Remember the mysterious two-part call of the unidentified Empid?  Nacho Areta left a comment this morning on my last post about the sound, pointing out a third example of the mystery sound in the Macaulay Library — this one attributed to Least Flycatcher.  That’s right, the three different recordings of this sound have been identified as three different species — Yellow-bellied, Alder, and Least!

“Whit-beert” call, labeled as Yellow-bellied Flycatcher. Woodhull Lake, New York, 5/30/1998. ML catalog #106901	“Whit-beert” call, labeled as Alder Flycatcher. Upton, Maine, 6/2/1962. ML catalog #7546	“Whit-beert” call, labeled as Least Flycatcher. Brown Tract Lake, New York, 5/28/1999. ML catalog #100852

Nacho asked why the calling bird in all three cases couldn’t be Least Flycatcher.  As I went back to review my notes on that species, I realized he’d solved the mystery.  I’d already picked out several examples of what I had tentatively named the “pweet series” of Least Flycatcher, and ML 100852 was one of them — I had simply failed to recognize the resemblance to the mystery call.  Once I went looking for it in the Least Flycatcher collection, I found more examples:

Least Flycatcher. Brown Tract Ponds, New York, 5/30/1999. ML catalog #100876	Least Flycatcher. Bruce Peninsula, Ontario, 5/21/1993. ML catalog #63954

And that last recording is the true Rosetta Stone, because not only does it feature the mystery call, but also many nice unambiguous renditions of the species’ song: the snappy, repeated “che-BEK” that clinches the ID of Least Flycatcher.

Nacho points out that this vocalization type doesn’t have to be a 2- or 3-noted pattern; it’s frequently a longer series.  That, plus the somewhat variable nature of the initial “whit” call, partially explains why these Least Flycatcher recordings were able to sneak right past me, even as I looked directly at the spectrograms.  The entire affair highlights the tremendous usefulness of collaboration in solving mysteries like these!  Thanks to Nacho Areta and everybody else who helped out with comments.