When it comes to identifying small olive-green birds with wingbars and eye rings, birders are often left befuddled. Separating flycatchers, vireos, and kinglets can certainly be daunting. Distinctive feeding behaviors and upright perching postures usually yield enough clues for the average birder to differentiate Empidonax flycatchers from vireos and kinglets, as the latter two groups tend to be gleaners rather than flycatching for their prey. After that, many birders will encounter serious roadblocks. One of the most problematic species pairs is Hutton's Vireo and Ruby-crowned Kinglet. 

At first glance, the Hutton's Vireo (above) and the Ruby-crowned Kinglet (below) look nearly identical. The first things that I notice when I compare these two photos are the difference in bill color–horn-colored on the Hutton's and all black on the Ruby-crowned–and the relative proportions of these birds. Hutton's Vireos often appear to have a disproportionately large head that seems almost too big for the rest of the bird, while the Ruby-crowned Kinglet looks more balanced in this regard. Hutton's also have a thicker more blunt-tipped bill, whereas the bill of Ruby-crowned is thinner and more pointed. Finally, you might notice that the pale lores are more defined on the Hutton's and create a slightly spectacled look, while the face of Ruby-crowned Kinglet is plainer and devoid of pattern other than the broken eye ring. (Top photo by Dave Irons, bottom photo by Robert Royse)

Field guides will tell you that Hutton's Vireo has a larger, thicker bill than a kinglet and that its feet are bluish-gray. Conversely, Ruby-crowned Kinglets are described as having a smaller bill and more blackish legs with yellow feet. In the grand avifaunal scheme, either of these species might be described as having a small bill, thus bill size difference is more subjective than objective and is highly dependent on the observer's contextual baseline. Simply stated, if you don't have much experience with these birds, or you haven't confidently identified a Hutton's Vireo, you have no basis for comparison. As for foot and leg color, seeing these differences takes a fairly close-up view with good optics. Additionally, both species tend to be pretty active, moving in and out of the foliage and showing a preference for more shaded areas. Getting a good look at the leg and foot color will occur with about every tenth bird you see. So, how do you identify the other nine?

Over the years, I've found a couple things that I look for as I separate these two species. First, I think that bill color is far more useful than bill size. Hutton's Vireos have a paler, horn-colored bill, which is indeed thicker and larger overall than the bill of a Ruby-crowned Kinglet, while the kinglet's bill is all-black.  Although a Hutton's Vireo's bill may look dark in some light conditions, I can't recall seeing one with a truly black bill. 

Another thing that I look for is the contrast in the wing pattern. While both species have two white or off-white wing bars and dusky olive-green wings, I find that the wings of Hutton's Vireos are less glossy looking and show less contrast overall. While their primary, secondary, and tertial edges are paler yellow, yellow-green, and whitish (tertials only), the contrast in this aspect of their plumage is not as obvious as it is on Ruby-crowned Kinglet, which have brighter yellow whitish to yellow margins on the outer webs of the folded flight feathers. The folded wings and greater coverts of Hutton's seem to be fairly similar in color to the mantle and scapulars. Also, the tertials of Hutton's are dusky colored and less black looking than the tertials of a Ruby-crowned Kinglet.

To my eye, wingbars of a Ruby-crowned Kinglet contrast more with the rest of the wing. Until I started really studying photos in preparation for writing this piece, I didn't fully realize why. When I went online and looked at a bunch of Ruby-crowned Kinglet photos, I hadn't realized that the bases of the secondaries (the exposed flight feathers right below the lower wingbar) are black or nearly so. This field mark is mentioned in the National Geographic Guide and illustrated quite well in the Sibley Guides. I also noticed that inner webs of greater coverts, the whitish tips of which create the lower wingbar, are also black, thus darker than the rest of the upperparts. These features, particularly the black base to the secondaries can be seen well in the in-hand spread wing shots of Ruby-crowned Kinglets at this link: http://www.powdermillarc.org/highlights/2009/latefall.aspx (you'll need to scroll down once you reach the page). I also noticed that the tertials (the inner most folded flight feathers) are near black with crisp white margins on Ruby-crowned Kinglets. 

