Song also differs between these subspecies, with "Red-backed" birds in northern Arizona singing more complex songs on average (slower trills, often 2-3 trills per song, often with 1-2 non-trill notes at start or end) than our "Gray-headed" Juncos in Colorado. In general there is a gradual transition through the mountains of northern Arizona and New Mexico from the fast, simple, usually 1-trill songs of northern juncos (essentially identical in the Oregon, Pink-sided, Gray-headed, White-winged, and Slate-colored races) to the slow, complex songs of Yellow-eyed Juncos. As you continue south through Mexico, the changes continue, with Yellow-eyed Juncos in Oaxaca singing shorter songs with more different note types and fewer repetitions than Yellow-eyed Juncos in Arizona.
This information probably isn't helpful in identifying off-track migrants, but if one were to find a potential "Red-backed" Junco on territory somewhere in Colorado, song would be a key field mark.
Nathan Pieplow
Boulder
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