Walking On Stilts
Bird legs come in all sizes and colours. The predominant colour is likely black, but terns can have red legs, stilts wear pink and Black-crowned Night-Herons have pale whitish tones that continue down from the belly. One of our commonly seen waders has such prominent yellow legs that it gets its name from that feature. There are three shorebird species in the Genus Tringa that spend time in the London area during migration; Greater Yellowlegs, Lesser Yellowlegs and Solitary Sandpiper.
They are listed in order of size and I didn’t even realize that the Solitary Sandpiper was such a close relative of the other two until checking a field guide. The smallest of the group is also the easiest to distinguish from the other two. Greater vs Lesser can be an identification challenge, so its helpful that they are easy to observe in wetlands and their fall migration stretches out over many weeks (July - November). One can find lots of opportunities to practice getting a handle on who is who.
Greater Yellowlegs look like their slender body is sitting on a pair of #2 school pencils, both in colour and diameter. Why so leggy? The obvious answer is to keep their belly feathers from getting too soggy. They feed by striding around pools of variable depth, and with such long legs, they have a greater range of feeding opportunities. They are a bit more active/aggressive than Lesser Yellowlegs and you may notice their capture methods of plowing through the water to catch minnows or “scything” like a harvester, sweeping their bill back and forth. The voice matches their stature (greater, that is) and they will alert you to their overlooked presence by a forceful “tew, tew, tew” call. If flushed, look for the yellow legs in flight as they extend beyond the tail. The tail is mostly bright white with some barring from mid-length to the tip.
Lesser Yellowlegs are a more petite version of the Greater and although their body size is roughly 2/3 that of a Greater Yellowlegs, the distinction isn’t always obvious if they aren’t side by side to compare. If unsure, look at the bill shape and length for identification. Lesser bills are straight and more needle-like than on a Greater. A closer look at photos of the two species, show bill length on Lesser is equal to the width of the head in side profile, whereas on a Greater it is anywhere between 1.5-2 x longer. You can measure it on a computer screen. I also look for a bit of an upturn on the more robust bill to help ID the Greater. Because of the extended length of the bill on Greater, the nares or nostrils are more conspicuous and located further away from the bird’s head feathers. The sound of a Lesser Yellowlegs is “tu, tu” only two syllables and softer.
Both yellowleg species do a curious body bob, where they will be standing and if alerted, suddenly lift up their body (as if for a better look) and then release it down again. Their plumage looks like a mottled spectrum of taupe with darker brown being the predominant shade in breeding plumage, then transitioning to gray as the back feathers moult into non-breeding status. The barring down the sides also fades into pale gray or disappear as summer days get shorter. Juveniles have more fine white spots across the body than adults.
As you observe yellowlegs moving through the shallows, it looks like their knees bend backwards, compared to ours. The joint that looks like it should be a knee, however, is actually a bird’s ankle and the long bone (tarsus) extending downwards is similar to our foot, but with only four toes at the end. The bone above the ankle joint is the tibia. The bird’s thigh is actually secured far back on the spine, held close to the body for better balance, and not usually seen. The “knee” is covered in belly feathers. If you google “bird skeleton”, a visual will improve my explanation.
The smallest of our Tringa migrants is the Solitary Sandpiper, same genus as the yellowlegs but not nearly as tall and leg colour is greenish yellow. It should have been named “olive legs”. The body colour is quite dark, a dark chocolate sprinkled with white dots. There is a sharp contrast with the white sides and belly. Another field mark of note is the noticeable white eye ring, that almost look like goggles. These traits should distinguish it from the Spotted Sandpiper, a similar common shorebird found in local wetlands with a spotted breast and stripe over the eye.
With a bit of practice, and focus on key field marks, it shouldn't be too hard to master the identification of yellowlegs. There is even another long-legged shorebird called a Stilt Sandpiper but it is a rarity here. Many of you may have been up to Strathroy Lagoons to see the family of Black-necked Stilts, raising a family far from its usual home range. Wading bird legs have adapted and evolved to meet their feeding styles with success and as that retro ZZ Top rock song from the 80's sings, "she's got legs, and she knows how to use 'em".
Photos from top: Greater Yellowlegs, Lesser Yellowlegs, Greater feeding on minnows, Solitary Sandpiper and Spotted Sandpiper for comparison with Solitary