I used inter-island song playbacks and information on geology, ecology, and behavior to investigate biogeography and species limits in the `Elepaio (Chasiempis sandwichensis), a monarch flycatcher (Monarchidae) endemic to the Hawaiian Islands. `Elepaio occur on Kaua`i, O`ahu, and Hawai`i, but are absent on the four islands of the Maui Nui group in the center of the Hawaiian Archipelago. It is unlikely that `Elepaio became extinct on Maui Nui or were excluded by the presence of competing species. `Elepaio are absent in the fossil record on all four islands of Maui Nui, but occur in the fossil record on all three islands they currently inhabit. They have adapted to a variety of forested habitats and are more resistant to alien diseases than other bird species that have persisted on Maui Nui. `Elepaio on each island responded most strongly to songs from their own island. Response to foreign songs was asymmetrical. Hawai`i `Elepaio responded to songs from Kaua`i, suggesting that `Elepaio on Kaua`i and Hawai`i share a more recent common ancestry. The sequence of colonization events that led to the current distribution was most likely: (1) Kaua`i to O`ahu and (2) Kaua`i to Hawai`i. Geologic and genetic evidence indicate the `Elepaio lineage arrived in the Hawaiian Islands ∼1.5–1.9 million years ago. `Elepaio probably were blown from Kaua`i to Hawai`i during storms, skipping several of the stepping-stones in the Hawaiian chain. The low level of foreign song recognition indicates song could inhibit interbreeding and might serve as an isolating mechanism.