Bay-breasted & Blackpoll Warblers

Fig. 1: The dynamic duo. Blackpoll (top) and Bay-breasted (bottom)

For North American birders, Blackpoll Warbler (Setophaga striata) and Bay-breasted Warbler (Setophaga castanea) are the quintessential "confusing fall warbler" pair.

A few diagnostic traits immediately separate the species. Even without seeing these field marks, a first impression of color and contrast is telling. Of course, as with any identification, it's best to observe the bird carefully, collecting as many traits as possible before making the call.

Distinctive Traits

Each species has one field mark that, if present, immediately confirms its identity. For Blackpoll, this distinctive trait is yellow feet. For Bay-breasted, chestnut-washed flanks are what to look for.

However, these traits are variable and sometimes difficult to see, so their absence is not necessarily diagnostic. Check out some of the variation:

Fig. 2: Variability in foot and leg color of Blackpoll Warblers

Blackpoll Warblers show a wide range in leg coloration. Some individuals have entirely bright yellow-orange feet and legs; others have dark legs with yellow only on the underside of the feet. Most birds lie somewhere in the middle, with dark legs and yellow feet. Bay-breasted Warblers, on the other hand, have bluish-gray legs. Their soles may appear pale, but never have a strong yellow tinge.

Keep in mind that foot color may be challenging to discern in unfavorable lighting or poses.

Fig. 3: Variability in flank color of Bay-breasted Warblers

When present as in the birds in Fig. 3, the Bay-breasted Warbler's chestnut-washed flanks are distinctive. This mark ranges from a bold patch of dark bay color, to a diffuse warm brown color across the entire flank, to small patches of brownish wash, contrasting with the yellowish head. Beware colorful Blackpolls with a yellow, not brownish, wash on the flanks.

First impressions

Now let's bring our familiarity with these species to the next level. Take a moment to compare the images above. What is similar across the individuals of the same species, but different between different species? Focus on the colors and the strength of the markings on the head, breast, and nape of the neck.

Even without seeing their distinctive features, one can make a reasonably accurate guess as to the identity of eight individuals above. 

Fig. 4: Blackpoll portraits

Blackpoll first impressions: yellow and dirty gray; streaky; contrasty; a "dirty lemon"

• Predominant color: yellow seemingly overlaid with grayish wash; avg. grayer on nape and sides of neck than Bay-breasted
• Head pattern: dark gray cap extending onto nape, prominent eyeline extending past eye. Cap/eyeline often strongly contrasting with yellow supraloral. Cheek may be dark and contrast with pale throat. Overall a darker, grayer, contrasty head.
• Breast pattern: yellow or white throat and breast, often strongly streaked. May show yellow "hood" extending down breast and onto flanks.

Fig. 5: Bay-breasted portraits

Bay-breasted first impressions: lime green; smooth; low-contrast; a "green olive"

• Predominant color: more uniform olive or lime green; avg. greener on nape and sides of neck than Blackpoll
• Head pattern: weaker cap with greener nape. Duller eyeline often not extending as far past eye. Cheek may be light green or gray-washed. Overall a lighter, greener, less patterned head.
• Breast pattern: often paler white or buffy throat and breast. If present, streaks are usually restricted and faint. May show buffy breast extending onto flanks.

Other supporting traits

Inevitably, some individuals will be tough to judge by impression. Some Bay-Breasted are duller and grayish, and in the right light, Blackpolls may appear to have a more lime-green wash. Thus, it's important to carefully examine all of the above traits, as well as the following supporting cues.

Fig. 6: Wingbar contrast differences.
Top: Blackpoll. Bottom: Bay-breasted

Wingbar contrast: Blackpolls have mid-contrasting wingbars due to having thinner wingbars and lighter wings. Bay-breasted Warblers have higher-contrast wingbars due to thicker wingbars and darker black wings.

Lesser coverts: If the bird's "shoulders" on the bend of its wing look patterned in slaty-blue, that's a good clue that you have a Bay-breasted Warbler. Blackpoll Warblers' lesser coverts have less striking blue and green edging.

Undertail coverts and vent color: Blackpolls have whitish undertail coverts and sometimes a yellowish vent area. Bay-breasteds have buffy to whitish undertail coverts and a sometimes buffier vent area

Bill color & morphology: see Powdermill banding station's in-hand comparison. Blackpolls have a yellow-orange base of lower mandible. Bay-breasted Warblers have a pinkish or gray base of lower mandible. Of the two species, Bay-breasted Warblers are endowed with larger and thicker bills.

That's all, folks!

Please let me know in the comments about any amendments and additions that you think should be included in this article.

Keep an eye out for an upcoming quiz on these two species, as well as an article about how to separate them from drab Pine Warblers.

Fig. 7: Who am I?

References & Images

Identification References

Freiday, Don. “The Freiday Bird Blog.” Bay-Breasted V. Blackpoll Warblers, 28 Sept. 2012, freidaybird.blogspot.com/2012/09/fri-d-bay-breasted-v-blackpoll-warblers.html.

Sibley, David. The Sibley Field Guide to Birds of Eastern North America. 1st ed., Knopf, 2003.

Shultz, Tom, and Ryan Brady. “ID Tip: Blackpoll vs. Bay-Breasted Warbler in Fall.” Wisconsin eBird, Cornell Lab of Ornithology, 16 Sept. 2013, ebird.org/content/wi/news/id-tip-blackpoll-vs-bay-breasted-warbler-in-fall/.

Stephenson, Tom, et al. The Warbler Guide. Princeton University Press, 2015.

Ripma, Eric. “Warbler Identification: Blackpoll vs. Bay-Breasted Warblers.” Nutty Birder, 27 Aug. 2012, blog.nuttybirder.com/2012/08/warbler-identification-blackpoll-vs-bay.html.

Ruddy, Jon. “Bay-Breasted vs. Blackpoll Warblers in Fall.” Eastern Ontario Birding, 21 July 2017, eontbird.ca/?p=6457.

Image Sources by Figure
Figure 1
"Blackpoll Warbler (immature)" by Jeremy Meyer / licensed under CC BY 2.0
"Bay-breasted Warbler" by ba.oconnor / licensed under CC BY-NC-ND 2.0

Figure 2 / Figure 4
Clockwise from top left:
"blackpoll 2 talparo" by Feroze Omardeen / licensed under CC BY 2.0
"Blackpoll Warbler" by Kelly Colgan Azar / licensed under CC BY-ND 2.0
"Blackpoll Warbler (Dendroica striata)" by Dave Inman / licensed under CC BY-NC-ND 2.0
"Blackpoll Warbler 5" by budgora / licensed under CC BY-NC-ND 2.0

Figure 3 / Figure 5
Clockwise from top left:
"Bay-breasted Warbler (works)" by Andy Reago & Chrissy McClarren / licensed under CC BY 2.0
"Bay Breasted Warbler" by Jeff Bryant / licensed under CC BY-NC 2.0 
"Bay-breasted Warbler" by Andy Reago & Chrissy McClarren / licensed under CC BY 2.0
"Bay Breasted Warbler" by Jeff Bryant / licensed under CC BY-NC 2.0 

Figure 6
"Blackpoll Warbler" by Kelly Colgan Azar / licensed under CC BY-ND 2.0
"827 - BAY-BREASTED WARBLER (12-31-13) mt view cemetary, deming, luna co, nm (20)" by Alan Schmierer / public domain

Figure 7
"Bay-breasted Warbler" by Andy Reago & Chrissy McClarren / licensed under CC BY 2.0