In the winter, they are all white underneath. Some of the best field signs are the fact that it’s a pretty chunky bird with a black, straight bill and black legs. They’re 7-8″ long; about the size of a Dunlin. They lack back toes, but that can be hard to see if they’re running along. I find one of the most reliable field signs to be that dark shoulder patch which is visible in both breeding and non breeding plumage. Right now, in December, they look like this: