We visited the NH coast recently and I photographed these White-rumped Sandpiper juveniles. It may seem late to see sandpipers, but this Arctic breeding species is still migrating on the coast.
White-rumped Sandpipers have long wings with the wing-tips extending beyond the tail, a helpful ID clue. Baird's Sandpipers also have wings extending past the tail, but have a dark-centered rump. The breast and flanks on this White-rumped Sandpiper are streaked and it has a medium length, slightly down-curved bill and broad white eyebrow streak.
Another clue mentioned for White-rumped is the pale orange-brown base to lower mandible, visible in this bird, but not on all the birds we saw.
Here's another angle showing the bird poking in the seaweed for food. The long wings give this species an elongated look. You can see the white tips to the wing covert feathers. The white edges on the rusty back feathers, form lines on the upper back. The white feather edges and rusty coloring on back and head are a sign of a juvenile. The adult White-rumped Sandpiper in winter has a grayish back and wings with dark feather shafts.
Now for the best clue. This very obliging bird started to preen. Here you can see the white rump.
Here's an even better view of the rump.
Here the white rump is visible and so are the white lines on the back. We wish these White-rumped Sandpipers good luck on their long journey to South America.