The elepaios are a group of three closely related species endemic to the Hawaiian Islands, and the only members of the monarch flycatcher family (Monarchidae) in the United States. Elepaios occur on the islands of Hawaii, Oahu, and Kauai, but are absent from the other islands, even in the fossil record (1, 2). The form on each island was originally described as a separate species, but they were later lumped (3), and this taxonomy was followed by the American Ornithologists' Union for many years (4). In 2010, based on a combination of genetic, morphological, and behavioral evidence (5, 6, 7), the American Ornithologists' Union approved a petition to split the Elepaio into three species once again (8).
The three elepaio species differ in plumage coloration and vocalizations, and in some aspects of their ecology, including habitat use (9, 10). Elepaios on all islands exhibit a 2-year delay in plumage maturation in both sexes, but the subadult plumage differs among islands in degree of similarity to adult plumage (11, 9). Sexual dimorphism in throat color is more pronounced on younger islands (Hawaii) than on older islands (Kauai).
Unusual among native Hawaiian birds, elepaios use a range of habitats and sometimes inhabit disturbed secondary forest dominated by non-native plant species. They are versatile foragers and use a remarkable variety of behaviors to search for and capture prey at all heights and on all substrates in the forest, including the ground, tree trunks, branches, leaves, and in the air.
The Kauai Elepaio is an adaptable species that inhabits forested habitats ranging from dense rainforest to mesic woodland, and is fairly common and widespread at higher elevations (12, 13). Elepaios are affected by introduced mosquito-borne diseases, but have greater immunity than most of the Hawaiian honeycreepers, and in some areas they are found at low elevations (14, 15). The Kauai Elepaio is the only native forest bird species on Kauai that is not declining (12, 13).
All three elepaio species are long-lived, sedentary, and occupy the same small territory throughout the year, and individuals can be found in the same location year after year. Banded Kauai Elepaios have lived to at least 13 years old. Younger birds in subadult plumage are subordinate and seldom breed, acting as floaters until they acquire their own territory.
Bold and inquisitive, elepaios often investigate and even follow hikers, holding their tail cocked up in a curious posture, and can be attracted easily by squeaking. The elepaios are important in the mythology of the Hawaiian people, and are considered the guardian spirit of Hawaiian canoe makers.