Motacilla lugubris
A common resident.
Mr Dix writes : " I believe we have more during the winter than in the summer. In September I noticed two or three parties of from fifteen to twenty, which, I believe, were migrating; they appeared to consist of two or three families. I have, invariably, during the winter, seen this bird in pairs, male and female, so there is 'some reason to think they pair for life. They seem particularly fond of being in a sheep-fold, seldom entirely leaving it."
Mathew M.A. 1894, Birds of Pembrokeshire and it's Islands