Breeding adult has bright rusty back and crown, black belly patch, and white underparts with dark stippling. Nonbreeding adults have grayish brown upperparts, head, and breast, and are pale below. Juveniles are browner, with a scaly black and rusty brown marbled pattern above, white below, with faint stippling and trace of dark belly patch. The legs are dark.
https://www.allaboutbirds.org/guide/Dunlin/id