The Greater Yellowlegs is one of our more familiar shorebirds in San Diego County, dashing about frenetically as it feeds and calling attention to itself with its shrill calls. The Lesser Yellowlegs, however, is much less conspicuous, often overshadowed by its larger relative. In winter, especially, it is far less numerous yet still occurs occasionally, making this pair of remarkably similar species a good subject for a winter issue of Wrenderings.
The most obvious difference, of course, between the Greater and Lesser Yellowlegs is size. The Lesser Yellowlegs' average weight of 81 grams is less than half the Greater's 171. Though as in most shorebirds females tend to be larger than males, in the yellowlegs this sexual dimorphism is slight, not enough to affect field identification. But, as all birders know, the size of an isolated bird is often difficult to assess in the field. Fortunately, yellowlegs are often seen near other shorebirds. The Greater is closer in size to a Willet than it is to a Lesser, while the Lesser is barely larger than a Wilson's Phalarope. Shorebirds that fall between the Greater and Lesser in weight are the dowitchers, Red Knot, and Killdeer, though comparing the sizes of differently shaped birds can be tricky.
The best feature for distinguishing the species when no size comparison is possible is the size and shape of the bill. Compare the length of the bill to the length of the bird's head. In the field, the bill of the Greater looks nearly half again as long as the head; my measurements of specimens suggest the factor is actually around 1.3. The bill of the Lesser is almost exactly the same length as the head. The bills of the two species differ in shape as well: the Greater's bill often curves up slightly, whereas the Lesser's never does, sometimes seeming to droop very slightly at the tip. The Greater's bill is proportionately thicker, too; measured from side to side at the base, it is about half again as thick in proportion to length as the Lesser's.
Plumage, however, is of no practical help with identification. Both species have a white belly and the same shape of a white rump patch on an otherwise mottled gray and white body. The legs are the same shade of bright yellow, occasionally intensifying into reddish. From juvenile to adult winter to breeding plumage the species parallel each other closely. Juveniles have the upperparts grayish delicately spotted with whitish or buff and the breast softly streaked with gray. Adults have the upperparts gray, the feathers edged in white or black and white bars. In breeding plumage, seen both before the adults depart in spring and after they arrive in "fall" (actually midsummer), the gray feathers are replaced by blackish ones with sharper white tips, giving the birds a more boldly patterned look. On the underparts especially the streaking becomes much blacker and takes the form of chevrons on the sides.
As so often between birds that look similar, the calls of the Greater and Lesser Yellowlegs differ conspicuously. The Greater's shrill whistle resembles the Willet's scream and is almost always given in a quick series of three, as an alarm as the bird flies off or as it bobs its head nervously. It is a common sound wherever shorebirds feed--nearby Mockingbirds sometimes pick it up and add it to their repertoire. The Lesser is far less vocal, often silent. When it does call, the sound is lower pitched than the Greater's whistle, despite the Lesser's smaller size. It is a soft tooting given hesitantly, usually two or three times, and sounds very similar to the diagnostic call of the Short-billed Dowitcher.
The difference in the quality of the calls is reflected in the birds' behavior. The Greater often dashes impetuously back and forth on the mudflat or shoreline, making the Greater the most noticeable bird in a mixed flock. The Lesser forages more sedately and can easily be overlooked in a mixed flock. When C. W. Michael reported nine supposed Lesser Yellowlegs, a remarkable number for winter, on Mission Bay in January 1935, he wrote of one of the birds, "he did not forage systematically, but moved rapidly along, making flashing jabs in the mud ... constantly jerking his head from side to side. During occasional pauses he would up-bob his head in the manner of a Willet, only more so.... The Yellow-legs jabbed indiscriminately. His system, if any, was to work fast, jab everywhere miss or hit, and by covering more ground than the systematic probers he would fare as well in the end. And besides, all his actions seemed to indicate a nervous disposition that would not permit of slow but sure methods." This account paints such a vivid picture of the typical behavior of the Greater Yellowlegs I have no doubt that it was really the species seen.
