The Kauai oo was a Hawaiian forest bird found only on Kauai. In 1987, a recording captured its last known male singing a duet-like call, pausing for a female reply that never came. The recording later spread online as a powerful symbol of extinction, shared in documentaries, classrooms and social videos. It remains in use because the sound makes an abstract loss feel immediate, personal and unforgettable, turning a scientific record into a moment listeners can hear and remember.