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Photo by Chandler Robbins.
'I'iwis are some of the most spectacular birds found in the Hawaiian Islands, with their long, decurved bills and striking red and black feathers. This species is still relatively common in high-elevation forests on the island of Hawaii, and has smaller populations on four other main islands; but its high susceptibility to avian malaria could make it extremely vulnerable to the future introduction of mosquitoes capable of surviving at high elevations.
'I'iwis are medium-sized Hawaiian honeycreepers with long, downward-curved, peach-colored bills. Adults of both sexes are bright red overall with black wings and tails. Immature birds are dull yellow in color, rather than bright red, and are streaked overall with black.
'I'iwis have one of the most widespread distributions of all native Hawaiian songbirds, occurring on the islands of Hawai'i, Maui, Moloka'i, O'ahu, and Kaua'i.
Because of 'I'iwis' propensity for seasonal movements in search of flowering trees, it is difficult to assess fully population trends for this species. However, it appears that 'I'iwis are experiencing a population decline, except at higher elevation sites.
'I'iwis breed and winter mainly in wet or moderately wet forests with 'ohi'a and koa as the dominant trees. They can also be found in dry forest dominated by mamane, but do not often breed in such forest. Although the species does occur in drier areas on Hawai'i as low as 300 meters, it is most commonly found above 1,250 meters of elevation, where disease-carrying mosquitoes are not present. 'I'iwis spend most of their time foraging on 'ohi'a trees, feeding primarily on 'ohi'a nectar, but also catching butterflies, moths, and other insects. Mamane nectar is another major part of 'I'iwis' diets, and in some areas, the nectar of the introduced banana poka is also an important food source. Accounts of 'I'iwis from the early 1900s described a coevolutionary relationship between the birds, with their long, decurved bills, and the similarly-shaped, tubular corollas of Hawaiian lobelioids. During the past century, though, many of these lobelioids have become endangered or gone extinct, and 'I'iwis now feed mostly on 'ohi'a flowers, which have open, non-tubular corollas.
On the island of Hawai'i, peak breeding season is between February and June, coinciding with peak 'ohi'a nectar availability. Both sexes sing year-round, with increased song activity at the start of the breeding season. Both adults participate in the construction of the nest, which typically contains two eggs. Incubation lasts 14 days, and young birds leave the nest after about 21 days. Young fledglings are good fliers, capable of flying from tree to tree. As a species, 'I'iwis are strong fliers, well-known for long, high flights within a given island in search of flowering 'ohi'a trees. Iiwis also make daily foraging flights up Mauna Kea Volcano to high-elevation mamane forests when these trees are blooming from September to November.
'I'iwis face many of the same threats facing other native Hawaiian forest birds: habitat loss, avian disease, and introduction of alien plant and animal species. Of these threats, avian diseases, combined with the possible introduction of temperate mosquitoes, may pose the greatest risk to 'I'iwi populations. 'I'iwis are extremely susceptible to avian malaria and avian pox, which are both transmitted by mosquitoes. When bitten just once by a malaria-carrying mosquito, nine of ten 'I'iwis tested died within 37 days; when bitten multiple times by infected mosquitoes, all ten Iiwis died of malaria. The incidence of malaria in wild 'I'iwis is greatest during the times of year when birds move to lower-elevation forests where nectar is available, but mosquitoes are also present. Mosquito-transmitted avian diseases seem to have a greater impact on 'I'iwis than on other Hawaiian honeycreepers. Currently, mosquitoes are confined primarily to the lowlands of the Hawaiian Islands, allowing 'I'iwis relief from avian diseases at higher elevations, but if a temperate, cold-tolerant mosquito species is introduced, it could prove disastrous for Iiwis and other native Hawaiian forest birds.
As a non-endangered species, 'I'iwis have benefited from conservation efforts designed to protect more threatened Hawaiian birds and native Hawaiian forest ecosystems as a whole. These efforts have focused on the protection and restoration of native high-elevation forests, resulting in the creation of Hakalau Forest National Wildlife Refuge and other refuges, parks, and reserves. Control programs have been established to eliminate feral pig populations, which, in turn, eliminates favored mosquito breeding sites and allows for the regeneration of native understory vegetation. Current efforts include control of feral grazers, such as sheep, goats, and deer; mammalian predator control, and control of non-native vegetation.
What Can You Do?
U.S. National Wildlife Refuges provide essential habitat for 'I'iwis, and a great number of other species throughout the U.S. and its territories. Unfortunately, the refuge system is often under-funded during the U.S. government's budgeting process. To learn more about how you can help gain much needed funding for U.S. National Wildlife Refuges, visit: http://www.audubon.org/campaign/refuge_report/
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.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists? Union, Washington, D.C.
Pratt, H.D., P. L. Bruner, and D. G Berrett. 1987. The Birds of Hawaii and the Tropical Pacific. Princeton University Press, Princeton.