Mitochondrial DNA suggests recent origins in two coastal avian subspecies in northwestern North America

Genetic studies of subspecies endemic to Haida Gwaii (Queen Charlotte Islands), British Columbia and the Alexander Archipelago of southeast Alaska have frequently found genetic corroboration for these phenotypically based taxa. Divergence and speciation are common among island populations of birds, and evidence suggests this region has fostered such divergence during previous glacial maxima. We examined genetic divergence in mitochondrial DNA (mtDNA) of two coastal subspecies endemic to this region: sharp-shinned hawk ( Accipiter striatus perobscurus ) and great blue heron ( Ardea herodias fannini ). Genetic diversity in both species was remarkably low, with both coastal subspecies possessing only the most common haplotype found in continental populations. We found low but significant population divergence between A. s. perobscurus and continental populations of sharp-shinned hawks and no significant population divergence in the herons. The refugial history of the region suggests that these subspecies may have arisen relatively recently compared with other regional endemics for which genetic and phenotypic data both show divergence. Alternatively, species-wide selective sweeps of mtDNA prior to divergence may have rendered this genetic marker less useful for tracking that divergence.