Putative Blackpoll Warbler (Dendroica striata) with characters suggestive of Bay-breasted Warbler (Dendroica castanea)
Wyandotte County, Kansas - September 5, 2006

Canon EOS 20D / EF 500mm f/4L IS + 1.4x teleconverter
All photos © 2006 David Seibel

The following is an unedited sequence of a single individual that I initially identified as a Blackpoll Warbler in basic (fall) plumage. Aging and sexing is difficult, but the presence of fine black streaks on the sides of the breast may suggest that it is an adult (AHY) bird. These black streaks should be diagnostic, as no plumage of Bay-breasted should have them. If it is indeed an adult Blackpoll, the lack of dark lateral throat streaks would suggest that it is a female. However, according to Dunn and Garrett, 1997 (A Field Guide to Warblers of North America, Houghton Mifflin, Boston, p. 392), the "soles" (i.e., underside of the toes) of a Blackpoll should always be distinctly yellow, and there is no hint of this in these images, even at full resolution. Other markings that seem unusual for Blackpoll include the greenish sides of the neck (normally grayish), relatively indistinct superciliary line, and distinct whitish eyering. At some angles the throat seems quite whitish, which is also more typical of Bay-breasted than Blackpoll, as is the relatively thick (?), distinctly bicolored bill (much more obvious in some photos than in others). Conversely, the white lower belly and undertail coverts (with only a trace of a yellowish wash) are typical of Blackpoll, as are the sharply pale-edged greater secondary coverts. Could this bird possibly be a hybrid, or is the one supposedly constant character for a fall Blackpoll - yellow soles - also subject to variation?

This bird led to a lengthy discussion (but no consensus) on the ID-Frontiers listserv, archived here:

December 2006, week 2
December 2006, week 3 (items 1 and 3)
January 2007, week 1 (my summary)

Thanks to all who offered comments and opinions, both publicly and privately.
 























Detail of tail pattern and undertail coverts: