Arctic Skua - Age and morph

Stercorarius parasiticus

Age and or morph was recorded for the bulk of the Arctic Skuas seen at Strumble Head between 1980 and 2006. Adults made up 67 % of the total, of which 31 % were light–phase, 33 % dark–phase and 3 % classified as intermediates, the remaining 33 % of the total were predominantly juveniles, though some first and second year birds were identified.

Graham Rees.

(Covers records up to and including 2007).

Arctic Skua - Spring

Stercorarius parasiticus

The Arctic Skua has been sparse in Pembrokeshire waters during spring, with one to three per annum being the norm during the period 1958 to 2003, passing between the 4th April and the 30th June. Four in 1998, six in 1996, eight in 2002 and 10 in 1993 exceeded the norm. Records came from Tenby, Broad Haven (S), St Govan’s Head, West Blockhouse, St Ann’s Head, Skokholm, Skomer, The Smalls, St Bride’s Bay and Strumble Head.

Graham Rees.

(Covers records up to and including 2007).

Arctic Skua - Autumn

Stercorarius parasiticus

The number of birds involved each autumn varied, extremes being 67 in 1993 and 355 in 1985. Differing breeding success no doubt played a part in this variability but changing weather systems seem to have been the main factor.

Autumn totals at Strumble Head, 1980 – 2007.

 Passage has been recorded from July to December, at Strumble Head between 1980 and 2006, a total of 24 being seen in July, 32 in November and 5 in December. Totals for the months August to October, expressed in six day periods were:

Light to moderate winds with a westerly component prevailed in most autumns. It was thought that some of the Arctic Skuas travelling southwards through the Irish Sea were drifted eastwards into Cardigan Bay by these westerly winds. When the skuas encountered the north Pembrokeshire coast they followed it in a westerly direction, so as to gain sea room for their continued southward migration. When south–westerly gales occurred larger numbers appeared in Cardigan Bay, presumed to have been blown there from the sea area south of the Irish Sea. When the wind veered to between west and north before moderating, these birds were able to make their way back out to sea, many of them passing close in to Strumble Head. It was such a weather system that resulted in the largest day total recorded when 103 passed on the 3rd September 1983.

Light to moderate north–east winds predominated in the autumn of 1993 and few Arctic Skuas were seen, most of those that did pass were during short interludes of westerly winds. Strong winds from due east dominated the autumn of 2003 when a total of 203 Arctic Skuas was logged passing. Such winds could be expected to drift southward travelling birds away from Cardigan Bay, so it seems likely that those seen at Strumble Head had arrived by flying overland from the North Sea assisted by the following wind.

Observational evidence indicates that Arctic Skuas are diffusely spread once they have cleared the north coast of the county. Daily observations from The Smalls throughout the autumns of 1983 and 1984 recorded far fewer birds than passed Strumble Head on the same dates. Offshore watchers using boats going as far out as the Celtic Deep only occasionally encountered one or two Arctic Skuas, as was the case with shore based watchers on the west and south coasts of the county and on the offshore islands. At Skokholm the mean autumn total from 1953 to 2003 was seven birds.

 Graham Rees.

(Covers records up to and including 2007).

Arctic Skua - Status

 Stercorarius parasiticus

Passage migrant.

The Arctic Skua has a circumpolar Arctic breeding distribution extending southwards to northern Scotland. Migrants seen passing through British waters are en route to and from Atlantic wintering areas, principally south of the equator.

Mathew (1894) noted just one record of an Arctic Skua, shot at Goodwick, but gave no date. Lockley et al (1949) considered it to be occasional off Skokholm and Grassholm, mainly in August and September but sometimes in May or June.

A mean of 10 per annum was recorded in the county between 1953 and 1975, during a period when little seawatching was conducted. The low detection rate being linked to a paucity of watching was emphasised when Saunders (1976) noted 45 passing Strumble Head on the 8th September 1974. Watching at this headland became more frequent from 1978, with regular autumn observations from 1980 onwards. The annual average total of Arctic Skuas recorded in Pembrokeshire between 1980 and 2003 rose to 235, 90 % of them being seen at Strumble Head, passage taking place between July and November, the majority between August and October.

