This story originally appeared in the May/June 2016 issue of Bird Watcher’s Digest.
I have recently been thinking more of bird identification issues that are widespread in North America. Of course, people who write identification articles tend to want to look at problems that have not been tackled before or topics on which they can show a novel viewpoint or concept. Anything that may seem overdone will get less attention, and the perception of being old news means that some of these topics get little coverage in birding magazines for years. But, these identification challenges remain commonplace. In the same way that birders seek out the rarity and sometimes ignore the common, writers also ignore the common—the very topics that require the most attention. With this in mind, let’s think again about the yellowlegs and species that can look like them. The yellowlegs are two widespread and common migrant shorebirds throughout much of our continent that can be encountered in any inland pond, at the Great Lakes, or on the coasts.
There are two yellowlegs species in North America; the larger is the greater yellowlegs, and the smaller is the lesser. If you have seen Ben, Cathryn, and John Sill’s fantastic imaginary-bird book, A Field Guide to Little-Known and Seldom-Seen Birds of North America, one of the best gags in there is the intermediate, or lesser-greater yellowlegs. This imaginary bird is more real than we would like to think! The two yellowlegs species are substantially different in size, but, unfortunately, it is common to see a lone yellowlegs or a small group made up of only one species. In this situation, it really does seem like there is an intermediate yellowlegs, because size is the main feature we use to distinguish these two shorebirds. Size is vital, because their plumage is exactly the same. There is more difference in plumage due to age and season within each species than there is between the two species.
With most birds we have a field mark or two we can look for in the plumage, somewhere, that helps to distinguish it. With the yellowlegs, the plumage does not help much. The one exception occurs in spring-summer. In breeding plumage, the greater yellowlegs is boldly barred on the flanks, whereas the lesser is very weakly barred there. Bold, wide, bars on the flanks of a yellowlegs in breeding plumage tell you it is a greater. Sometimes, greater yellowlegs also appear more strongly streaked on the sides of the breast, specifically juveniles in fall. Otherwise, the plumage will identify age and season but not species.
Size Affects Structure
Size is a convoluted feature, partly because it is difficult to assess on a single bird, but also because size affects the shape and overall structure of a creature. The proportions of a large sparrow and a small sparrow are different; similarly, the proportions of the two yellowlegs species are different. This interplay between size and shape means the yellowlegs species can be separated reliably on features of structure.
Compared with the greater yellowlegs, the lesser is slimmer, thinner-necked, and shorter-billed, with a smaller head and finer legs and sometimes a more peaked or angular crown. The greater yellowlegs is longer-billed, larger-headed, thicker-necked and legged, bulkier, and rounder-headed. The bill is the single most important distinguishing feature because it shows the largest difference and because bills affect the look of a bird’s face/head greatly.
Although we do not always consider this, the look of a face has an inordinate importance in determining how one bird species looks different from another to us (See “Identify Yourself: Face 2 Face with Birds” in the September/October 2010 issue of Bird Watcher’s Digest). The greater yellowlegs has a proportionately longer and thicker bill than a lesser. The best way to assess this length is to compare it to the length of the head. Simply, the length of the bill from the base (feathering) to the tip is about the same as the length of the head from bill base to nape. In greater yellowlegs, the bill is longer than the length of the head. Imagine a rubbery Gumby yellowlegs on which the bill can be bent around back. If you bent it all the way back, on a greater yellowlegs the bill tip would stick out behind the head, whereas it would not on a lesser yellowlegs. Another feature of the greater yellowlegs’ bill is that it is thicker, particularly at the base, and it tends to have a grayish color here. The black nostrils can be seen on this gray background of the bill base. Although lesser yellowlegs may show gray at the base, the bill is so thin that it is difficult to see this, and often the bill is just plain black, making it more difficult to see the nostrils. Often the bill of the greater yellowlegs appears to have the slightest up curve, almost like a godwit. I am not sure if this is a reality or an optical illusion, but it can be seen in the field.
Another structural feature to help with identification is head shape. The head tends to be nicely rounded on the crown and nape of the greater yellowlegs, whereas the lesser yellowlegs has a steeper forehead, a flat crown, and a sharp angle of the nape that creates a slight peak at the rear crown. The head of a lesser yellowlegs looks more angular. Add this to the pinlike, thin black bill and smaller head and you have a bird that looks substantially different from a greater—although it does take practice to recognize this.
The thick neck of the greater yellowlegs sometimes shows more of an S-curve at the base, a bulge at the base, rather than the straighter and thinner neck of the lesser. Roger Tory Peterson cited the legs, and particularly the joints of the legs, as good features to look for. Most people now never mention this feature, but in a good view, the thicker and more substantial legs of a greater yellowlegs do make an impression; the thinner yellow legs of the lesser are not as strikingly robust.
