Juvenile female Western Sandpiper, Fernhill Wetlands, Forest Grove, Oregon on 18 August 2004 by Greg Gillson.
For those who venture beyond their backyards and beyond the common birds, there are several groups of birds that can present challenges in identification. Such groups include the streaky brown sparrows, some of the green warblers, vireos, and kinglets, the look-a-like Empidonax flycatchers, immature gulls, and the smaller shorebirds known as "peep" (for their peeping calls).
The Least and Western Sandpipers are common spring and fall migrants throughout the Pacific NW. They cover mudflats on bays along the coast, but also at inland puddles with drying mud edges in the dry autumn heat.
Identification separating these two is fairly straight forward, as the Least Sandpiper has yellowish legs and the Western Sandpiper has black legs. However, in the fall the plumages are confusing, as there are adults in boldly streaked brown breeding plumage early in the season (July and August) fading and wearing gradually to dull tan, until molting into the gray and white non-breeding plumage in October. Then, the bright brown and rusty and white-edged juveniles are present from August through October.
In the flocks of fall migrant shorebirds, each in slightly different plumage, may lurk an exciting vagrant rare bird for the careful observer, or an identification trap for the unwary. New identification criteria, better field guides explaining the differences, and a better understanding of migration timing for some of the rare vagrants have revealed some patterns. This has led to the discovery that Semipalmated Sandpipers are regular migrants through the Pacific Northwest in small numbers.
The typical juvenile female Western Sandpiper is pictured above. Juveniles have bright, crisp feathers of the upperparts. These are often black centered with broad, clean edges of white, yellow, tan, or rusty. You can see above that all the brown feathers of the wing are edged in cream with some dark shaft streaks. The feathers of the shoulders (scapulars) are rusty-centered with black anchor-shaped subterminal marks, and white tips. The legs are black. The bill is longer than the head, thick at the base, and tapers and droops gradually toward the tip.
Semipalmated Sandpipers have short, straight, blunt-tipped bills. But don't be fooled by looking at only this one field mark. While there are certainly more Semipalmated Sandpipers out there than we used to think (the majority of Semipalmated Sandpipers migrate down the East Coast), it is my contention that many birders are misidentifying small-billed male Western Sandpipers as the rare Semipalmated Sandpiper in the West.
Take a look at the bird photographed below. It has black legs and a rather straight, short bill compared to the bird above. Is this a Semipalmated Sandpiper?
Juvenile male Western Sandpiper, Newport, Oregon on 7 August 2009 by Greg Gillson.
No, the bird above is not a Semipalmated Sandpiper. It is a juvenile male Western Sandpiper. Males of many shorebirds have smaller bills (and other measurements) than females. Again, notice the bold, crisp upper part feathers with wide colored edges. This indicates a juvenile. The scapulars are rusty cinnamon in color, just a touch redder than expected on the brightest-colored Semipalmated Sandpipers. The bill has a narrower "pinched" look just before a slightly broader tip--a kind of small "blob" at the end of the bill.
Now compare this bird with a Semipalmated Sandpiper (below) found in the same flock.
Juvenile Semipalmated Sandpiper, Newport, Oregon on 7 August 2009 by Greg Gillson.
The bird above is in very fresh plumage. The hint of buff across the breast is on the very tips of the breast feathers and will soon wear off to become entirely white breasted. The wing feathers are crisply edged, indicating a juvenile. But note the the subterminal anchors are more brown than black as the Western Sandpiper. The edges are more cream than white. This gives the bird less contrasting look, dark brown and cream rather than black and white. Notice that a few of the scapular feathers are pinkish, but not really deep rusty. And look at that bill. It really is stout, without any droop or constriction just before the tip.
If you are at the stage of your birding development where you are attempting to identify shorebirds, I suggest the following. Get a copy of Advanced Birding, a Peterson Field Guide by Ken Kaufman (1990). Start in spring when there are no juveniles, only bright adults in breeding plumage. Finally, take a shorebird class offered by the larger Audubon Societies (The Audubon Society of Portland regularly teaches such classes for free or nominal charge). Finally, go shorebirding in fall with expert birders. It is of utmost importance to identify juveniles. If your expert can't explain the various feather tracts and changes that identify a bird as a juvenile, they are not really an expert, even though they may be able to properly identify most of the shorebirds they see. Finally, really study and look at the birds you see. Take notes, take photos, compare to the field guides. Go back out again to pay attention to a mark you may have missed earlier. Practice, practice, practice!