Stilt Sandpiper - In its boldly barred breeding plumage, the Stilt Sandpiper is easily identified. In its gray non-breeding plumage, it is much less distinctive and appears to be intermediate between a yellowlegs and a dowitcher.

Adult Description:
Medium-sized sandpiper. Long, greenish legs. Long neck. Long bill, drooped at the tip. White rump. Gray tail. Wings plain, without white stripe. Breeding plumage heavily barred on the underside, with dark blotches on the back, and chestnut cheek patch. Non-breeding plumage all gray on back with lighter belly.

Immature Description:
Juvenile similar to non-breeding adult, but browner, with scaly back with light edges to feathers, and thin streaks on chest.

Lesser Yellowlegs has mostly white tail, bright yellow legs.

http://www.allaboutbirds.org/guide/Stilt_Sandpiper/id 

http://10000birds.com/another-visit-to-jamaica-bay.htm

By now you have already seen the images of Pectoral Sandpipers and
Wilson's Pharalope from my last trip onto the East Pond of Jamaica Bay
Wildlife Refuge.  You have also, I am sure, suffered through my Ode to
Mud, inspired by that same visit.  But you have not seen any of the
other images I got during the eight hours I spent exploring the refuge
on a hot summer day.  Yeah, this is the lazy blogger's route, but I'm
going to just post up my favorite pictures from the last visit that I
haven't already used, just so you can appreciate some more of the
wonderful birds that use the habitat at the best wildlife refuge on the
east coast.

Stilt Sandpipers (shorter neck) looks similar to yellowlegs (long neck).

http://10000birds.com/wp-content/uploads/2010/08/jam-bay-lesserlegs.jpg

http://10000birds.com/wp-content/uploads/2010/08/jam-bay-stilts.jpg

http://10000birds.com/wp-content/uploads/2010/08/jam-bay-stilts-2.jpg

Juvenile Stilt Sandpiper with Lesser Yellowlegs juvenile

http://www.ofo.ca/photoalbums/checklist/Sandpipers_Phalaropes/Stilt%20Sandpiper/slides/DC_Stilt_Sandpiper_5092_01.html

 

Juvenile (front) with Lesser Yellowlegs juvenile<br>

Stilt Sandpiper (Calidris himantopus). Juvenile (front) with Lesser Yellowlegs juvenile. Photo by Daniel Cadieux.