Graham Rees.

(Covers records up to and including 2007).

Pomarine Skua - ageing and morphs

Stercorarius pomarinus  

Age and or morph was recorded for most Pomarine Skua sightings. Fewer adults than other ages were recorded. Adults made up 37 % of the total in the Strumble Head series between 1982 and 2003.

 When the highest day totals were recorded, on the 17th October 1991 and on the 18th October 1991, during a recovery movement in strong north–west winds, following south–west gales which had presumably displaced unusually high numbers into Cardigan Bay, only 25 % and 18 % respectively were adults, suggesting immature birds were more susceptible to the immediate effect of extreme weather.

Light- phase made up the bulk of the adult sightings, dark-phase birds amounting to less than 1% of the total.

Graham Rees

(Covers records up to and including 2006)

Pomarine Skua - spring passage

Stercorarius pomarinus

The Pomarine Skua has been of erratic occurrence in spring, involving small numbers between the 8th April and the 18th June. Singles have been recorded from Caldey, St Govan’s Head, Skokholm, Skomer, Grassholm, The Smalls, Druidston, Newgale, Ramsey and Strumble Head, with two together at Amroth on the 4th May 2003 and a party of five passed Skokholm on the 28th May 1991.

One seen at The Smalls on the 28th February 1983 may have been an early migrant or possibly over wintering in the general sea area.

Graham Rees

(Covers records up to and including 2006)

Pomarine Skua - autumn passage

Stercorarius pomarinus  .

The Arctic breeding range of the Pomarine Skua is almost circumpolar, being mainly correlated with the variable distribution of Lemmings. Migrants seen in north-west Europe are en route to or from wintering areas off west Africa, which lie largely north of the Equator.

The Pomarine Skua was first recorded for Pembrokeshire by Mathew (1894), who commented “a few are to be seen every autumn, and after heavy gales large flocks are observed.”  Lockley et al (1949) considered he could have been wrong, as they knew of only four occurrences during their time, the only one dated being on the 21st September 1930.

There were seven records involving 11 birds during the next 28 years. With the exception of 1979 they have been recorded annually since 1976. Most were seen in the autumn, between August and December and predominantly at Strumble Head.

 

N. B. The discrepancy between the 1991 total and that given by Donovan and Rees (1994) is because of additional records received since publication of that work.

Totals August to November 1980 – 2006.Values are expressed in six day intervals, the last period in months of 31 days have been adjusted from seven day totals by dividing by seven and multiplying by six.

Daily totals were small, normally involving less than 20 birds, with the following exceptions: 22 on the 20th October 1984, 30 on the 10th November 1985, 59 on the 7th October 1988, 97 on the 17th October 1991, 130 on the 18th October 1991, 20 on the 4th September 1992, 24 on the 20th October 1999, 27 on the 6th November 1999 and 21 on the 4th December 1999.

There were only six other bird days recorded in the month of December over the whole period from 1980 to 2006, the latest being on the 27th in 1990 and 1999. Early occurrences were of single birds on the 21st and 22nd July 1990 and 24th July 1998.

Away from Strumble Head, autumn records of one to four birds were noted off Fishguard, from the Fishguard to Rosslare ferry, Ramsey, Newgale, The Smalls, in the Celtic Deep, Skomer, Skokholm, St Govan’s Head and Amroth, with 11 at St David’s Head on the 5th November 1999.

Graham Rees

(Covers records up to and including 2006)

References

DONOVAN. J and REES. G. 1994. Birds of Pembrokeshire, Dyfed Wildlife Trust.

LOCKLEY. R. M, INGRAM. C. S. and SALMON. H. M.1949. The birds of Pembrokeshire, West Wales Field Society.

MATHEW. M. 1894. The birds of Pembrokeshire and its islands, R. H. Porter

Pomatorhine Skua - 1894

Species account from M Mathew, 1894, "The Birds of Pembrokeshire and its islands"

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