Tui song is unusually varied, combining fluid whistles with coughs, clicks and grating notes. Watching a bird sing, the beak and throat continue to move through passages where a human listener hears nothing. The species produces components at frequencies beyond comfortable human perception, which is why the song sounds broken up in a way the bird's own output is not.
The two white throat tufts that give the bird its old settler name of parson bird sit at the front of a mostly dark plumage that is iridescent green, bronze and purple in good light. Tui are strongly territorial around good nectar sources and will chase off larger birds, which shapes which trees other nectar feeders can use.
As a nectar feeder with a brush-tipped tongue, the tui is a significant pollinator of native New Zealand plants, and it also disperses seeds when feeding on fruit. Regional song dialects are well documented, though how sharply they are bounded remains a subject of ongoing recording work.