More properly called the Kaua’i ‘Elepaio (Chamsiempis sandwichensis sclateri or Chasiempis sclateri), for there are distinct ‘Elepaio populations on both Oahu and the Big Island, this is one of two non-honeycreepers among Kauai’s forest avifauna. It’s a monarch flycatcher, part of a large insectivorous Old World family.
Among the most common of the native birds on Kaua’i, the ‘Elepaio is also extremely inquisitive and approaches humans of its own accord—usually trying to lead them away from its nest by scolding loudly. I’ve seen anxious birds, interrupted on their way to feed their nestlings, scold people despite large moths in their mouths for as long as 15 minutes. (Don’t worry; usually the mate will sneak over to the nest while the other bird distracts the observer.)
Adults are grey above and white below, with white tailtips (the only native forest bird with any tail markings) and wing bars and a white vent (which is striking, and vaguely obscene, because they tend to perch with their tail cocked). Younger birds are cinnamon-rufous where the adults are grey, and many birds are somewhere in between.
Unlike the honeycreepers, in which (we think) females do most or all of the nest construction and incubation, ‘Elepaio take turns at both tasks. The nests remind me of stemless wine glasses, and are very tidy and decorated with lichen. They’re also the easiest nests to find, and superabundant—wherever you pause in the woods, there’s an ‘Elepaio pair inspecting you. (And they really do fly up close and get a good look—all the honeycreepers just ignore you.) Also unlike the honeycreepers, which regurgitate food for their young, ‘Elepaio bring whole insects to their nestlings.
The ‘Elepaio’s various calls are among the most distinctive sounds of the Hawaiian rainforest. Their name is allegedly onomatopoeic, but I honestly don’t hear it. They wolf-whistle sometimes and typically make a strange slide-whistle-y sound. (It’s hard to describe. Here’s a decent recording of one of the Big Island subspecies in which you can hear both the slide whistle and some scolding-like calls.)