Semi-mystery birds, Yellowstone in July (1 Viewer)

I just returned home tonight to California from a family trip to Yellowstone National Park in Wyoming this past week. Among the hundreds of photos I took are these of a few birds whose precise IDs eluded me. I've done my research and have my guesses, but I'd like the opinions of others. The lighting was bad in some cases, but I did my best to adjust the photos to increase clarity. Thanks in advance!

1 - juvenile Brown-headed Cowbird? (7/27/15, in burned forest along main road between Lake Village and Old Faithful area)
2-3 - Blue-winged and/or Cinnamon Teal? (7/28/15, along Yellowstone River in Hayden Valley)
4-5 - Least Sandpiper? (7/30/15, Lamar Valley along Lamar River Trail)

Least Sandpiper is right for ## 4-5.

The thick, blunt-tipped bill, relatively large head, and thick neck, among other things, suggest a juvenile Semipalmated Sandpiper for the peep.

Jim M. said:

The thick, blunt-tipped bill, relatively large head, and thick neck, among other things, suggest a juvenile Semipalmated Sandpiper for the peep.

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The yellowish legs being just muddy, then?

Agree with 1...there may be two species in the duck flock. The large bill would suggest cinnamon perhaps on the front bird. The posterior two birds ok for blue-winged? I'd prefer to see more plumage details though.

Nutcracker said:

The yellowish legs being just muddy, then?

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I don't see any yellow. Might be some mud, water, reflection making legs look not black, but semi's legs are dark green in any event.