comes to anything having to do with nature.....and certainly migratory birds fall into that category, so in this case I think it best not to say "you are NEVER going to see 15 Spoon-billed Sandpopers on an inland body of water in Washington" and just leave it as something less concrete like. "NO WAY, NO HOW, IN THIS LIFETIME, OR ANY OTHER LIFETIME, did you see 15 Spoon-billed Sandpipers on inland freshwater in Washington"....that leaves us a little "breathing room" just in case the Earth's rotation reveresed, rivers changed course and ducks migrated over the upper mid-west without Mark W seeing them........
Spoon-billed Sandpipers breed in Russia and winter as far south as the Phillipines.....depending on what you read there are fewer than a 100,000 as a high to "fewer than a 1,000 breeding pairs" as a low....Five or six records in N.A. with all but one of those being in Alaska......making the "chances" of them being the birds that you saw astronmically slim......(you didn't eat Chinese before you saw them and got a really compelling fortune cookie did you....something like....."breath today and life shall be good"......if that were the case then HELL YEAH they were Spoon-billeds cause Lord knows the only thing more reliable than "the Government is lying about duck numbers", "there are no ducks in my backyard andn THEREFORE there are no ducks anywhere", and "the migration hasn't occured", is a fortune cookie that accurately predicts something like the Sun rising or water freezing when its cold.....
My "guess" on what you saw was either Least, Western or Semi-palmated Sandpipers. All of those are little guys...6" plus a fraction or two....
The statement that I "think" the peep in the Falcon's talons was a "spoon-billed Sandpiper" was a joke....something to see if anyone was looking......
Look up Bonapartes Gull for your gull.....little guys, although a bit over twice the size of your estimate.....the Western Sabdpipers in the picture are 6 to 6-1/2 inches....little guys.....a Bonapartes Gull would be about twice that size....tiny for a gull....white with a black dot behind the eye like you describe...really small bill and delicate looking for a gull....they are common in your area in the summer, (Black Headed in breeding plumage), and you still see them in smaller numbers as long as they have open water to feed in in the winter....
What I REALLY want to see is some Redheads over the decoys....you got any of those?
Steve