Uria aalga – GWYLOG – Breeding resident, passage migrant and winter visitor
|Breeding possible||excluded from total|
|No of tetrads occupied||17 (of 478)|
|Percentage of tetrads||3.6%|
Both Mathew (1894) and Lockley et al. (1949) reported that Guillemots nested on all of the islands and at various mainland cliffs. Egg collecting used to be prevalent; Howells (1968) noted that Ivor Arnold took 500 Guillemot eggs from Ramsey in 1908.
It is difficult to census Guillemots accurately as the number of birds present on the breeding ledges varies with the season and time of day. A single count does not necessarily equate with the number of nests present. However, Lockley (1958) estimated that 5,000 Guillemots were present on the Skomer cliffs, resolved as “approximately that number of pairs”. The same assumption has apparently been made by many other observers over the years. This means that the numbers quoted here should not be taken literally, though they should be comparable enough to detect broad trends.
Lockley et al. (1949) noted a decrease in numbers during the second World War and Lockley (1958) used photographs of the occupied ledges at the Wick, Skomer, taken in 1939, 1946 and 1958 to demonstrate a further decline. He was inclined to attribute the decrease to fouling by oil pumped from passing ships. Numbers continued to diminish and the Operation Seafarer survey of 1969 revealed just over 6,000 pairs. They were dealt a further blow by the Irish Sea seabird wreck that same autumn: 15,000 dead or dying Guillemots were accounted for in the Irish Sea but many more must have gone undetected, and Saunders (1976) speculated that as many as 35,000 could have perished. The effects can be judged by a decrease at the Skomer colony from 5,000 in 1966 to 3,000 in 1974.
Pembrokeshire numbers appear to have stabilised during the 1970s and to have increased since, despite temporary setbacks caused by oiling during the wrecks of the Christos Bitas (1978) and the Bridgeness (1985). The Seabird Register survey of 1985-1987 assessed the total county population as about 14,000 pairs, the main colonies being at Skomer (6181), Elegug Stacks, Flimston (3,462), Ramsey (1757), Stackpole Head (980) and Skokholm (160).
Although Guillemots continue to increase conservationists are concerned about disturbance that could be caused by an increasing popularity of rock climbing, particularly on the limestone of the southwest peninsula. The exploration for and possible extraction of oil and gas from our adjacent sea areas also poses potential threats.
Young Guillemots leave the breeding ledges before they are able to fly. The single chicks are accompanied by males and swim to traditional feeding areas, presumably where suitable fish are plentiful. Whilst the young are growing to the fledging stage the adults moult into a state of flightlessness. Only one such regularly used area has been found off Pembrokeshire to date, the sea off Strumble Head, where 300-500 gather each year. After fledging/moulting Guillemots become very mobile. Ringing has shown that while some remain in Pembrokeshire waters other adults journey to Scotland and immature birds into the English Channel, to the North Sea, to France and Spain and into the Mediterranean.
One of the great spectacles of the autumn is the large passage of line after line of Guillemots speeding low across the sea on their way out of the Irish Sea past the north coast of Pembrokeshire between late September and early December, first recorded by Lloyd as long ago as 1936. In more recent times attempts have been made to estimate peak numbers by taking sample counts for 15 minutes in each
hour and extending the results over the duration of the movement. By such means totals of 24,000 were calculated to have passed Strumble Head on 17 October 1983, 26,000 on 13 November 1987 and 35,000 on 20 October 1984.
Small numbers are scattered around the bays and tide races of the coast during the winter, with increased numbers during onshore gales. Large numbers occasionally visit the colonies on fine days in winter when they noisily occupy the ledges and take to the wing for massed whirling flights.
Northern Guillemots subspecies aalge/ hyperborea have been detected on several occasions at passage times and during the winter.
LOCKLEY, R.M. 1958. Sea Birds and their Protection. Bird Notes 28:380-383.
SAUNDERS, D.R. 1976. A brief guide to the birds of Pembrokeshire. Five Arches Press.