Mergus serrator – HWYADEN FRONGOCH – Winter visitor
The BTO winter atlas showed that Red-breasted Mergansers were present in some coastal and all estuarine 10km squares during the winters of 1981-82, 1982-82 and 1983-84.
The darker the colour, the higher the relative total count for each 10km square. The darkest blue represents 6-18 birds.
Graham Rees. Pembrokeshire County Bird Recorder 1981-2007
Data collected by volunteers for the BTO. Lack, P. 1986 Atlas of wintering birds in Britain and Ireland. T & A.D. Poyser.