Overall, we tend to be much more visual rather than acoustic creatures. But sound is often a key feature to focus on and learn, particularly on difficult identifications. This is true for the yellowlegs. The basic call given by both yellowlegs is teew! When a yellowlegs is excited, it may just give a run-on session of teew notes, while it looks around and bobs in synchrony with the calls: teew! teew! teew! teew! teew! teew! This can go on for many seconds, with the inter-note duration almost as long as the note itself, but it isn’t that useful for identification. You need to listen to the flight call—usually given in flight, although sometimes while on the ground. Typically, the lesser yellowlegs utters the flight call in series of one or two notes: teew-teew, then a pause, and then maybe additional series of one to two notes. The greater yellowlegs, on the other hand, does something similar, but in series of three or sometimes four notes. The greater yellowlegs also has a throatier, more resonant sound and is certainly louder than the lesser.
On land, the related solitary sandpiper is sometimes confused with the yellowlegs. It is even smaller than the lesser yellowlegs, although it has a stockier body and relatively shorter legs. Rather than being overall grayish above like the yellowlegs, the solitary is a darker brownish above. Also, it does not have yellow, but greenish, legs—but beware: In some lighting situations, a solitary’s legs can look somewhat yellowish. The bill of a solitary is short, like that of a lesser, although thicker-looking at the base, but what gives the solitary a very different look is its bold, white eye ring, like spectacles, on the darker face.
Two other species can look very much like a lesser yellowlegs because of their size: the stilt sandpiper and Wilson’s phalarope in fall/winter plumages. The stilt sandpiper has slightly greener legs, but with a yellow tone. They are long legs as in a yellowlegs, so look at the bill and face. Stilt sandpipers have a longer bill with a noticeable down curve at the end, not the dead straight bill of the lesser yellowlegs. Stilt sandpipers also show a bolder and better-defined pale supercilum. The Wilson’s phalarope has yellow legs in the fall, and they often forage in mudflats showing their legs—not always swimming and spinning in circles, as phalaropes are known for doing. Funny enough, yellowlegs sometimes feed while swimming, although they are not spinning tops like phalaropes. The Wilson’s has an even thinner and more needlelike bill than the lesser yellowlegs, a paler body, and a nearly white and largely unmarked face. While a close look will show some streaking on the neck of a yellowlegs, none is ever present on a phalarope. If the upperparts show pale spotting on the edge of the feathers, that is a yellowlegs; neither the stilt sandpiper nor Wilson’s phalarope will show that pattern.
Yellowlegs are overall grayish, with long, yellow legs that poke out beyond the tail in flight. The rump is white and the tail largely white with some darker barring. Solitary sandpipers are darker-looking in flight, the shorter legs are not so noticeable, and the rump is dark. The tail has white sides with wide dark bars, not the largely whitish-looking rear end of the yellowlegs. The stilt sandpiper and Wilson’s phalarope in flight show a white rump, but a gray, not whitish tail; the phalarope has shorter legs, with only the feet sticking out behind the tail.
The yellowlegs breed in the boreal forest, and there, they actually spend a lot of time up in the trees. Their favorite calling perches are in spruce trees, which is quite a sight to see. Lesser yellowlegs breed slightly to the north of the greater, and are absent from the far east of the boreal forest. The two species often breed near each other, sometimes sharing the bogs with least sandpipers and other more southern shorebirds like short-billed dowitchers. They are early migrants in fall, sometimes arriving south of the boreal zone by late June. As with most shorebirds, the juveniles migrate later than the adults. Juveniles can be identified as such by the very fresh plumage and nicely patterned buffy notches on the upperpart feathers, particularly the scapulars and tertials.
On the West Coast south of the Pacific Northwest, the lesser is rather uncommon, so in California, the greater is the default yellowlegs. I would say that in other parts of the continent there really is no default yellowlegs. In much of the Midwest and the East, the lesser is more abundant. Note that wing molt begins earlier in greater yellowlegs, so obvious feather gaps on a yellowlegs in August–September suggest it is a greater. The two yellowlegs like to wade and will visit ponds with a mud or grassy edge and either fresh or brackish water, yet neither likes open ocean beaches. They tend to forage in calm-water spots, such as salt marsh or estuaries in coastal regions. The lesser has a greater tendency to flock, but the flocks are usually small—a dozen or fewer individuals. The greater tends to be more solitary, or singles are spread out in a foraging spot, but not in a group. Often both yellowlegs are found together, which is helpful for separating them.
Perhaps one of the biggest surprises for me in reading the scientific papers recently was finding out that genetic data clarifies that the greater yellowlegs is more closely related to an Old World species, the greenshank, than it is to the lesser yellowlegs. Other recent research has suggested that various species in which there is a larger and a smaller version, like hairy and downy woodpeckers, in fact may be due to a type of mimicry: One is trying to look like the other and gains a competitive advantage for doing so. We, as birders, may be troubled by many of these tricky identifications, but natural selection pushes for these similarities in some complex manner. If there are birding gods, they are laughing at us! But keep in mind that these near twins, like the yellowlegs, can be separated. It takes practice, looking at them as much as you can, as well as listening to them. As you sort these difficult pairs out, your birder brain is growing, and, believe it or not, other entirely different species will become easier to identify, as well. Enjoy this spring shorebirding.
Alvaro Jaramillo is the author of several bird books and has a fun time guiding birding and nature tours. He lives with his family in Half Moon Bay, California.