In wooded areas coast to coast, throughout late spring and summer, some of the most characteristic sounds are the songs of wood-pewees. The sound changes abruptly at mid-continent because two species — Eastern and Western Wood-Pewees — divide the lower 48 states almost exactly in half, along a line extending from the Dakotas south to Texas.
These trim gray flycatchers tend to perch high, often among foliage, so they are heard more often than they are seen. That’s just as well because they are far more distinctive by sound than by sight. Both are relatively plain, a little larger than the tricky Empidonax flycatchers, with wing bars but no eye-rings. No diagnostic visual marks will help you tell them apart.
In fresh plumage, typical adults of the two species have different color tones. Eastern tends to a more greenish gray on the upperparts and whiter on the throat, and its chest band is paler at the center. Western averages more brownish gray overall, more often with a solid gray chest band. The wing bars tend to be a little whiter and more conspicuous on Easterns. On both species, the lower mandible is dull orange at the base and dark at the tip, but the dark is often more extensive on Western. Unfortunately, there is so much individual variation that none of these differences would be reliable if either species showed up out of range.
Adults molt on tropical wintering grounds, so they are in fresh plumage when they arrive in North America in spring. Their feathers gradually become more worn and faded, and by late summer their wing bars can be obscure. At that stage, lacking eye-rings and wing bars, a wood-pewee might superficially resemble Eastern Phoebe, but that species has a longer tail that it frequently wags, shorter wingtips, and a sharp contrast between dark face and white throat.
In late summer, when adult wood-pewees are looking worn and drab, fresh juveniles are on the scene. They have distinct wing bars, often with a buff tone. Because they look different from adults at the same season and sometimes make odd callnotes, birders in either east or west may be tempted to identify them as the “other” species. They reflect the importance of considering a bird’s age and the condition of its plumage when trying to make a tough ID.
The voices of adults are their best field marks. Most distinctive from Western Wood-Pewee is a harsh, buzzy, descending pzzzzeeyeer. Most distinctive from Eastern Wood-Pewee are clear, plaintive whistles: peeey-ya-weeey, with the first note highest and the second one lowest, and a sharply down-slurred peeey-yerrr. However, it would be misleading to summarize their voices as buzzy vs. clear. Most of the Western’s other notes are clear whistles, and some of the Eastern’s calls have a dry or buzzy quality, so only the full notes described here could be considered diagnostic.
What to look and listen for
Size and shape. Slim, medium-sized flycatchers with slight crest. Primaries extend far past tertials, creating long wingtip.
Pattern elements. Only a faint eye-ring, and no strong contrast on body plumage. Wing bars well defined in fresh plumage, obscure in worn plumage.
Differences in color tone. Eastern Wood-Pewee averages greener gray above, whiter below, with whiter wing bars. Western Wood-Pewee averages browner gray, with darker chest band.
Voice. Highly varied in both species. Diagnostic songs are clear, plaintive peeey-ya-weeey from Eastern and a buzzy, descending pzzzzeeyeer from Western Wood-Pewee.
Average differences between Eastern and Western Wood-Pewees may be obvious on typical individuals. The Western tends to be a slightly more brownish gray above, with wing bars that are slightly less distinct and contrasty. The gray wash across its chest tends to be darker and more continuous. The Eastern tends to be a more greenish gray above and whiter on the throat, with more noticeable whitish wing bars. In both species, the base of the lower mandible is dull yellowish, but the dark area at the tip is usually more extensive on the Western. Unfortunately, there is variation in all of these points, so they don’t allow for certain ID of either species outside its normal range.
Most Empidonax flycatchers are easily separated from wood-pewees because they have conspicuous eye-rings. The exception is Willow Flycatcher, on which the eye-ring varies from faint to absent. Willow Flycatcher also tends to show less contrast in the wing bars than other Empidonax, making it even more similar to wood-pewees. The best distinctions involve structure, not markings. Willow Flycatcher is a more compact bird than the wood-pewees. In particular, its wingtips look much shorter because its primaries don’t extend nearly as far beyond the tertials on the wing. Seen from below, the bill is also wider on Willow Flycatcher than on the wood-pewees. One good behavioral clue: all Empidonax flycatchers wag their tails at least occasionally; wood-pewees don’t.
Wing patterns of wood-pewees vary by season, and it’s helpful to understand why. Wood-pewees go through a complete molt once per year, almost entirely on the wintering grounds. When they come north in spring, they are in the freshest plumage that we will see in North America, with wing bars at their most distinct. Comparing birds in equally fresh plumage, the wing bars tend to be whiter and wider on Eastern than on Western Wood-Pewee. In both species, though, the wing bars become faded and worn as spring turns to summer, and by late summer, the wings may look plain. Wood-pewees with distinct wing bars seen in early fall are young birds still wearing their juvenile plumage.
Several species of pewees live in the American tropics, and one of them reaches Arizona and southwestern New Mexico. The Greater Pewee is locally common in summer in open woodlands of pine and oak in the mountains, mainly above the elevations where the Western Wood-Pewee is most common, but they do overlap in some places. The Greater Pewee is, as the name suggests, a larger bird, and it almost always shows a noticeable erect crest, as in this photo. Its overall color is usually a smoother gray than that of the wood-pewee, especially on the underparts. Its best field mark is often the bright orange lower mandible, which is conspicuous at a surprising distance.
A hard-wired song
Birders who have struggled to identify members of the flycatcher family may have noticed that they are different from other groups of birds. This family includes many examples of challenging species — not just wood-pewees but also Empidonax, crested flycatchers of the genus Myiarchus, some kingbirds, and others — that look almost identical but are separated by diagnostic voices. In fact, voice is a significant part of the identity of the whole family. While most perching birds, from ravens to robins, belong to the Oscine group, flycatchers are Suboscines, defined by a different structure to their vocal apparatus. They’re also different in how their songs develop.
Songbirds in general learn their songs. They apparently have a kind of inner template to help them recognize the voices of their own species, but they won’t learn to sing properly unless they actually get to listen to examples of the song. But flycatchers are different. Studies with several species have shown that they can be raised in isolation, without ever hearing an adult of their own kind, and still grow up to sing flawlessly. The song is not learned but innate, hard-wired into their instincts.
This may be part of the reason why different flycatcher species, like the two wood-pewees, can look so similar to each other. Evidently, their recognition of each other is based very strongly on voice, so visible differences aren’t really necessary for maintaining species boundaries.
This article originally ran in the May/June 2021 issue of BirdWatching magazine.