When I compared the features described in the paragraph above to the same aspects of a Hutton's Vireo's plumage, I noted that neither the greater coverts nor the base of the secondaries are as dark on Hutton's. These feathers are more dusky and generally look greenish rather than black. Additionally, the outer webs of the greater coverts (again right above the lower wingbar) lack the bright yellow edges that can be seen on the same feathers of a Ruby-crowned Kinglet. Collectively, these differences combine to make the wing pattern of a Ruby-crowned more crisp and contrasty than the wing of a Hutton's Vireo.

Note how the bases of the secondaries (red arrows) on these Hutton's Vireos above (Photos by Dave Irons) are a similar green color to the rest of the upperparts and how the edges of the secondaries as conspicuously pale edged as those of the Ruby-crowned Kinglets (below). Compare this look to the wing patterns of the Ruby-crowneds (Photos by Robert Royse and Scott Carpenter). Note the blackish base to the secondaries (red arrows), plus the contrast created by the bright whitish and yellow edges to the primaries and secondaries. Note the near black tertials on the first Ruby-crowned and the lack of definition in the pale lores of these birds. 

The one new thing that I noticed as I studied photos of these species is that Hutton's Vireos consistently look more scruffy faced than Ruby-crowned Kinglets. The feathering on the face and throat area of a Ruby-crowned seems to lay more neatly, giving this species a very smooth, mousy look to the head and face. However, on Hutton's the facial and throat feathering, particularly the area in front of and below the eye and down into the malar region, is often quite scruffy or ruffled-up looking. 

There are two final things that I usually see when I compare these species. First, the head of a Hutton's Vireo almost always looks disproportionately large compared to the overall body size, while the head of a Ruby-crowned Kinglet seems to fit the body size better. Also–and this is mentioned in many field guides–Hutton's have a broad pale yellow loral stripe that connects with the front of the eye ring to create a slightly spectacled look. Ruby-crowned Kinglets are also fairly pale in the lores, but they generally don't show a loral stripe connecting from the base of the bill to the front of the eye ring, thus their face is quite plain. 

Like most birds that are superficially similar in appearance, there is no substitute for repeated study. However, if you can commit these basic elements to memory, I think you'll quickly develop a better search image for each species. As these search images become ingrained, you'll begin to more readily see what is different and be less inclined to get hung up on the similarities. You will also start to associate differences in their appearance with the differences in their movements. 

Like other vireos, Hutton's tend to feed in a hop, stop, head swivel sequence. They are more inclined to sit in one spot for several seconds at a time, all the while turning their heads back and forth looking for non-flying prey (mostly grubs and larvae). As a general rule, they don't flick their wings much and rarely go after prey on the wing. That said, Hutton's Vireos tend to flick their wings and flit around more than other vireo species, which are even more deliberate and lethargic in their movements. Compared to Hutton's Vireos, Ruby-crowned Kinglets are perpetual motion. They flick their wings frequently as they move about and often jump or flit into the air after prey (including flying insects). They also hover as they glean prey from the undersides of leaves. 

For most birders, encounters with Ruby-crowned Kinglet far outnumber their encounters Hutton's Vireo, which has a more limited range and is more habitat specific. I can't over-emphasize the importance of studying common birds. You'll be surprised by what you notice when you take a closer look at birds that you already easily recognize. If you don't occasionally take the time to linger on a Ruby-crowned Kinglet and come to know it well, your chances of recognizing a Hutton's Vireo when one is before you will be greatly diminished. Hopefully, these hints will get you started down the path of readily identifying and recognizing these two species. 

This Song Sparrow, photographed at Eugene, Oregon 13 February 2008, is representative of the birds found west of the Cascade Range in Oregon and Washington and in coastal British Columbia. Visiting birders are often confounded by these birds, which are slightly larger and much darker than the Song Sparrows found across most of North America. Note the conspicuous post-ocular stripe and how it flares towards the nape. Most of the auriculars are gray rather than filled in with reddish brown. (Photo by Dave Irons).

Only a handful of species show the range of geographic variation that one can see in Song and Fox Sparrows. You may have a good handle on the forms that occur close to where you live, but if you travel about the continent you may come face to face with individuals that leave you wondering which species you are looking at. This is particularly true in the Pacific Northwest, where the "coastal" forms of Song Sparrow are slightly larger and significantly darker than those found along the East Coast and across the interior of the U.S. and Canada. 

