Systematics
Audubon's Shearwater belongs to the Puffinus sensu stricto group of mid-sized and small shearwaters, which is related to the genus Calonectris. The taxonomy of this species is extremely confusing. It is occasionally listed as a subspecies of P. assimilis (the Little Shearwater), but they do not appear to be that closely related. Rather, P. lherminieri seems to belong to an ill-resolved clade also including such species as the Little Shearwater, the Manx Shearwater (P. puffinus) or the Black-vented Shearwater (P. opisthomelas).
The little-known Heinroth's Shearwater (P. heinrothi) is sometimes considered a subspecies of either Audubon's or the Little Shearwater. Though it is likely to be another member of that close-knit group, its actual relationships remain uncertain due to lack of specimens.
Audubon's Shearwater itself has around 10 subspecies. Several have at one time or another been suggested to constitute separate species. For example, the Galápagos Islands population has turned out to be a very distinct species, the Galápagos Shearwater (P. subalaris); it is apparently related to the Christmas Shearwater (P. nativitatis) and together with it constitutes an ancient lineage without other close relatives in the genus. Other taxa were initially assigned to the Little Shearwater and later moved to Audubon's. Analysis of mtDNA cytochrome b sequence data – which is of somewhat limited value in procellariiform birds however – indicates that at least 3 major clades can be distinguished:
Read more about this topic: Audubon's Shearwater