The adult iiwi is mostly scarlet, with black wings and tail and a long, curved, salmon-colored bill used primarily for drinkingnectar. The contrast of the red and black plumage with surrounding green foliage makes the iiwi one of Hawaii's most easily seen native birds. Younger birds have golden plumage with more spots and ivory bills and were mistaken for a different species by early naturalists. Observations of young birds moulting into adult plumage resolved this confusion. Along with the Hawaiʻi Mamo, iiwi were used in the feather trade. The iiwi's feathers were highly prized by Hawaiian alii for use in decorating ahuula and mahiole, and such uses gave the species its original scientific name: Vestiaria, which comes from the Latin for "clothing", and coccinea meaning "scarlet-colored". The bird is often mentioned in Hawaiian folklore. The Hawaiian song "Sweet Lei Mamo" includes the line "The iiwi bird, too, is a friend".
Song
The iiwiʻs peculiar song consists of a couple of whistles, the sound of balls dropping in water, the rubbing of balloons together, and the squeaking of a rusty hinge.
Diet
The long bill of the iiwi assists it to extract nectar from the flowers of the Hawaiian lobelioids, which have decurved corollas. Starting in 1902 the lobelioid population declined dramatically, and the iiwi shifted to nectar from the blossoms of ōhia lehua trees. Iiwi also eat small arthropods.
Breeding
In the early winter in January to June, the birds pair off and mate as the ōhia plants reach their flowering maximum. The female lays two to three eggs in a small cup shaped nest made from tree fibers, petals, and down feathers. These bluish eggs hatch in fourteen days. The chicks are yellowish-green marked with brownish-orange. The chicks fledge in 24 days and soon attain adult plumage.
Habitat and Distribution
The largest populations of iiwi inhabit Hawaii Island, followed by Maui with the greatest numbers in East Maui, and fewer than 1% of iiwi remain on Kauai. There may be remnant populations on Molokai and Oahu; very few iiwi have been recorded on either island since the 1990s. They are no longer present on Lānai. Overall, ninety percent of the iiwi population is confined to a narrow band of forest on East Maui and the windward slopes of the island of Hawaii, between 4,265 and 6,234 feet in elevation. They are most abundant in mesic to wet forests at higher elevations. These birds are altitudinal migrants; they follow the progress of flowers as they develop at increasing altitudes throughout the year. It has also been noted that birds on Mauna Kea, Hawaii Island, likely make daily trips from lower elevations to feed on nectar. Seeking food at low elevation exposes them to low elevation disease organisms and high mortality. It has been theorized that the iiwi can migrate between islands and it may be why the bird has not gone extinct on smaller islands such as Molokai. Altitudinal migration complicates population assessment.
Threats and Conservation
Iiwi was formerly classified as a near threatened species by the IUCN, but recent research has proven that it is rarer than previously believed. Consequently, it was uplisted to vulnerable status in 2008. The species was listed as threatened by the United States Department of the Interior on 20 October 2017. Iiwi are listed as a threatened species because of small and declining populations in some of its range and its susceptibility to fowlpox and avian malaria. Avian malaria is an introduced disease that is spread by mosquitoes. Iiwi generally survive at higher elevations where temperatures are too cool for mosquitoes. Many disease-susceptible endemic birds, including iiwi and kiwikiu, became rare to absent at lower elevations, even in relatively intact native forest. In a laboratory study, ninety percent of all iiwi exposed to avian malaria died and the other ten percent were weakened but survived. Avian malaria has been identified as the primary driver of declines in abundance and distribution of iiwi observed since 1900. Iiwi habitat has been reduced and fragmented through various types of land development, including clearing native forest for food crops and grazing. Invasive plants also outcompete and displace native plants that iiwi use for foraging and nesting. Invasive animals impact iiwi in a variety of ways, for example feral ungulates may trample native plants and spread nonnative plants and invasive seeds, further degrading habitat. Feral pigs often create by knocking over vegetation and hollowing out areas that fill with rain water. These have the potential to become incubator sites for mosquitolarvae, which in turn spread avian malaria. Organizations throughout the islands have established nature reserves to protect native habitat. Fencing off sections of land to keep out feral ungulates, especially pigs, goats and axis deer enables native plants to recover from overgrazing and ungulate damage and helps restore native bird habitat. In recent years another threat has put native bird habitat at risk. Conservation groups are diligently working to reduce the risk of spreading a disease called Rapid Ohia Death. This disease along with ōhia dieback and ōhia rust could lead to a rapid decline in ōhia forests, an important nectar source for iiwi.
