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. 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.