Up to three birds were recorded in one 10 Km square during the 1981 – 1984 Winter Atlas.
The National Nature Reserve of Skomer was managed by a Warden from March to October during the Atlas years but not in the winter, when only occasional visits were made. These few visits indicated that up to 39 Barnacle Geese over wintered on the island but this information was not made available to the Winter Atlas, so is not represented on the map.
GHR
http://blx1.bto.org/atlases/BY-atlas.html