I think it is a stupid question. But I really cannot distinguish different kind of sandpiper. Is the one in the photo a Green Sandpiper or Grey-tailed Tattler? I think it is a Grey-tailed Tattler because in book it said Green Sandpiper look like Common Sandpiper at rest, but it don't. But on the other hand the tail of it is not grey, so it may not be a Grey-tailed Tattler. Or is it other kind? Thanks for anyone's input.
The photo was taken on 2013-09-26