Lesser Koa Finch

The only specimens of the lesser koa finch ever caught were a family group with members of different ages and sex, ideal for study. The males were apparently golden-yellow with olive green on the breast and belly. The females were almost indistinguishable from the species' larger relative, the greater koa finch (Rhodacanthis palmeri), other than the fact that the former were slightly darker in color. The juveniles were somewhat mottled on the belly, similar to the females.

The lesser koa finch was endemic to the island of Hawaiʻi. This species was recorded in upland koa (Acacia koa) forests, but likely inhabited lowland habitat until before or shortly after the time of western contact in 1778. The IUCN Red List says, "This or a similar species is also known from the fossil record of O'ahu and Maui," citing a 1991 paper. This apparently refers to the primitive koa finch (Rhodacanthis litotes), a similarly sized species known from fossils on Oʻahu and Maui, described as a new species in 2005.

Its life cycle and feeding habits apparently centered around the koa plant from which it got nectar and fruit (and for which it was named). The koa also provided refuge for small flocks of the finch as it avoided people and the noon high sun. It was seen congregating with its larger relative, the greater koa finch (Rhodacanthis palmeri). Several specimens were collected and sent to London, Cambridge, New York, Philadelphia, and Berlin.