The split of Yellow Warbler into two species in 2025 (by eBird) brings a challenging identification issue into the mainstream. It is possible to identify most by plumage color (more details coming soon), but differences in the shape of body, wings, and bill provide more consistent clues for identification.
- Northern undertail coverts longer and fuller, which contributes to an overall more streamlined and torpedo-shaped body
- Northern bill averages smaller and straighter, Mangrove larger and slightly downcurved
- Northern wings slightly longer, narrower, and more pointed, which is visible in longer primary projection, emarginations closer to wingtip, and secondaries shorter than tertials.
Differences in structure are mostly related to the migratory behavior of the two species. Northern Yellow Warbler is highly migratory, with some populations nesting near the Arctic Circle and wintering in South America, and it has evolved long, narrow wings and a more streamlined body shape for efficient long-distance flight. Mangrove Yellow Warbler is resident in its tropical mangrove habitat, with shorter and more rounded wings and less streamlined body, adapted for short flights.
Males of the Mexican group of Mangrove Yellow Warbler (found in southern Texas) are easily identified by their dark rufous head. Identifying others by plumage color is more difficult, and requires assessing subtle plumage differences across a wide range of variation of age, sex, and subspecies. Most can be identified by plumage, but structural differences are more constant and will always be important to confirm an identification.
Across nearly all of North America only Northern Yellow Warbler is expected, and any Yellow Warblers can be identified as Northern simply by range. In the places where Mangrove Yellow Warbler occurs – in mangrove habitat in the Florida Keys and extreme southern Texas – both species can be found and require more active identification. Northern Yellow Warbler is a common migrant and rare winter visitor in those places, and can be found alongside Mangrove Yellow Warbler for most of the year, from July to May.
There are a few records of vagrant Mangrove Yellow Warblers hundreds of miles from their normal range, and the potential for range expansion, so it is worthwhile to keep an open mind to the possibility of out-of-range Mangrove Yellow Warblers.
Differences between these two species are subtle and variable, and require good views and some experience to judge them correctly. Some individuals will be ambiguous even with detailed study, but a combination of plumage and structural details should allow confident identification of most.
Seems difficult to me. I can somewhat tell the bill, but the undertail coverts- even on the drawing seem to me to be opposite of what they should be,?
These subtle variations become easier to see with practice. Experts don’t necessarily have better vision, just a more refined ability to discern small differences. Try looking at the length of the tail projecting beyond the tips of the undertail coverts, and the relative proportions of that in the two drawings.
Dear David, this article is very helpful in tackling this identification challenge. Being from Europe, I have very limited experience with these warblers, but I tried to use your notes to identify the bird reported to Norther Yellow Warbler as belonging to this species in the following eBird list (photographed in Cuba in August 30th): https://ebird.org/checklist/S193386267. Do you agree with this identification?
Hi Mario, I’m still figuring these out, my current take is to agree this looks better for Northern. The wingtip seems long and primary spacing looks good. But the dark back, gray nape and orange crown seem more like Mangrove. I’ll check back on this one as I learn more, and I’m sure this ID challenge will become clearer as everyone works through it in the coming months and years.
Was there any discussion of splitting the Galapagos population from the Mangrove Yellow?
Galapagos populations have been suggested as a separate species, but a recent genetic study found that the islands were colonized by Central American birds fairly recently, estimated 300,000 years ago, and they are not very different genetically. – Chaves, J. A., P. G. Parker, and T. B. Smith (2012). Origin and population history of a recent colonizer, the yellow warbler in Galapagos and Cocos Islands. Journal of Evolutionary Biology 25(3):509–521. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1420-9101.2011.02447.x
David – your effort to make distinctions to facilitate its ID are commendable and appreciated. But for us in the field, who photographs them , this change is a mess. For instance, in Puerto Rico, where both are observed during migration, it is impossible to identify which individual belongs to which species. Our resident species (or subspecies) is not the Mangrove (petechia) with the obvious rufous colored head – ours is similar to the northern, some bright yellow, others duller and others with distinguishable orange stripes on the chest. Similar to what Tom Stephenson describes in his book ‘The Warbler Guide’ on page 470 as the Golden (petechia complex) gundlachi. There are plenty of similar characteristics on both species (Northern and Mangrove). As photographers, what we do to ID them in our pictures? Since we do no catch/trap them or have both specimens to compare and measure its tail and primaries, and then compare tertial and secondary, for us it is impossible to differentiate at plain sight or from our pictures.
For those of us, particularly in Puerto Rico, who are struggling with correctly identifying the two new species of Yellow Warbler which overlap in winter, I hope you will expand your description on how to tell them apart as soon as possible. I agree with Manuel’s comments.