'I'iwi
Order: Passeriformes
Family/Subfamily: Fringillidae/Drepanidinae
Genus/Species: Vestiaria coccinea
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Photo by Kate Volz, NZP |
Description
: The brilliant scarlet body plumage of the 'I'iwi is perfectly complemented by the black wings and tail. Their long decurved salmon-colored bills are specialized for sipping nectar from tubular flowers. They are small birds, 15 cm long and 16-20 grams in weight. Although the sexes are similar in appearance, males are slightly larger. Immature birds are a paler yellow splotched with brown. Their plain brown bills brighten in color with maturity. 'I'iwis can produce a wide variety of sounds from strange metallic squeaks to clear flute-like calls.Distribution and Habitat
: The 'I'iwi is a member of the Drepanidinae, the Hawaiian Honeycreepers, a group found only in the Hawaiian islands. The 'I'iwi is locally common in high elevation (above 1,500 m) mesic and wet forests on Hawaii, Maui, and Kaua'i. They were once found on all of six largest forested islands in the Hawaiian chain but are disappearing rapidly on the lower elevation islands of Molokai and O'ahu. Extensive surveys on O'ahu from 1994 to 1996 located only eight individuals. They have been extinct on Lanai since 1929.The prime breeding habitat of the 'I'iwi is dominated by the 'ohia-lehua and koa trees with an understory of tree ferns. They forage yet seldom nest in the dryer mamane/naio forests at higher elevations.
Diet
: The long decurved bill of the 'I'iwi is beautifully adapted to sip nectar from the long tubular flowers of the native Hawaiian lobelioids. They will pierce a hole in the base of the flower and extract the nectar with their brushy tipped tubular tongues. They are important pollinators for many species of native plants. 'I'iwis also glean insects and spiders off the foliage. They forage high above the ground in the mid to upper canopy, and will defend a feeding territory in a heavily flowering tree.As the lobelioids have declined through habitat loss and extinction, 'I'iwis have shifted to feeding more on other native flowers such as the 'ohia-lehua, koa, naio, and mamane. They will also feed on the flowers of the introduced banana-poka vine, an aggressive alien weed that is choking out native vegetation throughout the islands. These flowers have shorter corollas than the endangered lobelioids. This dietary shift may be reflected in the slight (0.5 mm) reduction in average bill length seen over the past century.
Reproduction
: 'I'iwis maintain a monogamous pair bond throughout the breeding season. Courtship includes singing, swaying rhythmically on a perch, and wing-fluttering by the displaying male. The female will solicit food from the male in a courtship feeding ritual that helps maintain the pair bond. Breeding is timed to coincide with the maximum flowering of the 'ohia trees.The female, with some assistance from her mate, builds a cup nest of twigs, mosses, and lichens high in the crown of an 'ohia tree. She lays two whitish eggs with chocolate brown speckles and splotches concentrated at the large end of the egg. Incubation lasts for 14 days.
The altricial chicks have bright orange-pink skin covered with white or pale gray down. Both parents feed the young a diet of insects. They grow rapidly and are able to hop out of the nest into the surrounding foliage by 2 weeks of age. They fledge a week later.
Conservation
: A variety of factors have played a role in the rapid range contraction and dwindling populations of the 'I'iwi and other native Hawaiian birds. Habitat destruction began with the arrival of the Polynesians and accelerated with the advent of European colonization. Forest habitat loss ranges from 50% on the big island of Hawaii to over 85% on O'ahu.Perhaps the most devastating blow to the Hawaiian honeycreepers came when Culex mosquitoes were accidently introduced to the islands in the 1820s by a ship cleaning out its water casks in an island stream. These mosquitoes carry avian pox and avian malaria, diseases previously unknown to the island's birds. Native birds have virtually no immunity to these diseases. Studies on 'I'iwis have shown that a single bite from an infected mosquito causes death more than 90% of the time. Culex mosquitoes have virtually extirpated many native birds from the lower elevations, but fortunately they are less tolerant of the cooler temperatures of the high altitude forests.
Numerous introduced species of birds thrive in the relatively predator free environment and provide a reservoir for avian diseases. Introduced livestock such as pigs, goats, and cattle contribute to habitat destruction. They facilitate the spread of the mosquitoes by destroying the tree fern understory, leaving the hollow decaying trunks of the ferns on the forest floor to fill with rainwater and provide breeding habitat for mosquitoes. Introduced feral cats and black rats prey directly on native birds.
Conservation efforts are concentrating on controlling introduced ungulates by direct hunting and fencing projects that exclude them from prime native habitats. Research is underway to identify disease resistant birds that could be used as founders for restored populations.
References
:Fancy, S.G., and C.J. Ralph. 1998. 'I'iwi (Vestiaria coccinea) In The Birds of North America. No. 327 (A. Poole and F. Gill, Eds.) Philadelphia, PA. The Academy of Natural Sciences; Washington, D.C.: The American Ornithologist's Union.
Pratt, H.D., Bruner, P.L, and D.G. Berrett. 1987. A Field Guide to The Birds of Hawaii and the Tropical Pacific. Princeton University Press, Princeton, NJ.
Please note: There are no longer any of these birds at the Zoo.