Sooty Fox Sparrows further complicate matters. Not only are they quite different in appearance than the more easterly Red Fox Sparrow, but for much of the year you will find them in the same brush patches with the equally  unfamiliar looking Song Sparrows of the Pacific Northwest. This article offers some key field marks to look for if you find yourself struggling to separate these species away from your home patch. The best part is, you don't have to have them side by side to sort them out.

A good starting point is bill color. Unlike Fox Sparrow, the bill color of Song Sparrow doesn't change much throughout the year. Their bills almost always look uniform in color. Both mandibles are a dark  and dusky grayish horn color. Only recently-fledged juveniles will show paler fleshy yellow tones on the bill. The bill color in Fox Sparrows is far more variable and changes seasonally. During the breeding season, their bills are generally paler, ranging from pale grayish to dull grayish-pink. Outside the breeding season (October-March), Fox Sparrows will a darker bill color, particularly the upper mandible, with varying amounts of corn yellow on the lower mandible and along the cutting edge of the base of the upper mandible. Birds seen from March-May will show a gradual reduction in the amount of yellow on the bill (Irons 2012). These seasonal transitions in bill color seem to hold true across all four Fox Sparrow groups (Red, Slate-colored, Thick-billed, and Sooty).

The next thing to look at is the face pattern. All subspecies of Song Sparrow have a well-defined  brown or reddish-brown post-ocular stripe that is surrounded by gray or buffy-gray and extends from the back of the eye towards the nape, where it generally flares slightly. In the West, there are three groups of Fox Sparrow subspecies. Sooty, Slate-colored, and Thick-billed Fox Sparrows all lack the strong face pattern that we associate with Song Sparrows and Red Fox Sparrows. Although Red Fox Sparrows have a strong gray and russet face pattern, the auricular patch is usually fairly solid reddish-brown, thus there is no clearly defined brown or reddish-brown post-ocular stripe. 

This bird and those in the next two photos are all Song Sparrows. Note how much paler these birds are compared to the Pacific Northwest form above. All three show conspicuous post-ocular stripes, mostly grayish auriculars, and virtually identical bill color. (All three photos by Robert Royse) 

This after hatch-year Red Fox Sparrow was photographed in June in Manitoba. Note the pinkish bill color with no yellow and how the auriculars are filled with mostly russet feathers. (Photo by Robert Royse).

This adult Sooty Fox Sparrow was photographed in Alaska in May. Note the amount of gray in the unpatterned face and the grayish-pink bill with no yellow. (Photo by Robert Royse)

This presumed Slate-colored Fox Sparrow was photographed in California during March. Like most birds in the Slate-colored, Thick-billed, and Sooty subspecies groups, this bird shows essentially no pattern in the face. Note the yellow on the lower mandible. By March the yellow starts to disappear and it will be gone entirely by June. (Photo by Robert Royse) 

This Red Fox Sparrow, photographed at South Padre Island, Cameron County, Texas 13 November 2011, shows a strong face pattern, but again the auriculars are filled in with reddish brown and there is no clearly defined post-ocular stripe. Note the rich corn-yellow base to the bill. This bill pattern is typical of late fall and mid-winter Fox Sparrows of all four subspecies groups. (Photo by Dave Irons) 

This Sooty Fox Sparrow was photographed in the Pacific Northwest during December. Sooty Fox Sparrows are highly variable in color and can look quite reddish in certain light conditions. They may show noticeable gray in the face like this bird, but don't show a contrasting pattern. Again, note the rich corn-yellow on the base of the bill, which is typical in mid-winter Fox Sparrows. (Photo by Glenn Bartley)

With a good view of the bill color and face pattern, you should be able to readily separate Fox and Song Sparrows, regardless of where you are in North America. By focusing on these two aspects, you can side-step the confusion that is introduced by all the geographic variation in color and you won't get waylaid by Song Sparrows that show a darker or more reddish-brown appearance. 

There are a couple of secondary field marks that may help you confirm that you've made the correct identification. First, the lower rumps and tails of Fox Sparrows are almost always noticeably more reddish than other aspects of the bird. In looking at the Fox Sparrows in the images above, even though the overall tone of these birds is quite variable, you might notice that the tails and lower rumps are slightly more reddish on all of these birds. If you look at the tails of the Song Sparrows, they tend to match pretty closely to the general color of the upperparts and don't contrast with the rest of the bird. The Song Sparrows are also somewhat streaked on the rump, while the Fox Sparrows show unstreaked rumps. 

