Dave, Sanderlings have the entire lesser coverts blackish. This dark area
can be hidden when the wing is folded, but it can also be exposed and very
conspicuous (perhaps during aggressive interactions). Juvenile wings look
the same as adults. My hypothesis for your bird might be droopy-wing
syndrome (bird is sick, tired, bored?).

Dennis Paulson phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416