Taxonomy
By studying the songs and genetics of individuals in an overlap zone between Troglodytes hiemalis and Troglodytes pacificus, Toews and Irwin (2008) found strong evidence of reproductive isolation between the two. It was suggested that the pacificus subspecies be promoted to the species level designation of Troglodytes pacificus with the common name of ‘Pacific Wren’. By applying a molecular clock to the amount of mitochondrial DNA sequence divergence between the two, it was estimated that Troglodytes pacificus and Troglodytes troglodytes last shared a common ancestor approximately 4.3 million years ago, long before the glacial cycles of the Pleistocene, thought to have promoted speciation in many avian systems inhabiting the boreal forest of North America.
Read more about this topic: Winter Wren