Larus hyperboreus - irregular winter visitor
The number of individuals records per year - as the birds move around, it isn't always possible to be absolutely certain of the number of individuals involved. Some birds stay for long periods, eg one at Llanstadwell from 20 Feb 1993 to 15 Jan 1995, allowing observers to monitor plumage changes.
2014 and 2017 were good years in Wales for this species, though for the latter year, this is not obvious in the county records.
Records extracted from the Pembrokeshire Bird Reports