Simply stated, sorting out many of the female and immature hummingbirds in the American West is a challenge. In addition to being very plastic in terms of shape and profile, feather iridescence and plumage variation associated with age combine to confound even the most experienced observers, particularly when it comes to the genus Selasphorus. This genus includes three North American species: Allen's Hummingbird, Broad-tailed Hummingbird, and Rufous Hummingbird. Separating them in their female and immature plumages has spawned many a lively debate. 

On 11 June 2012 Shawneen Finnegan and I were birding along Cow Creek Rd. e. of Azalea, Douglas County, Oregon. We came across a yard full of blooming Red Hot Pokers (Kniphofia uvaria) that was teeming with Rufous Hummingbirds. It was hard to to count, but there were about 20-25 hummers buzzing about feeding on these flower heads. Almost all were immature or female-type Rufous Hummingbirds, so I found a roadside vantage point that allowed me to photograph several different individuals. Ultimately, I got photos of about ten different birds, all of which seemed to sub-adults. This photo essay shows some of the variation that one might see in immature Rufous Hummingbirds. I captured all of these images at the described site on 11 June 2012. 

The first five photos show variation in back color, most notably how much rufous or rust color there is on the back, rump, and upper tail. 

Fig. 1. This bird was presumed to be a first-summer male based on the extensive rufous on the upper tail coverts and rump, as well as the near solid dark feathering on the throat.

Fig. 2. This presumed female shows an entirely green back, rump and, upper tail. Generally, perched Rufous Hummingbirds show some exposed rufous coloration on the rump and upper tail. I wondered if this might be a first-summer female, as it is conceivable that the rusty edges on the dorsal feathers of a first-summer female may have worn off this far into a plumage cycle. Hatch-year female Rufous Hummingbirds typically show less dense dark feathering on the lower throat. Note the somewhat alert and stretched-out posture of this bird, which tends to make it look bigger and longer-tailed. The length of the tail feathers contribute to a longer looking tail and support the notion that this is an after hatch-year female. Some might look at this bird and call it a female Broad-tailed Hummingbird, but Howell (2002) suggests that female Broad-taileds have a "colder" face pattern lacking the warmer subtle rufous tones shown by this bird.

Fig. 3. This bird shows what I would call intermediate rufous coloration on the rump and lower back, which makes it a challenge to sex. Notice the compact posture (neck not extended) of this bird and how it looks smaller and shorter-tailed in comparison to the bird in Fig.2. The tail feathers on this bird do look relatively short and may not be fully grown.  

Fig. 4. This individual shows a mostly green rump and back with limited rust coloration showing. This back pattern seems to be pretty typical among immatures, particularly females. The tail look fairly short on this bird.

Fig. 5. Given the amount of rufous on the lower back, rump, and upper tail, which is beyond the maximum typically seen on hatch-year birds, I presumed this bird to be an after hatch-year (first summer) male.

The next seven photos show variations in the throat pattern and flank coloration of immature Rufous Hummingbirds. Of particular interest to me is the amount of dark feathering each bird shows on the chin and center of the throat. Birds that were presumed to be immature males seemed to show more extensive and richer rufous wash on the flanks, along with more dense dark feathering on the throat.

Fig. 6. I find the ventral pattern of this bird to be somewhat ambiguous. Flanks are washed out looking, but the amount of dark feathering below seems pretty dense.

Fig. 7. This bird approaches the minimum amount of dark feathering on the throat and the flank coloration is limited and a bit washed out to my eye. I would call this a hatch-year female. Also, note the elongated and rather streamlined profile of this bird. 

Fig. 8 & 9. Two images of the same presumed after hatch-year male from different angles (above and below). Note the amount of rust coloration on the part of the back that is visible (above) and also note the rather solid dark feathering on the throat. This bird had more dark feathering on the throat than any other immature/sub-adult that we saw at this site. Finally, compare the scrunched-up puffed-out shape of this bird with that of the bird in Fig. 7.

Fig. 10. The amount of dark on the throat of this bird falls between the two birds in the three images immediately above (compare to birds in Figs.7-9). Note the fairly uniform pattern created by the dark lines of feathers across the entire throat. The rust on the flanks seems a bit darker than the first of the ventral shots (Fig. 6). I suspect that this bird is an immature male.  

Fig. 11. When hovering to feed, all hummingbirds have a tendency to look larger and more elongated than they do when perched. 

Fig. 12. This individual shows heavy dark feathering on the sides of the throat and lower cheek on the throat, which pales towards the center of the throat and chin.

I recognize that most folks reading this article aren't likely to invest much time and energy into aging and sexing every Rufous Hummingbird that they see (it can be an exercise in futility). Since I live in Oregon, where Rufous is the default Selasphorus across most of the state, appreciating the variability in Rufous Hummingbirds can come in handy. Occasionally, we see out-of-range reports of Allen's (nesting range extends to Oregon's southern coast) and Broad-tailed Hummingbirds (not known to nest in Oregon, but occurs as a rare migrant). Often times, such reports involve female/immature type birds. Here, the first order of business when considering a report of an out-of-range Selasphorus is to determine why it's not a Rufous.

In conclusion, it's important to point out that I've not studied museum skins of Rufous Hummingbirds, nor have I done any hummingbird banding, thus much of the commentary herein is speculative. I would welcome any comments on the specific age and sex of the birds in this collection of images. The main point was to display some of the individual variation one might encounter when observing this species in the field.

Literature Referenced:

Howell, Steve N. G 2002. Hummingbirds of North America: The Photographic Guide. Academic Press: A Harcourt Science and Technology Company, London, UK. 

Williamson, Sheri L. 2001. A Field Guide to the Hummingbirds of North America (Peterson Field Guide Series). Houghton Mifflin Co. New York, NY.

The links below provide additional photos of Rufous Hummingbirds and discussion of Selasphorus hummingbird ID. 

http://www.schmoker.org/BirdPics/RUHU.html

http://home.pacifier.com/~mpatters/bird/humm/HUMMREPORT.html

http://www.hummingbirdsplus.org/allens.html

http://www.museum.lsu.edu/~Remsen/HUMNETf/RufvsAllen.html

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.

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.

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.

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).

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).

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. 

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.