Birding 101: Juvenile Least and Western Sandpipers

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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.

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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. 

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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. 

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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. 

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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. 

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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. 

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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.  

1

My fav thing to do this time of year is to study the shorebirds as they pass through. The posture description you give is right on. Watch Least, they do tend to pick up food right in front of their feet, Western reach out more. Also I can’t emphasize the importance of studying the shape of every Western you see, the blocky-head, longer neck, and smoother belly. It will help you when you find a more rounded-smaller headed, stout-short-necked, more rounded breast to belly Semipalmated Sandpiper :).

2

Fantastic article.
I spend a lot of time out at Fernhill. I do my best to tell the difference. I’ve only been birding since March and there are many that are confusing. I’m going to make an outline of this article and take it with me to use this week when I go out to Fernhill. I’ll try it out and see how it works. I love when I run into experienced birders out there. I learn so much. So far they’ve all been very nice.

3

Thanks for the informative article. I’ve relied mostly on bill length/shape in separating these two species. (And this can be problematic when only one species is present, where there is no basis for comparison.) Leg color only seems to be reliable when skies are overcast.

I had not even noticed the difference in feeding habits.

4

Excellent article and photos. I understood bill and leg differences but was still confused about markings, shapes and behavior. So very helpful. Thank you David for taking the time to write this tutorial.

5

Thanks for the “fresh eye” look, Dave. A very helpful reminder to step back and try to see birds through the eyes of less experienced birders.

6

Another helpful and well-presented summary, thanks Dave. The only comments I would offer are that in the fourth photo, I cannot see the humped shoulders in the Western nor the difference in the angle of the back that is suggested (perhaps because the two birds are seen at slightly different angles), and also would caution that the shape of the foreparts of individual shorebirds between and within species can vary significantly depending on their fat loading. When the Pectoral Sandpipers move through this fall, watch for particularly rotund or deep-bellied birds, which can be remarkably heavy-bodied. One thing I would like to point out that is not mentioned by Dave—certainly no shortcoming, as it simply wasn’t in the scope of his excellent discussion—is that inexperienced birders may be confused in seeing a shorebird in a crowded flock of preening peeps that otherwise looks just like a Western Sandpiper but appears about 15% larger. Check to see if this individual is spending a lot of time preening. When Western Sandpipers (in particular, for some reason, but other species as well) preen their upper back feathers, they extend their neck to do so, and they can seem larger or longer than others of the same species that aren’t doing that at the moment. It can be quite confusing. As soon as the bird quits preening and retracts its neck, the illusion vanishes. Birds’ movements are dynamic and fluid and their postures are endlessly plastic, such that the figures in field guides and other portraiture serve only to suggest an “average” appearance, and any given photo may be misleading.

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Dave, thanks for this. I’m on the coast of Maine for two more weeks and I was just out today struggling because every year I have to relearn this stuff. Having spent most of my life living inland and not being particularly interested in shorebirds, it has been a sturggle for this old birder. I’m getting better but it’s info like this that really helps.

8

Thank-you Dave. I think this is the best comparison between the two that I have seen. I have trouble with all the small peeps and will use this the next time I am observing them. Question: do all Westerns have webbing between toes? Do you have any comparisons that include Semi-palmated and Baird’s?

Sue

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Sue, Indeed Western Sandpipers have webbing between the toes, but it is often very difficult to see, so it’s not always a useful field mark. The two links below offer some of the comparisons that you ask about. As you go through the individual photos in each gallery, roll your cursor of the larger selected image in the box to the right of the thumbnails. When you do this the caption for that image will appear. There are number of comparative shots that include various ages of Western Sandpipers (adult and juvs. together) and a couple shots that include juvenile Baird’s, Western, and Least sandpipers all together.

http://www.birdfellow.com/photos/gallery/241-labor-day-weekend-shorebirds-2-5-september-2011

http://www.birdfellow.com/photos/gallery/592-shorebirds

10

As David Fix suggests, there is great plasticity in the posture and shape of feeding shorebirds and no bird should be identified to species on the basis of posture or shape alone. Feather colors and overall color pattern are probably the most reliable field usable characteristics, particularly when you are talking about known age birds in fresh plumage (i.e. fall juvenile shorebirds). Soft part (bill and legs) colors are generally reliable as well, but sexual dimorphism results in highly variable bill lengths in shorebirds of the same species. To correctly ID any bird, there should be a combination of characteristics that match up. These should include plumage color and pattern, bill shape and color, leg color, and size and general shape.

11

Wonderful article! I just started a month ago trying to identify the differences between the Least and the Western at Royal Avenue, Fern Ridge Lake. I’ve found it to be daunting. These tips are just what I need. Thanks Dave.

12

What a wonderful article. Thank you very much for taking the time to wrting it.
Len

13

Excellent treatment of peep jizz, Dave. Such advice may help us find Semipalmated Sandpipers in these migrant flocks. One helpful clue: Leasts tend to favor darker, muddier substrate whereas Westerns favor sandier habitat patches. This preference may be more helpful in wintering flocks than in migrants who tend to forage more opportunistically.

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David Fix is absolutely right that Westerns can appear much larger depending on their posture. At dusk last evening Dave Irons and I saw a Western that was facing us which appeared so large when compared to the nearby peeps that we wondered what it was until it flew off with a group of Leasts and Westerns. It then became the same size as its compatriots.

15

Wonderful article Dave! I just read Max Rae’s post on OBOL and viewed his photos. Then I read this article and went back to Max’s photos. It was like I was seeing the birds with new eyes. :-)

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