Gavia arctica
Donovan and Rees (1994) pointed out that the Black-throated Diver was a passage migrant as well as a winter visitor to Pembrokeshire. Passage has involved occasional birds flying southwards along the coastline and passing the offshore islands, mostly between September and December, although singles were recorded passing Strumble Head on 20th August 1997 and 21st August 1999 and one was at Lydstep Haven on 30th August 1988.
The number of migrants recorded has been small, with an average of nine per annum between 1983 and 2003, the most in any year being 29 in 1999. Passage has been well documented at Strumble Head, where the total between the years 1983 and 2006 is tabulated by month :
Sep - 8
Oct - 45
Nov - 85
Dec - 31
Most Black–throated Divers have departed the county by the end of March but there are 11 April records and four for May, the latest being one at Broad Haven (North) on the 25th in 1961, perhaps indicating birds passing through.
The Black–throated Diver has not been recorded in Pembrokeshire in June and July.
Graham Rees
(Covers records up to and including those for 2006)