The ʻelepaios are three species of monarch flycatcher in the genus Chasiempis. They are endemic to the Hawaiian Islands, and were formerly considered conspecific. They measure 14 cm long and weigh 12–18 g. One species inhabits the Big Island, another Oʻahu and the third Kauaʻi. Being one of the most adaptable native birds of Hawaiʻi, no subspecies have yet become extinct, though two have become quite rare.
The ʻelepaio is the first native bird to sing in the morning and the last to stop singing at night; apart from whistled and chattering contact and alarm calls, it is probably best known for its song, from which derives the common name: a pleasant and rather loud warble which sounds like e-le-PAI-o or ele-PAI-o. It nests between January and June.
Uniquely among Hawaiian passerines, the distribution of the ʻelepaio is peculiarly discontinuous. According to fossil remains, the birds did not occur on Maui Nui or its successor islands. Their current distribution is absent from the Maui Nui island group. If this assumption is correct, the reasons are unknown at present. However, the strange "flycatcher finches", extinct honeycreepers of the genus Vangulifer, are only known to have inhabited Maui and probably evolved on Maui Nui. There, they probably filled the same ecological niche as the ʻelepaio did on the other islands. Competition from Vangulifer may thus have prevented a successful colonization of Maui Nui by Chasiempis.