finches were transplanted to Tern and East islands in French Frigate Shoals in 1967. The birds on East Island were never seen again; the birds on Tern Island had limited successful reproduction and remained in very low numbers for a few years. Both transplanted populations eventually failed.

The U. S. Fish and Wildlife Service Recovery Plan for the species suggests that a captive breeding program may be needed. In 1909 U. S. President Theodore Roosevelt established the Hawaiian Islands Reservation, to which Nihoa Island belongs. In 1940 the area was designated a wildlife refuge and has now been made a research natural area under the jurisdiction of the Department of the Interior. Entry to the island is prohibited except by special permit.

Because of the absence of predators and avian diseases on Nihoa, the bird populations have been shielded and have lost their competitive adaptability. Therefore, protecting these birds from outside threats is the principal goal of conservation measures. Protective steps include: 1) excluding from the island unauthorized boaters and any alien species they might bring with them; 2) preventing an outbreak of avian disease; 3) monitoring the species and their habitat, especially in the event of destructive weather conditions; and 4) establishing a captive flock in event of stochastic extinction. Because the Nihoa finch has no fear of humans, it is especially susceptible to collection, yet another reason to exclude unauthorized people from the island.

Contacts

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/

Pacific Remote Islands Ecological Services Field Office
300 Ala Moana Blvd., Room 3-122
P.O. Box 50088
Honolulu, Hawaii 96850
Telephone: (808) 541-1201
Fax: (808) 541-1216

References

Banks, R. C., and R. C. Laybourne. 1977. "Plumage Sequence and Taxonomy of Laysan and Nihoa Finches." Condor 79: 343-348.

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

Conant, S. 1983. "Ecological Requirements of the Nihoa Millerbird and the Nihoa Finch, Including an Analysis of Management Options for the Miller-bird." U. S. Fish and Wildlife Service, Honolulu. 47 pp.

Sincock, J. L., and E. Kridler. 1977. "The Extinct and Endangered Endemic Birds of the Northwestern Hawaiian Islands." U. S. Fish and Wildlife Service, Honolulu. 111 pp.

U. S. Fish and Wildlife Service. 1984. "Recovery Plan for the Northwestern Hawaiian Islands Passerines." U. S. Fish and Wildlife Service, Portland.

U. S. Fish and Wildlife Service. 1985. "Plan Approved for Three Songbirds of the Northwestern Hawaiian Islands." Endangered Species Technical Bulletin 10 (2): 8-10.