Wilson's Plover (Charadrius wilsonia)
Number of individuals, sex, age, plumage: 1; probably adult
Locality:  end of 13th Street, Warrenton, Clatsop Co.,OR
Dates:  August 19,2007
Time of Day: about 11:30 
Reporting observers address: Mike Patterson
                                                1338 Kensington Av.
                                                Astoria, OR  97103
Light conditions:  partly cloudy; good visibility
Optical equipment:  25x60 Bushnell spotting scope
Distance from bird: 75 to 100 meters
Duration of observation: about 1 minute
Habitat: exposed esturine mudflat
Behavior: This was the only shorebird on the flats, though there were about 200 California Gulls with it.  I saw a largish, long-legged plover and assumed it would be a Killdeer.  When I saw it through the scope, I could see that it had only one broad, dark breast band and a large bill.  It ran along the flat in typical plover fashion.  It also did a lot of head bobbing and tail wagging (reminiscent of Spotted Sandpiper).  It disappeared behind the close sedges and cattails.  A Bald Eagle scattered everything on the flats before I could reposition myself with a camera in a spot that cleared the vegetation.
Description:  overall- clearly a plover.  Legs seemed longish for the body.
  Head- gray/brown crown, white forehead extending through the eye.  Cheek and auriculars same gray/brown as crown.  Throat white.  Bill large,black and pointy looking
  Body- Gray/brown mantle and wings, paler than adult Semipalmated, but within the pale extreme for SEPL juveniles.  Distinct, single breast band that was much dark than the mantle and coverts. Breast below band, belly and undertail coverts were white.
  Legs- longish and gray.
  I did not see the bird in flight and cannot provide details of the wings or tail.

Similar Species:  The single breast band eliminates Killdeer and plovers with incomplete or no breast band.  The most likely similar species would be Semipalmated Plover which has a short, narrow bill that is more blunt looking.  SEPL usually show little or no white past the forehead and have a much narrower supercillium.  The band below the eye is very dark in adult SEPL's and usually at least contrastingly darker than the crown in young birds.  The overall jizz of this bird was unlike a typical Semipalmed Plover, much closer in shape and proportion to a Killdeer or sandplover. 

I cannot categorically eliminate Greater Sandplover as I have not seen any and lack the references to grok the range of variation, but I'm pretty sure the breast band was too dark and the forehead and supercillium too bright.
Previous experience: I am very familiar with Semipalmated Plovers and Killdeer and have seem Wilson's Plovers in Florida.

Drawing made from memory immediately after it became clear I wasn't going to get a photo (within 10 minutes of seeing the bird).