An Under-appreciated ID Challenge

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From this angle, this western Willow Flycatcher, photographed in Lane County, Oregon, might be mistaken for a wood-pewee. It looks brownish above, fairly dark in the face, pale-throated, has dull wingbars, and might even be construed to look "vested."

Some might scoff at the notion that separating the western subspecies of Willow Flycatcher from Western Wood-Pewee can be challenging, but each year I see links to photos of one of these species that is misidentified as the other. The North American wood-pewees and Willow Flycatcher are similar in size, general shape, and coloration. Additionally, neither species typically shows an eyering and their wingbars are buffier and less crisp than those of other Empidonax flycatchers.

As a rule, most birders think of Empidonax flycatchers as being greenish above, pale olive-gray or yellowish below, as having complete eyerings and showing rather crisp and conspicuous wingbars.

We think of wood-pewees as being more dusky-brown above, with dingy grayish to dusky-olive underparts and dull sulphur-yellow that is limited to a narrow trough on the lower belly and undertail. Wood-pewees, particularly Westerns, look somewhat vested below with dark dusky-olive flanks and a paler central belly. The dark sides to the upper breast frame and accentuate a paler throat.

The general appearance of the "Western" Willow Flycatcher falls somewhere in between these two descriptions. In western North America Willow Flycatchers are browner above than other Empids and they generally show no eyering. While the smaller and grayer Hammond's and Dusky Flycatchers can look vested, most other Empids are not distinctly darker on the sides of the upper breast and upper flanks and their underparts show very little if any noticeable contrast. Western Willow Flycatchers often look a bit darker on the upper flanks and sides of the upper breast. Further, aside from the smaller and yellower below Pacific-slope and Cordilleran Flycatchers, other adult western Empids have fairly crisp and comparatively thinner white or whitish wingbars; fall immatures typically have broader and buffier terminal edges to their wing coverts. Adult Western Willow Flycatchers have broader buffy to grayish-tan wingbars.

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These two images of the same Western Wood-Pewee were taken at Fields, Harney County, Oregon on 26 May 2012. Note the fairly obvious wingbars, the peaked hindcrown, the longish bill, and the "vested" look on the bird in the top image. Also note the brownish overall coloration of the upperparts.

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Here's an example of Western Wood-Pewee (above) looking pretty pale and unvested below and showing an almost entirely pale lower mandible (Photo by Scott Carpenter). Compare it to the Willow Flycatcher below and you can understand how one might confuse these two species.

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Another similarity between Western Wood-Pewee and Willow Flycatcher is head profile. Both species have longer bills and more peaked hindcrowns than the other Empids. All Empids can show a peaked hindcrown, particularly when alarmed, but in general Empids are more round-headed than wood-pewees.

In the absence of hearing one of these birds vocalize or having mastered the subtle differences in shape and color, there is one fail-safe method for separating Western Willow Flycatcher from Western Wood-Pewee and that is overall wing length and primary projection.

The Contopus flycatchers (pewees, wood-pewees, and Olive-sided Flycatcher) have much longer wings than Empidonax flycatchers. Further, they have very long primary projection–the distance that the folded outer flight feathers (primaries) extend beyond the folded inner flight feathers (secondaries and tertials).

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In the image of a Western Wood-Pewee (above) I have color-coded the various feather sets in the flight feathers: green are the tertials, red are the secondaries, and yellow are the primaries. the distance along the open end of the blue triangle is often described as primary projection or primary extension. Note how far the primaries project beyond the tips of the secondaries and how the wingtips extend well beyond the upper tail coverts and about halfway down the tail. The flight feather sets of the Willow Flycatcher (below) are similarly color-coded and the primary projection is expressed in the distance across the open side of the blue triangle. If you look closely, you can see that the primary tips are more rounded on the Willow and the overall primary projection is shorter. Also, note the relationship between the wingtips and the tail. The tips of the primaries extend only to the tip of the upper tail coverts and do not extend down the tail (partly obscured by the vegetation).

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This is another dorsal view of a Willow Flycatcher. It's not as easy to see the sets of flight feathers, but this image offers a better view of how the primary tips extend to, but not beyond, the upper tail coverts and the primary tips do not extend well down the tail like they do on a Western Wood-Pewee. Note the warmer olive-brown upperparts of this hatch-year bird and how it does appear to have a very thin pale eyering. 

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Here's another dorsal view of a Western Wood-Pewee. Again, note the exceptionally long primary projection and how far beyond the upper tail coverts and how down the tail the wingtips extend.

In general, Western Wood-Pewees are darker and browner above than Willow Flycatchers. Willows usually look somewhat warmer in overall tone and have some greenish cast to the upperparts, but that is highly dependent on lighting. Western Wood-Pewees are also more strongly vested below, but again this varies considerably depending on lighting conditions. Willows are paler below and usually look less vested and the pale yellow below is more extensive, usually covering most of the lower belly. As a rule, the lower mandible of a Willow Flycatcher is brighter yellow or yellow-orange and often shows no dark on the tip of the underside of the bill. The lower mandible of Western Wood-Pewee is usually a darker fleshy-orange with some dark near the tip. Willow Flycatchers may appear to have a weak eyering, something not seen on a Western Wood-Pewee. 

Given the subjective nature of the plumage differences between Willow Flycatchers and Western Wood-Pewees, I would encourage you to first key in on the obvious structural difference in the wings of these two species. Once you gain a handle on that, their more subtle differences in color and behavior will likely become more noticeable.

1

Very nice discussion/presentation, Dave. I believe that tips on any Empidonax Flycatchers are well worth a read.

2

Thanks for the informative article. Absent vocalizations or size perspective, I’ve always identified Willow Flycatchers by the combo of light(er) hue, the lack of an eye ring, and the extensive light coloring on the lower mandible. However, the mandible coloring of Western Wood-pewees seems to vary to a small extent, and is difficult to tell in other instances (distance, bad lighting, angle, etc.). Knowing the relative differences in primary projection and shape helps.

3

One other little difference I often can see is the the Willow will have a small lighter patch at the lores, the Pewee will have all dark lores, this can be seen in all your photos.

4

Bob Archer offers a great tip on the lore color. I can’t recall ever seeing another article discussing this ID issue, perhaps because most “experts” think of it as being a non-issue. Once you gain familiarity with both species, telling them apart is pretty straightforward. However, flycatchers are a challenge for many birders.

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I wouldn’t scoff. I believe that the biggest problem in first learning Empid ID is confusion with pewees!

More tips for identifying Empids: Empid ID in 3 Easy Steps

6

It’s been years since I’ve seen a scissor-tailed Flycatcher. They don’t fnequert Texas and they certainly don’t swing through Virginia. I’ll keep an eye out for one during my next visit to Oklahoma. Thanks for the post, T.R. It’s a beautiful bird and great coin!

7

Excellent article! Another characteristic that seems obvious from the photos that I didn’t see discussed is that the western wood-pewee seems to have a deeply notched tail which the willow flycatcher doesn’t seem to have.

8

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