Western Sandpiper or Dunlin? Winter ID challenge

Dunlin, October 3, 2004. Forest Grove, Oregon by Greg Gillson.

Both Western Sandpipers and Dunlins can be abundant at times in the Pacific Northwest. In breeding plumage you would never mistake one for the other. From late fall through early spring, however, when both species are in drab non-breeding plumage, with long drooping bill and black legs, many birders have trouble separating them.

A very general statement of status in the Pacific NW follows. Western Sandpipers are abundant spring and early fall migrants throughout, with a few wintering along the immediate coastline and Puget Sound. Dunlins are abundant spring and late fall migrants, and common winter visitors wherever there is open water and wetland shores coastally or inland.

The problem with mistaken identification occurs from November through March when primarily only Dunlin are expected inland. Even in larger bays on the coast and the shores of Puget Sound, where a few Western Sandpipers may be found in winter, Dunlin are far more numerous than Western Sandpipers, November through March. Reports of large flocks of Western Sandpipers inland during the winter are likely in error, though singles do occur from time to time, west of the Cascades. There are going to be occasional exceptions to the status stated, but this warning is one to follow: be careful identifying Western Sandpipers after early October (and until early April) in the Pacific Northwest--they are much more likely to be Dunlin.

Western Sandpiper, September 6, 2008. Forest Grove, Oregon by Greg Gillson.

The accompanying photos show juvenile Dunlin and Western Sandpiper mostly molted into their nonbreeding plumage. Now Dunlin are bigger, 8-1/2 inches long compared to 6-1/2 for Westerns, but that's not always apparent if there is nothing to compare with. Least Sandpipers are barely smaller than Westerns, and may be found more regularly in late fall and winter. So if there are any of those present, Dunlin will look much larger. Killdeer should appear approximately twice the size of Western Sandpipers, while Dunlins should be about 2/3 the size of a Killdeer.

Dunlin appear rather smooth brownish-gray throughout, including the head and across the breast. They appear almost hooded.

Western Sandpipers are paler gray and a bit more streaky and contrasty on the crown and back, with white throat and breast with perhaps a few streaks coming down from the shoulder. The pale eyebrow and face contrasts with darker ear coverts.

In flight both are similar in appearance with thin white wing stripe on the tips of the greater secondary coverts, and drooping bill. The voices aren't so different that you'd notice right away and remember. So pay special attention to the throat and breast. And remember... Dunlin are more likely in winter than Western Sandpipers, especially inland.

Western Sandpiper

Western Sandpiper, Gearhart, Oregon, 6 August 2011 by Greg Gillson.

 

In the winter, flocks of small sandpipers chasing the waves in-and-out on the beach are likely to be Sanderlings. However, during spring and fall migration, nearly any shorebird may be found on the beach.

These "peep" (small sandpipers in the genus Calidris, named for their peeping calls) are Western Sandpipers.

I took this photo near sunset while on a picnic at the beach this summer.

What else can we learn from this photo above?

The sandpipers have partial webs between the toes that you can see in these photos as a wedge at the base of the toes. The presence or absence of this feature is important to note for identifying certain rare Asian stints (name of peep in Europe and Asia) that show up from time to time in the Pacific NW. The abundant Least Sandpiper has unwebbed toes--practice seeing this field mark with these two common species so you are better prepared when something unusual shows up!

Sanderlings do not have hind toes. You can clearly see the small hind toe on the one raised foot of the Western Sandpiper above.

There are three bright, colorful, and crisply-plumaged juveniles on the right, one disheveled dull-backed adult on the left with chevrons on the sides of the breast. Most adults start migrating back to the wintering grounds several weeks before the juveniles. This photo was taken during the period of overlap in early August.

 

Juvenile Western Sandpiper, Gearhart, Oregon, 6 August 2011 by Greg Gillson.

 

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ID challenge... Western Sandpiper and Semipalmated Sandpiper

ID challenge... Western Sandpiper and Semipalmated Sandpiper

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!