Finally, the dark markings on the underparts of Fox Sparrows tend to be more crisp with lots of isolated triangles/chevrons and if you look closely at the streaking you can see that the streaks are actually rows of chevrons. Song Sparrows tend to have blurrier streaking, with very few isolated chevrons and the streaks don't appear to be made up of rows of chevrons. Below are sets of images of both Fox and Song Sparrows that illustrate this difference.

This Song Sparrow was photographed during March in Ohio. Note how the flanks streaks are solid with no obvious internal chevrons and there are almost no isolated chevrons on the underparts. (Photo by Robert Royse) 

Note the blurry contiguous flank streaks on this Pacific Northwest type Song Sparrow and the lack of obvious chevrons on the underparts. This bird was photographed in February. (Photo by Glenn Bartley)

This Song Sparrow, photographed during March in Ohio, shows a few isolated triangular markings on the lower breast, but they are more blurry, as are the flank streaks, which generally to be contiguous with no obvious chevrons within. (Photo by Robert Royse)

This Red Fox Sparrow was photographed on the breeding grounds in Manitoba during June. Note the lack of yellow on the grayish-pink bill, the solid reddish auriculars, and the crisp isolated chevrons and triangular russet markings below. Also note how the flank streaking is comprised of rows of chevrons. (Photo by Robert Royse) 

This Sooty Fox Sparrow was photographed during September. It is very heavily marked with individual chevrons underneath and doesn't really show much in the way of streaking. (Photo by Glenn Bartley). By early Fall, Fox Sparrows are already showing the yellow on the bill that is absent during the breeding season. 

This Thick-billed Fox Sparrow was photographed during May in California. Note all the isolated chevrons on the underparts and how the streak along the flanks are actually rows of spaced chevrons. (Photo by Robert Royse)

I'll conclude this photo essay with a bird (see photo below) that might cause a bit of a problem. It was photographed in Michigan during April by Allen Chartier. It shows a quite a bit of gray in the auriculars, which are bordered by russet above and below. It also has the suggestion of a post-ocular stripe, although it is thinner behind the eye and connects to the auriculars rather than dead-ending at the nape like it would on a Song Sparrow. Other clues include unstreaked rump and the tail and lower rump, which are considerably more rusty reddish than the rest of the bird. Finally, if you look closely at the bill, it is still showing some yellow on the lower mandible. We can't see much of the underparts, but otherwise the sum of the parts of this bird add up to Fox Sparrow.

Red Fox Sparrow (subspecies "P. i. iliaca") during April in Michigan (Photo by Allen Chartier)

I will continue to look for pairs of potentially confusing common birds as subject matter for this sort of article. If you have certain birds or groups of species that you wrestle with, feel free to let me know via a comment. We welcome your feedback about these articles and suggestions for future ID articles. 

Experienced birders can likely take a glance at this image and immediately recognize that there are two species in this photo. However, for the novice, or even a moderately experienced birder, some important clues are under water.

While birding a local wetland today, I encountered another birder peering at a modest flock of small sandpipers through his spotting scope. Just before offering my usual "have you seen anything interesting?" I noticed that he had an open field guide in his hand. So instead, I asked, "what are you working on? "I'm trying to sort out Least and Western Sandpipers" he replied. Over the next couple of minutes I offered some pointers and hints about shape, bill length, leg color and where these two species tend to feed. He was appreciative and I moved along hopeful that my assistance had been useful.

It's always good to be reminded that ID issues that you may have worked out long ago are hurdles that newer birders may still be navigating. I don't know how many hundreds of thousands of Least and Western Sandpipers that I've looked at over the past four decades, but it's a large enough number that they are as familiar to me as my own family members. I can readily recognize these species at a distance, often without giving the slightest thought to how I'm doing it. As I walked away from this encounter, it occurred to me that my ability to share meaningful ID hints might be hampered by this familiarity, so I spent the next thirty minutes or so taking comparative photos of these two species as they fed together in the shallows. As I did this, I tried to get shots from many angles and with the birds in the same relative feeding positions. Later, while editing the photos on my computer monitor, I attempted to look at them with a fresh eye. I also forced myself to think about the visual triggers that I use to sort them to species and convert those subconscious clues to more conscious clues that I might better explain in the future.

