Thursday, November 29, 2012

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 non-breeding plumage
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.