Motacilla alba yarrellii
Numerous breeder, and nesting on most islands (Ramsey, Skomer, Skokholm, Caldey, not Grassholm). Roost of 600-1000 in gorse at Martletwy, Jan-March 1935. Also regular and numberous autumn passage migrant.
R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society