It comes as no surprise that most of our records of these shorebirds are along the coast. But both species, especially the Greater, occur regularly inland. Indeed, the Greater Yellowlegs is one of the most frequent shorebirds on inland lakes and ponds. Our atlas effort clarifies what previously was poorly understood, that the Greater Yellowlegs is a regular winter visitor around lakes and ponds not only in the inland valleys but also up to an elevation of 4000 feet. Note the occurrences around lakes Henshaw (square G17), Corte Madera (Q19 and R19), Barrett (S19), and Morena (T21 and T22), as well as around Oak Grove (C16), Santa Ysabel (J18), Wynola (J19), and Long Valley (R21), sites of ponds too small to show on the scale of the map. Now that artificial ponds have been installed in Borrego Springs (G24), Greater Yellowlegs winter there.
Both yellowlegs breed only far to the north of us, in the taiga zone of Alaska and Canada. So the records in our breeding database are of migrants or occasionally, in the case of the Greater Yellowlegs, summering nonbreeders. Though our observation scheme isn't directed toward migrants, we still get quite a bit of information about them along the way. For example, the map shows that the Greater Yellowlegs isn't notably more widespread in migration than it is as a winter visitor. The only really outstanding locality where the Greater Yellowlegs is recorded as a migrant but not as a winter visitor is Lake Cuyamaca (M20), perhaps just a bit too cold for wintering yellowlegs. The Greater Yellowlegs is not a highly gregarious species; generally our records are of fewer than 10 individuals. A notable exception, though, is Laurie Gammie's count of 45 in Bonsall (F8) on 3 April 1998, an exceptional concentration suggesting the peak of the species' spring migration. Unlike some other shorebirds such as the Willet, Marbled Godwit, and Black-bellied Plover, nonbreeding (subadult?) Greater Yellowlegs generally don't stay with us through the summer. But a few evidently do, and unlike those other summering shorebirds these yellowlegs are as likely to be inland as along the coast. Inland, Pete Ginsburg saw one at O'Neill Lake on 28 May 1998, and Ed Hall saw another at the east end of Lake Hodges (K11) on 3 June 1997; coastally, Kathy Estey saw one at Los Peñasquitos Lagoon (N7) on 5 June 1999, and Barbara Moore saw another at Chula Vista (U10) on 30 May 1999. Fall migrants usually arrive in the last few days of June but rarely as early as the third week of June--fall migration seems the most likely explanation for a Greater Yellowlegs I saw at Chollas Reservoir (R11) on 18 June 1998.
The Lesser Yellowlegs is far more restricted and less numerous than the Greater. At the peak of fall migration in August and September it may be fairly common, but over the past two winters we have only 13 records, making it only 5% as frequent as the Greater, and none of these records is of more than two individuals. Southern California lies at the northern extremity of the Lesser Yellowlegs' normal winter range. All but one of the winter records in our atlas database are coastal or just a short distance inland in the San Dieguito River valley (M8). The only exception is Orval Carter's sighting of two in southwest Escondido (J10) on 19 February 1998, and I suspect that these were actually early spring migrants. Interestingly, some of the larger numbers of spring migrants reported have been inland rather than along the coast, notably Margaret and Bert McIntosh's count of three at the Ramona pond (K15) on 19 March 1998 and Robbie Fischer and Andy Lazere's of eight (an exceptionally high number for spring) along the Santa Margarita River in Camp Pendleton (F5) on 12 April 1998. From the Anza-Borrego Desert there is only a single record in our atlas database (21 March 1999 at the Borrego sewage ponds, H25, Paul Jorgensen) and just three earlier ones (all April) in the state park's database.
The Lesser Yellowlegs is not known to stay the summer in San Diego County. The latest date in spring (20 April 1998, Ramona pond, Margaret and Bert McIntosh) and earliest date in fall (4 July 1997, Batiquitos Lagoon, Rita Campbell; 4 July 1999, San Elijo Lagoon, Pete Ginsburg) approximate what was known previously of the species' migration schedule.
So be on the lookout for the occasional Lesser Yellowlegs this winter, but beware of falling into the same trap as did C. W. Michael 65 years ago!
Philip Unitt, from the winter 1999 issue of WRENDERINGS