{"id":2996,"date":"2011-06-13T13:36:52","date_gmt":"2011-06-13T19:36:52","guid":{"rendered":"http:\/\/earbirding.com\/blog\/?p=2996"},"modified":"2016-11-25T08:13:36","modified_gmt":"2016-11-25T14:13:36","slug":"the-western-flycatcher-problem","status":"publish","type":"post","link":"http:\/\/earbirding.com\/blog\/archives\/2996","title":{"rendered":"The “Western” Flycatcher Problem"},"content":{"rendered":"

In 1989, the American Ornithologists’ Union split the Western Flycatcher<\/a> into two species: Pacific-slope Flycatcher (Empidonax difficilis<\/em>) and Cordilleran Flycatcher (Empidonax occidentalis<\/em>), on the basis of vocal differences, differences in allozyme frequencies, and an area of sympatry in the Siskiyou region of northern California, where they were reported to mate assortatively<\/a>.<\/p>\n

Ever since then, these two species have been causing headaches for birders all across western North America.\u00a0 The conventional wisdom is that they are impossible to identify by plumage or structure, even in the hand.\u00a0 Voice is the only field mark.<\/p>\n

Male position note<\/h4>\n

Most birders use only one clue to identify these two species: the subtle but distinct difference in the position notes of the males.\u00a0 Pacific-slope gives a one-syllabled upslurred whistle, and Cordilleran gives a two-syllabled upslurred whistle:<\/p>\n\n\n\n
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