Chlidonias niger – Cors-wennol Ddu – Annual passage migrant.
The Black Tern has a widespread breeding range embracing the North Americas, Europe and Western Asia. Most of those seen in Pembrokeshire probably originated in Scandinavia, Poland and the western region of the former Soviet Union. Birds from this area migrate to winter along the western seaboard of Africa, where they are mostly coastal and pelagic.
Mathew (1894) mentioned just two undated records for the county and Lockley et al (1949) added just one more, shot at St Davids in September 1904. Black Terns were recorded 19 times between the years of 1949 and 1980, involving a total of 53 birds, the maximum in a year being 12 at Skokholm on the 8th September 1958. Post 1980 the Black Tern proved to be a regular autumn passage migrant in variable numbers.
Records came from the Teifi Estuary, Nevern Estuary, Fishguard Harbour, Newgale, Broad Haven (North), several places within the Cleddau Estuary, Manorbier, Tenby, around the islands of Ramsey, Skokholm, Skomer and Grassholm, from the Fishguard to Rosslare and Pembroke to Rosslare ferries and over fresh water at Bosherston and Newgale Marsh. However the majority, 94 %, were seen at the intensely watched Strumble Head.
Annual total number of birds, 1981 – 2006.
Autumn records spanned from the 8th August to the 11th November, 95 % of them between the 14th August and the 8th October. In some years few were seen, in others larger totals, especially when peak numbers passed in one or two days, as 100 on the 12th September 1981, 98 on the 14th August 1985, 112 on the 27th August 1997, 86 over the two days of the 24th and 25th August 1999, 97 on the 8th October 2001, 536 on the 31st August 2005 with 117 on the 1st September 2005.
The peaks occurred during brief periods of light to brisk southerly winds, particularly from the south east, accompanied by low cloud and mostly with rain or drizzle. On those occasions the terns flew in from out to sea flying directly into the wind. When nearing the shore they mostly turned westwards, which enabled them to continue out to sea but some turned into Cardigan Bay. On the 31st August 2005 groups approaching the land bunched into tight formation and climbed rapidly, almost vertically, to disappear from sight into the low cloud cover. It seems likely they continued on their south east heading, going overland. BWP notes that Black Terns sometimes migrate at considerable height and the beginning of such action was probably witnessed at Strumble Head that day.
Very few Black Terns have been recorded in Pembrokeshire in spring, viz. one at Dale on the 8th May 1954, two Teifi Marshes on the 7th May 1986, one Gann 19th April 1987 with three at nearby Anchor Hoaten the same day, one Skomer 24th April 1988, two Garron Pill 3rd May 1988 with one remaining for the next day, singles at Pembroke Mill Ponds 25th April 1988 and St Govan’s Head 20th April 1992.