White Wagtail
These breed in Iceland and Continental Europe. The Pied Wagtail is the common wagtail in the British Isles. The only time White Wagtails are seen in Ireland is on spring or fall migration when they transit Ireland on their way to or from Iceland.
Canon EOS-1D X, f/5.6 @ 360 mm, 1/500, ISO 100, No Flash
T.Michael Redmond