Answer:

We have a chunky, shorter-legged “horizontal” shorebird on the left and a thinner, longer-legged “vertical” shorebird on the right. It’s always difficult to determine the sizes of birds in a photo, but let’s try. The rightmost bird has legs too long for a peep, more like a Yellowlegs or a Dowitcher, so we are looking at birds larger than peeps. Our largest shorebirds (Godwits, Willets, Curlews, Whimbrels) don’t have bright yellow legs like these birds, so we are looking at birds the size of a Greater Yellowlegs (which is still quite large) or smaller.

Let’s start with the left bird. When thinking about a chunky grayish medium-sized shorebird with yellow legs, Dowitchers immediately come to mind. But we see blackish primary tips sticking out way behind the gray tertials, whereas Dowitchers have very long tertials that almost cover the primaries. Also the tail (visible below the blackish primary tips) is uniform pale gray, but Dowitchers have a barred black-and-white tail.

Look more closely at the back pattern of the left bird, especially the scapulars. Each feather is plain gray with a neat white edge, and the neat edging is typical for shorebirds in juvenile plumage. There is also a thin black border on the inside of the white edge of each feather, making the pattern even more scaly-looking than on most juvenile shorebirds. That pattern is unusual and is found on only a few shorebirds, notably a juvenile Red Knot and a juvenile Temminck’s Stint. Temminck’s Stint would be much smaller (peep size), and much rarer — it is unrecorded in California and almost all records from the United States are from Alaska, where it sometimes occurs as a vagrant from Asia. Red Knot also has a plain gray tail, blackish primary tips, yellow legs, and chunky body. Red Knot is rare but regular in LA County, but is seen more often in adjacent counties where there is more coastal wetland habitat, like at Bolsa Chica (Orange County) or Pt. Mugu (Ventura County).

Now for the rightmost bird. If the left bird is a Red Knot, the right bird is too small for a Greater Yellowlegs, but perhaps it’s a Dowitcher or a Lesser Yellowlegs. The pattern of the upperparts isn’t really right for either of those possibilities. Lesser Yellowlegs has a more complicated pattern, with bars and spots on the feather edges. A juvenile Long-billed Dowitcher has a similar pattern on the coverts and tertials, with each feather having a plain gray interior and an outlined edge, but on a juvenile Long-billed Dowitcher that pattern generally continues onto the back, and involves more rufous tones. Also, on this bird the primaries stick out well past the tertials; this is not right for Dowitchers, which have very long tertials that almost cover the primaries.

Another possibility is a juvenile Wilson’s Phalarope that is molting into 1st basic plumage and already has plain gray basic feathers on the back. But Wilson’s Phalarope is much paler on the back, with more contrast between the light gray back and the darker coverts and tertials. Wilson’s Phalarope also has a very pale throat, unlike this bird. And Wilson’s Phalarope is very front-heavy with legs that appear to be placed too far to the rear.

There is one more species to consider when faced with a bird that seems slightly too slim and long-legged for a Dowitcher and a bit too chunky for a Lesser Yellowlegs but can be confused with either. A juvenile Stilt Sandpiper has a covert and tertial pattern very much like the bird on the right. And by late September, many juvenile Stilt Sandpipers in our area are already molting into basic plumage and have plain gray basic back feathers. The streaks on the breast are also good for Stilt Sandpiper. The posture is also important. Stilt Sandpipers are sometimes found in Dowitcher flocks, and because they have shorter bills and longer legs, they lean farther forward than Dowitchers do when feeding, with their rear end angled higher in the air. A Stilt Sandpiper can sometimes be picked out of a Dowitcher flock by the posture, which is consistent with the bird on the right. Stilt Sandpiper is rare but not spectacularly rare in LA County: sometimes there are multiple birds in one year but some years there isn’t a single record.

We want to use as many identifying characteristics as possible when nailing down a bird identification. So when something unusual about a feeding shorebird captures your attention, be patient and eventually the bird will show its bill and you will have more information for confirming (or rejecting) your tentative identification.

Above is photo of the same two birds taken a few minutes later, with their bills showing. The left bird has a medium-short thicker bill, perfect for Red Knot. The right bird has a thinner bill that starts out straight at the base but has a slight droop at the tip, the right bill shape for Stilt Sandpiper.

These photos of a Red Knot and a Stilt Sandpiper were taken at Piute Ponds on September 21, 2014.

This was a very difficult quiz! Congratulations to Susan and Molly for identifying the Stilt Sandpiper, and congratulations to Susan and Alex for identifying the Red Knot!

–Mark