The leg color on juvenile Least Sandpipers is darker and olive-green rather than paler and yellowish as it typically is on adults. When backlit or shaded their legs can look quite dark. This bird was photographed under overcast skies at Heceta Beach, Lane County, Oregon on 5 August 2012.

Field guides will tell you that Least Sandpipers have yellow or greenish-yellow legs and Westerns have black legs, thus you would think this difference would be easy to see. All too often it isn't. Juveniles and often basic-plumaged adults have darker olive-green legs. If the legs are under water, as they often are in feeding birds, it doesn't matter what color they are. If you are out birding in August and September , when the bulk of the southbound migration of Least and Western Sandpipers occurs, you may be doing so under bright sunny skies. When the sun is high (midday), the bird's body will shade the legs making them look dark. Lower sun angles produce backlighting that will also render this field mark unusable. 

Here's a more helpful shot of the same two birds seen above, only this time the light angle is better and the differences in bill length and color pattern become more obvious. And yet, we still can't see the leg color, which for many birders is the most reliable field mark when separating Western Sandpiper (foreground) from Least Sandpiper (background). In addition to being darker and more uniformly reddish-brown above, note the darker cap of the Least and how that serves to accentuate the whitish supercilium. 

In looking at the photo above, I notice several aspects of color and pattern that I use semi-consciously in separating these birds, especially from a distance, or in situations where the tell-tale leg colors are not discernible. First and foremost, at all ages and in all plumages Least Sandpipers are darker and browner overall than Western Sandpipers; winter adult Leasts are darker gray. Additionally, they are darker and more heavily marked on the breast, particularly the juveniles. Hatch-year Western Sandpipers (juveniles) and adults in basic plumage are essentially unmarked and white on the breast. They may have a little bit of streaking on the sides of the upper breast and extremely fresh juveniles may show a wash (no streaking) of cinnamon buff across the upper breast. Juvenile Leasts have variable amounts of streaking across the entire breast and the breast is usually has a dull brownish wash as well.

Secondly, I look at the head and face patterns. Westerns are paler faced overall with limited dark feathering in the auriculars and a paler, gray cap. Leasts have a more solidly dark brown cap and extensive dark feathering in the auriculars, both of which accentuate the white supercilium. From a distance, the supercilium of a Least stands out, while the supercilium of a Western is more blended into its pale face. 

Finally, I notice whether the rusty scapulars–the feathers between the top of the folded wing and the middle of the back–contrast with the back and rest of the folded wing and wing coverts. The scaps on a juvenile Western tend to stand out and contrast noticeably with nape, back, and coverts, which on a juvenile Western tend to look colder and gray as they do in the photo above. Conversely, a juvenile Least has a warmer, browner nape, back and wing coverts that do not contrast with the scapulars. 

Here's a potentially confusing view of a Least Sandpiper (left) and a Western Sandpiper (right). Note the longer bill, blunter bill tip, and cleaner white breast of the Western. It also has a paler gray look to the nape and back. To my eye, the Least in this image looks slightly pot-bellied very straight backed, while the Western is a bit thicker through the chest and has a modest hump across the shoulders. The Least also has a bit darker cap that is dark brown and darker faced overall, whereas the crown of the Western is paler and more gray in tone and it has very limited dark feathering in the auriculars. 

Here's another slightly different angle of the same two birds seen immediately above. Note how the thickest part of the torso on the Least (on left) is on the lower belly by the legs, while the thickest part of the torso of the Western (on right) is through the lower breast, well ahead of the legs. Again, this image shows the differences breast coloration, bill length, and overall darkness above. The Least is much more uniform brown above, while the Western is generally paler and grayer above with noticeable contrast from the rusty scapulars. 

This image is slightly out of focus and cropped less tightly than the others, thus it may be more representative of a typical view one gets of these birds. Although the fine detail is lost, the general pattern, lightness vs. darkness of plumage, and differences in shape become almost easier to see in this sort of view. In this photo the contrast between the mostly brown and darker Least (left) and the paler and grayer Western (right) are more apparent. Again, note how the contrast between the darker cap and pale supercilium are more obvious on the Least. 

