Black-necked Stilts are always fun birds to see. The black-white contrast is striking on top of the tall spindly red legs. Based on the animated eBird maps below of Black-necked Stilt sightings, it confirms my experience that they are early migrants. They arrive in Idaho in April and leave in September, whereas most migrants are arrive in May and leave in October.
Below is AllAboutBirds.com's range map. Looks like that stretch on the Mississippi River will have to be added.