A Spotted Sandpiper photographed at the Village Creek Drying Beds in Arlington.
Wikipedia has this to say about the Spotted Sandpiper:
The Spotted Sandpiper (Actitis macularius syn. Actitis macularia) is a small shorebird, 18–20 cm (7.1–7.9 in) long. Together with its sister species, the Common Sandpiper (A. hypoleucos) they make up the genus Actitis. They replace each other geographically; stray birds may settle down with breeders of the other species and hybridize.
Their breeding habitat is near fresh water across most of Canada and the United States. They migrate to the southern United States and South America, and are very rare vagrants to western Europe. These are not gregarious birds and are seldom seen in flocks.