Underexposed images mimic low light conditions, which may significantly compromise how we perceive colors or relative darkness or lightness of plumage. In this photo the Western (left) looks nearly as dark as the Least (right). However, the supercilium still stands out and the breast is clearly darker on the Least, while the supercilium is hard to notice on the whiter-breasted Western. Also, note the back profile. The Western is quite hump-backed in this shot, while the Least has a much straighter back profile. 

There are some elements of shape and proportion that provide helpful clues when trying to separate these birds. Westerns are longer billed and their bill tips tend to be thicker and more blunt than the bill tip of a Least. Further, Westerns often look slightly hump-backed and a bit more chesty and broad across the shoulders. Leasts generally show a straighter back profile, are not as chesty and at times seem to be thickest at the belly rather than thickest in the upper torso like a Western. Beware that the torso profile is at best a subjective feature when sorting these two species and the way the feathers are laying can easily alter our perception of body shape. 

Additionally, there are a couple of behavioral clues that may be useful. Westerns are more likely to be out in the water and feeding belly deep, although the photos here show that either species will feed this way. Leasts are more inclined to feed up on mud completely out of the water and away from the water's edge. When feeding in the water, Westerns seem to tip forward more and I think they are more likely to have their tails pointing upward. Leasts tend to have more horizontal feeding posture, particularly in very shallow water or on dry land. They often squat slightly with bent legs, while Westerns tend to stand more straight-legged and tip forward at a steeper angle. 

Hopefully, these tips will be of use to folks who are still learning the small calidrids, particularly along the West Coast of North America, where Least and Western are the predominant "peeps." However, there is no substitute for spending hours watching these birds feed and interact in mixed flocks, as this is the best way to discover the visual or behavioral clues that consistently work for you. In my own case, I tend to see shape, posture, and overall proportions before I notice color or other aspects relating to plumage. Others may find that they first notice differences in plumage or soft part coloration. If you've found useful field marks not mentioned in this article, I invite you to share them as a comment.  

Here's a comparison with an adult male Violet-green Swallow. Note the band of gray across the breast and how the bank broadens out in the middle and extends a bit farther down the breast. 

While birding east of Portland, Oregon on 4 August 2013, Shawneen Finnegan, Rich Hoyer and I found an odd-plumaged pale swallow in a large mixed group of Tree, Violet-green, Barn, Cliff, Northern Rough-winged and Bank swallows. It was mostly white below and the areas of the upperparts that would typically be dark, were instead pale silvery gray. 

I took several photos of the bird and we watched it on and off for nearly 45 minutes. Based on what I could see, I thought it was a hatch-year Bank Swallow. It was smaller than most of the other swallows and by direct comparison it appeared slightly smaller and shorter-winged than a Violet-green Swallow when perched. It spent most of the time perched on the wires with about 200 other swallows, so we got a good feel for its size and proportion. We did see it fly a couple of times. In flight, the shape and proportion seemed to best fit Bank Swallow in my opinion. Rich thought that it might be a Tree Swallow.

I've seen a number of leucistic or at least partially leucistic swallows over the years. They have been either white/or dappled white, or in a couple of cases creamy-tan overall. None displayed this sort of silvery-gray quality. In fact, until recently, I had never seen any species of bird that showed this sort of gray plumage anomaly. Just recently, Cathy Sheeter found and photographed a mostly gray Swainson's Hawk (I believe in Colorado), which had essentially no brown coloration. She shared the images with Jerry Ligouri, who posted them on his blog. http://jerryliguori.blogspot.com/ 

In the harsh afternoon light, the pale gray band across the breast was often lost in the glare off of the otherwise white breast. In both of these images (above and below) you can see a dark area on the side of the upper breast right below the shoulder. In several images, the darker auriculars appear to extend below the imaginary line extending back from the gape and then there is a paler comma mark behind the auriculars. This pattern is suggestive of Bank Swallow. 

Here's the best of two flight shots that I captured. 

I've spent quite a bit of time online trying to find references to similarly plumaged swallows and found none. I also couldn't find any references to plumage anomalies that involved darker feathering being replaced by gray feathers. If anyone is aware of a description/explanation of this plumage aberration, I would like to learn more about it.