I never heard it sing (once mistook the young Rhodacanthis -Greater Koa Finch song for that of Chloridops), but my boy informed me that he had heard it once, and its song was not like that of Rhodocanthis.
Of the four species in the genus Rhodacanthis, the Scissor-billed Koa Finch and the Primitive Koa Finch became extinct before the arrival of the first Europeans to Hawaii in 1778.