The Rapa shearwater was first described in 1959 as a subspecies of the little shearwater.[3] The holotype was later found to be a juvenile and an adult specimen was described in 2017.[4]
A 2015 genetic study using DNA sequences of the mitochondrial cytochrome b gene, found that the Rapa shearwater is sister to a clade containing the Hawaiian shearwater (Puffinus newelli) and the little shearwater (Puffinus assimilis).[5] Morphological data supports this relationship but the Rapa shearwater is much smaller than the other two species.[4]
Not much is known about its decline. It most likely once occurred on Rapa itself, though this population has been extirpated by the polynesian rat, feral goats, and feral cats.
^Bourne, W.R.P. (1959). "A new little shearwater from the Tubaui Islands: Puffinus assimilis myrtae subsp. nov". Emu. 59 (3): 212–214. Bibcode:1959EmuAO..59..212B. doi:10.1071/MU959212.
^Martínez-Gómez, J.E.; Matías-Ferrer, N.; Sehgal, R.N.M.; Escalante, P. (2015). "Phylogenetic placement of the critically endangered Townsend's Shearwater (Puffinus auricularis auricularis): evidence for its conspecific status with Newell's Shearwater (Puffinus a. newelli) and a mismatch between genetic and phenotypic differentiation". Journal of Ornithology. 156 (4): 1025–1034. doi:10.1007/s10336-015-1189-2. S2CID254157285.