Common Scoter - 1994

Winter visitor and passage migrant

Mathew (1894) stated that the Common Scoter was a "not rare" winter visitor, while Lloyd was the first to notice large numbers in Carmarthen and St Bride's bays during the 1920s and 1930s, including flocks during the summer months. Lockley et al. (1949) referred to summer flocks of up to 400 in both bays. Thereafter, many observers contributed observations which established that the Common Scoter is present in our waters throughout the year. Seawatching at Strumble Head from 1980 onwards has permitted seasonal movements to be used to interpret the overall pattern of occurrence.

Male Common Scoters generally winter further south than females (Cramp 1977). Large numbers winter in Carmarthen Bay (West Glamorgan— Carmarthenshire—Pembrokeshire), males conspicuously outnumbering females here. It is difficult to estimate how many birds are present in this huge area, but a series of aerial counts conducted by the RSPB in the 1970s indicated that over 5,000 Common Scoters were present each winter. A further 1,000-2,500 winter in St Bride's Bay where, surprisingly, males are outnumbered by females in the approximate proportion of 4:1.

The aerial surveys of Carmarthen Bay, and other counts made from boats, indicate that much larger numbers are present in March than in mid-winter, for example 25,000 between Saundersfoot and Worm's Head on 13 March 1974. This may mean that the Bay is used as a migration staging area, perhaps involving Common Scoters moving up from further south. However, apart from "over 100 passing northwards" off the South Bishop on 18 April 1976 (McCanch 1985) no visible spring movement has been detected in Pembrokeshire. It seems likely, therefore, that the main departure takes place at night. Kumari (1979) has established that Common Scoters do migrate at night, from his radar studies in the White Sea and the Baltic.

Not all leave Carmarthen Bay in the spring, presumably those remaining being non-breeders which complete their moult there. The situation in St Bride's Bay at this season is not clear. A southward passage past Strumble Head, through St Bride's Bay and then eastwards past St Govan's Head, during June and July, is thought to include males returning from their breeding grounds and making their way to Carmarthen Bay to moult. Later movements, peaking in October and November, include a larger proportion of females and these would be post-moult birds heading for their winter quarters. Fewer Common Scoters have been recorded passing St Ives in Cornwall than pass Strumble during these movements, which may indicate that our passages include birds that winter further south. The timing of the movements, coupled with a synchronous passage across the middle of England, suggests that the majority of the Common Scoters seen in Pembrokeshire are from the Fenno—Russian breeding population. A recovery of one bird in Lancashire in December that had been ringed in Finland in October supports this hypothesis, but the recovery of another that had been ringed in Iceland means that the situation may be more complex.

Common Scoters are vulnerable to oil spills and casualties were noted in 1950 and again in 1973-1974, on each occasion about 300 being found contaminated and stranded on the Pembrokeshire shoreline of Carmarthen Bay.

A male Black Scoter, subspecies americana, was at Newgale from November 1991 to March 1992 (D. Astins et al.).

Donovan J.W. & Rees G.H (1994), Birds of Pembrokeshire

Update on Monday, January 30, 2017 at 10:33AM by Pembrokeshire Avifauna committee

Black Scoter Melanitta americana is now recognised as a separate species

see article by Martin Garner