Warbling Vireo identification: One species or two?

5/20/2016 | 0

Warbling Vireo, perched, holding a spider in its bill.

Warbling Vireo with spider by mayhaga.

Kenn Kaufman’s column “ID Tips,” about bird identification, appears in every issue of BirdWatching. In our June 2016 issue, he describes what to look for to identify Warbling Vireo and explains why the species may soon be split in two:

BirdWatching Contributing Editor Kenn Kaufman.

BirdWatching Contributing Editor Kenn Kaufman.

At one time, Warbling Vireo was lumped with Brown-capped Vireo, a resident (mostly in the mountains) from eastern Mexico south to Bolivia. Now they’re considered distinct, and many experts think that Warbling Vireo comprises two species in North America, separating the eastern subspecies from the two western subspecies.

Interactions between the forms have been studied most closely in Alberta, where their breeding ranges overlap. There, in addition to subtle visual cues to identification, there are average differences in habitat: The eastern birds tend to be found in aspen groves in open parklands or on the edges of forests, while the western birds tend to be in aspen groves within mixed forests of coniferous and deciduous trees.

The songs differ also. The song of the eastern Warbling Vireo is a musical, continuous warble, usually rising to a high note around the middle and finishing on an equally high note. The song of the western Warbling Vireo is usually a shorter warble with a more broken or choppy sound, slightly less musical, and usually not ending on a high note.

In central Colorado in summer, ace birder Ted Floyd, editor of Birding magazine, has recorded birds singing the western song in the mountains and birds singing the eastern song on the plains, only a few miles away. Further studies in Colorado, Montana, Alberta, and elsewhere may give birders a new challenging species pair to identify. — Kenn Kaufman

Kenn Kaufman’s “ID Tips,” about bird identification, appears in every issue of BirdWatching. The column features the photographs of Brian E. Small. The article above is an excerpt of a column that ran in our June 2016 issue.

Read other articles by and about Kenn Kaufman.


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