The iiwi’s distinctive beak appears to be adapted to exploit the nectar of the similarly-shaped flowers of lobelioid plants (Campanulaceae) (2) (4) (9), although, with a decline in these species, it now feeds more on the nectar of other plants such as ‘ohi’a (Metrosideros polymorpha) and the introduced banana poka (Passiflora mollissima). Individuals often undertake long flights over the forest in search of flowering trees, and the species is believed to be an important plant pollinator (2) (3) (4) (5). When feeding on a lobelioid flower, the iiwi uses a peculiar technique, perching above the flower before quickly swinging upside down, twisting the body, and probing the beak upwards, where it fits well into the long, downcurved flower (2) (9). A tubular tongue with a brushy tip aids in collecting the nectar. The iiwi will also obtain nectar by piercing or tearing a hole in the base of a flower, and supplements the diet with insects and spiders (2) (3) (4) (5). Interestingly, with a decline in lobelioids on Hawaii, the iiwi’s unique beak is thought to be undergoing an evolutionary change, gradually becoming shorter and less curved (6).
The iiwi has an extended breeding season, although peak breeding occurs between February and June, usually coinciding with the peak flowering of ‘ohi’a (2) (3) (4) (7) (10). The breeding pair remains together throughout the breeding season, defending a small territory around the nest, which is built by both sexes, usually in an ‘ohi’a tree, and is constructed from twigs, bark and lichens. Two eggs are normally laid, and are incubated by the female for around 14 days (2) (3) (4) (5). The young, which initially have a short, straight beak, leave the nest at about 21 to 22 days (2) (3) (4). Outside of the breeding season, the iiwis usually disperse from the breeding area, and may form small flocks, sometimes with other species (2) (3).