There are two sub-species of the northern saw-whet owl: the "Aegolius acadicus" "acadicus" found all around North America and the non-migratory "Aegolius acadicus brooksi" endemic to the Haida Gwaii archipelago in British Columbia.  "A.a. brooksi" is identified by a darker, buffier plumage and has been proposed as a separate species, the Haida Gwaii saw-whet owl. Isolated populations on northern saw-whet owls in the Allegheny Plateau and Southern Appalachian Mountains have been found to be morphological different than mid-range owls and as genetically distinct as the sub-species "A.a.brooksi" in British Columbia.