The conspicuous yellow on the breast and especially around the tail of a Grey Wagtail causes many novice birdwatchers to think they must have seen a Yellow Wagtail. However, if it's in winter and especially if it's by a stream then it will certainly be a Grey Wagtail. To identify one for certain you should look at its back: grey on a Grey Wagtail, yellowy-brown on a Yellow Wagtail. Grey Wagtails have a much longer, more black and white tail and show a broad pale wing bar as they fly over. The male in summer develops a bold face pattern with white stripes and a jet-black bib.