From: James V. Remsen
LABIRD: I’m fairly sure that Yellow-bellied Flycatcher is the most “over-reported” species in LA. Because I’ve seen so many empid descriptions and photos that were called YBFL that were clearly not, I here provide a few tips on YBFL ID in fall. I am not an expert on the species because I really have not seen many of them, but here’s what I know (additions and corrections welcomed). In fact, I have zeroed the eBird filter almost throughout LA to flush out details and documentation, so be prepared to defend/document your IDs henceforth.
1. YBFL voice. In my limited experience with the species here in LA, I am not sure I have heard one ever vocalize (and Steve Cardiff’s experience is similar) — I would rank it up there with Philadelphia Vireo and Scarlet Tanager for the Fall Migrant Least Likely to Call Award. Obviously, that doesn’t mean that they don’t call at all. The reason I mention this is that (a) Acadian Flycatcher, in contrast, is typically noisy in fall as it defends feeding territories, and (b) Acadian calls can be misinterprted as the YBFL “peeoo” call — Acadians in fall give several calls that many observers do not seem to be familiar with, e.g. a “fyoh” call given in aggressive interactions and a “fee?” territorial (?) call. I am often concerned that people not familiar with the range of ACFL calls are interpreting these calls as YBFL.
2. YBFL fresh plumage in fall: the most important character is a faint yellowish wash in throat — no other empid has this wash (although we do have at least 1 ACFL specimen with an anomalous amount of yellow in throat). It is often concentrated in the center of the throat (impinged upon by greener malar area). A much better name for the species would be Yellowish-throated Flycatcher, especially since many or most empids in fall have some yellow in belly; in fact, yellow in belly is probably the least-important character for separating this species. Beware that true throat color can be tricky because of ambient light (reflections off adjacent foliage). Below the throat is a greenish-olive wash across the breast that has irregular, vague vertical flammulations of paler color. And below that is the belly, which is yellowish to varying degrees. The back is greenish (again beware ambient light). The eyering is complete and distinct. The wings typically look very dark, almost blackish, and the wingbars are pale yellowish or buff (juvs.)
3. YBFL is a relatively small empid with a relatively small bill that often has an orangey lower mandible (often more intensely colored than ACFL or ALFL)
This all refers to “classic” fall YBFL - beware individual variation.
Here are some photos to illustrate various points, all taken recently.
Complete eyeing, greenish back, small bill with orangey lower mandible: https://ebird.org/ebird/view/checklist?subID=S31473019
Dainty appearance, yellow wash on throat, greenish olive breast wash with vertical flammulations: https://ebird.org/ebird/view/checklist?subID=S31436376
Greenish dorsum, blackish wings, greenish breast wash (and this one not particularly yellow in belly): https://ebird.org/ebird/view/checklist?subID=S31511817
Yellowish in throat, greenish wash across breast with flammulations, clean eye ring : https://ebird.org/ebird/qc/view/checklist?subID=S31537606
Dainty, clean eyering, blackish wings, orangey lower mandible: https://ebird.org/ebird/view/checklist?subID=S11728711
In general, empid ID remains the tough problem that it always has, and poorly seen birds should just be listed as “empid sp.” Perception of color is affected strongly by ambient light (sunlight, angle, reflections from vegetation) — the same bird can look differently colored in different light. Photos often seem mildly distorted to me.
And while we’re at it …. given how many “pewee" photographs sent to that have been identified as an empidonax …. empids rarely sit in open, or if so only briefly before darting back into vegetation. They typically make short sallies to leaves and branches, rarely to the air itself. In contrast, pewees invariably sit in the open on bare branches and wires, and make sallies, fairly long, into the AIR for flying insects. Not sure why this critical difference is not emphasized in field guides (other than general diminished attention to behavior as an ID character in birds in most recent guides)
Dr. J. V. Remsen