{"id":3667,"date":"2012-04-30T21:39:03","date_gmt":"2012-05-01T03:39:03","guid":{"rendered":"http:\/\/earbirding.com\/blog\/?p=3667"},"modified":"2012-05-16T21:59:14","modified_gmt":"2012-05-17T03:59:14","slug":"identifying-eastern-and-western-warbling-vireos","status":"publish","type":"post","link":"http:\/\/earbirding.com\/blog\/archives\/3667","title":{"rendered":"Identifying Eastern and Western Warbling Vireos"},"content":{"rendered":"
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Warbling Vireo, Illinois, 8\/18\/2010 by Ken Schneider (CC 3.0)<\/figcaption><\/figure>\n

Warbling Vireo is among the many widespread North American species with east\/west vocal forms that meet on the Great Plains.\u00a0 Along with other examples of this type of song diversity (Marsh Wren, Blue-gray Gnatcatcher<\/a>), eastern (gilvus<\/em> group) and western (swainsonii<\/em> group) Warbling Vireos may represent two species, and if they are ever split, song would be the best way to identify them.<\/p>\n

Look at a range map of Warbling Vireo and you’ll see that it continues in a pretty much unbroken swathe across North America.\u00a0 The eastern and western song types meet at the Great Plains\/Rocky Mountains interface, and in at least some of those both occur in a fairly close proximity but remain identifiable to type.\u00a0 For example, Warbling Vireos singing on the eastern plains of Colorado not far from the foothills are typically of the eastern type, while those from the foothills west are of the western type.\u00a0 In the Black Hills of South Dakota eastern types occur in the lower elevations, and are replaced by westerns in the higher ones (Birds of South Dakota).\u00a0 What is not very well studied, however, is whether there is a cline in song types anywhere in their range, and how the birds react to each others’ song types in areas in\/near potential overlap.<\/p>\n

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Warbling Vireo range map by Nathan Pieplow<\/figcaption><\/figure>\n

The plumage of the two forms is extremely similar.\u00a0 Western is often cited as having a darker crown and more defined eyeline, giving it less of the “blank-eyed” look associated with Warbling Vireo.\u00a0 It is also a bit whiter on the underparts and darker on the back, and the bill is slightly thicker (Birds of North America<\/a>).\u00a0 However, these differences are very subtle, not well studied, and hard to see in the field.\u00a0 A much more reliable way to separate the types is by their primary song, which has consistent (if not always obvious) difference.\u00a0 I’ll first talk about the eastern song type, which many readers should be familiar with it, and then contrast the western form.<\/p>\n

Eastern:<\/h4>\n

The song of the eastern Warbling Vireos is what gave the bird its name.\u00a0 It is a pleasant caroling song that rolls along, often ending in an emphatic higher note, transcribed at times as “if I could see it I would seize it and squeeze it til it squirts” or some variation thereof.\u00a0 The song phrases are typically around 2.5 to 3.5s long, and are made up of a series rich whistles that are slightly modulated.\u00a0 In the song of eastern Warbling Vireo, most of the initial notes are near the same pitch, with a few higher notes thrown in towards the end of the song.\u00a0 Below are a couple of examples of eastern song:<\/p>\n\n\n\n
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