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Q:  I want to improve my flycatcher ID skills, but I keep getting tripped up. Why are some flycatchers so hard to identify? Is there a secret? 
 

Kenn: I often tell people that understanding why a species is difficult to identify can be the key to making an ID. Flycatchers are the perfect example of this idea.  

Birds, like other creatures, must be able to recognize their own kind, at least during the breeding season. While some other animals may identify potential mates by smell or other chemical cues, birds generally rely on sight and sound. That’s good for us—for human birders—because we can learn to zero in on these same visible and audible clues to tell species apart. But groups of birds that rely mainly on sound can present extreme ID challenges for us, especially when they’re silent.

No birds illustrate this better than the tyrant flycatchers (family Tyrannidae). Found only in the Americas, this is still one of the world’s largest bird families, with well over 400 species. And although some are distinctive—like the brilliant red male Vermilion Flycatcher or the elegantly adorned Scissor-tailed Flycatcher—most are drab, and there are many groups in which all the species look virtually the same.

Flycatchers are mostly tropical, and only about 33 species occur regularly north of the Mexican border (with at least another 14 straying in from farther south). But even this reduced selection includes several difficult species pairs or groups. Eastern and Western Wood-Pewees are almost identical to each other. The same is true for Tropical and Couch’s Kingbirds. Several of the crested flycatchers in the genus Myiarchus, especially those that overlap in the Southwest, are very similar. And then there are the 10 small Empidonax flycatchers, perpetually problematic for North American birders.

In the past, some of these birds were considered impossible to separate visually. Advances in recent decades have helped birders to see subtle structural points, like bill shapes and wingtip lengths, to tease these problem species apart. But voice remains the most reliable clue for all of them—more so than for any other family of birds in North America.

Consider two Empidonax species, Willow Flycatcher and Alder Flycatcher. These two are so similar that they were regarded as one species, called “Traill’s Flycatcher,” until 1973. Slight differences allow some typical individuals to be separated visually—but even at a banding station, where the birds can be examined in the hand, many still have to be dismissed as “Traill’s.” Their voices, however, are diagnostic. (See illustration left.) Willow Flycatcher sings FITZ-bew, with the accent on the first, snappy syllable of the song. Alder Flycatcher sings zee-BEEoh, with emphasis on the second syllable before a slight slur. The difference in the songs is subtle (which explains why it was overlooked for so long), but it’s easy to hear, with enough practice.

Even their callnotes are distinctive. Willow Flycatcher gives a sharp, thick Whit that seems to have its hardest sound at the end. The comparable note from Alder Flycatcher is a softer, flatter Kep. Written descriptions convey only a poor idea of the differences, but they’re easy to hear in good recordings. Unlike the songs, which are given mainly by males on the breeding grounds, these callnotes may be heard at any time of year, from females or males.

There’s a reason why voice is important for ID of so many lookalikes in this family. Flycatchers are different, vocally, from all our other birds. They’re classified in the order Passeriformes, the perching birds or songbirds, which includes everything from wrens to ravens. But within that order, flycatchers are placed in a distinct group, the suboscines, often considered slightly more primitive. The main difference is in their vocal apparatus—they have much simpler muscles controlling their syrinx, or sound-producing organ. So they may be physically unable to produce truly complex, melodious songs.

They also develop their songs differently. For typical songbirds, there is an element of learning involved. They may have an internal template, but they won’t ever fully develop the song of their species unless they hear it first. Flycatchers are different: their songs are hard-wired in their instinct. In a classic set of studies, Willow Flycatchers and Alder Flycatchers were raised in a lab, never hearing the songs of their own kind. Some were exposed to the voice of the opposite species, with young Alders listening to recordings of Willow songs, for example. Even so, the males all grew up to sing what were described as “remarkably normal” songs of their own species, proving that these were innate and not learned.   

Thus, in many groups of flycatchers, individuals don’t need to be able to recognize their own species by sight alone. Whether they can recognize each other visually is an open question! But the message for birders is that voice is often everything to making a successful ID. And if you‘re looking at a silent flycatcher, the correct and only identification might be “I don’t know.”