Occurrence and taxonomy of Arctic Warblers (Phylloscopus borealis) sensu lato in North America

We reviewed the taxonomic status of Arctic Warblers (Phylloscopus borealis) sensu lato occurring in North America following the splitting of the complex into three species by the American Ornithologists' Union (Chesser et al. 2014). We used phenotypic and genetic markers to assess the status of this species complex in North America and identified Arctic-type warblers occurring in the Aleutian Islands as Kamchatka Leaf Warblers (P. examinandus). This species occurs at least occasionally through the Bering Sea, to the Alaska mainland, and as far east as arctic Canada. Measurements of Arctic and Kamchatka Leaf warblers were found to differ by only a small degree, offering no simple diagnostic characteristics. In addition, we recommend maintaining the long-recognized Alaska subspecies P. b. kennicotti as a synonym of P. b. borealis.