Balearic Shearwater - Analysis of Strumble Head records

Puffinus mauretanicus

From one to five birds per occasion were recorded from Skokholm, Skomer, Grassholm, Ramsey,

Whitesands Bay, St David’s Head, Fishguard Bay, St Govan’s Head, from the Rosslare to Fishguard ferry and in the Celtic Deep area. However intensive watching at Strumble Head revealed a greater presence in local waters than observations elsewhere hitherto suggested.  

The annual totals are probably over-estimates as they would include individuals remaining in the observation area for more than one date. Unlike most other seabirds which are generally seen passing north to south through local waters in the autumn, Balearic Shearwaters arrive from the south in search of food and are often seen feeding offshore.

Hours of observation

 

The number seen has varied from year to year.  The hours of observation compared with birds seen indicates that this was not just a consequence of observer effort. The trend over the 23 year period was of increase.

This was part of an increase noted throughout south west Britain at this time, demonstrated by Wynn and Yesou (2007), which was probably due to a warming of the sea surface causing small fish shoals, the prey of this species, to move  further north than in the past.

Most were recorded between July and November, the largest numbers between August and October. Counts at Strumble Head have usually consisted of one to six birds per day but rising to about 20 when strong northerly winds blew. Higher counts of 33 on the 4th October 1996, 36 on the 2nd October 1999, 37 on the 22nd September 2003 and the maximum recorded of 93 on the 7th October 2006, occurred when there were strong northerly winds, which pushed birds closer inshore than they might otherwise have approached. Exceptional numbers of Balearic Shearwaters were seen in the waters of south west Britain including Wales, in the autumn of 2006.

Patterns of occurrence at Strumble Head: total numbers.

 There have been a few sightings outside the July to November period: once at the Smalls in December 1984 and January 1983, 10 times in eight different years at Strumble Head in December and 10 times in four years in January. None have been recorded in March but singles have been noted at Skomer on the 25th April 1991, at Skokholm on the 15th May 1997, from the Fishguard to Rosslare ferry on the 25th May 1997, near Grassholm on the 2nd June 1993, off Strumble Head on the 2nd February 2002, 16th April 1990, 2nd June 1993, 2nd June 1996 and 8th June 1987. 

From time to time observers have pointed out that some shearwaters seen in Pembrokeshire waters resemble Yelkouan Shearwater. Other observers considered these birds could be particularly pale Balearic Shearwaters. Those breeding on Manorca would appear to exhibit mixed characteristics of both Balearic and Yelkouan Shearwaters, further clouding the issue.

Graham Rees

(Covers records up to and including 2006)

References

WYNN. R. And YESOU. P. 2007. The changing status of Balearic Shearwater in northwest European waters, British Birds, Vol. 100, 392 – 406.

Balearic Shearwater - Status

Puffinus mauretanicus

Status: annual visitor.

Balearic Shearwaters are only known to breed on the Balearic Islands in the western Mediterranean. There is a known breeding population of only 2,000 – 2,500 pairs, which makes it one of the most vulnerable seabirds in the world. Post breeding dispersal has regularly resulted in a proportion visiting the Bay of Biscay and south-west Britain and Ireland.

A specimen housed in the Museum of Comparative Zoology, Harvard, USA, collected in Pembrokeshire waters in September 1900, was the first to be recorded in the county.

 It was next recorded when one was seen from a boat near The Smalls on the 7th July 1955. Balearic Shearwaters were then noted in 11 years between 1960 and 1975 and annually from 1980.

Manx Shearwater - 1894

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

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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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Great Northern Diver - 1894

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

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Black-throated Diver - 1894

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

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Red-throated Diver - 2005 status

Gavia stellata

Winter visitor and passage migrant.

The Red–throated Diver has a circumpolar Arctic breeding distribution, the nearest nesting to Pembrokeshire being in Scotland. Those on the eastern side of the Atlantic winter southwards to the Bay of Biscay, sometimes entering the Mediterranean.

Mathew (1894) and Lockley et al (1949) considered the Red-throated Diver to be a common winter visitor. The former gave no actual counts and the latter noted only a group of 20 off the west coast and 15 off Giltar Point.

Bertram Lloyd (1939) recorded all the Red–throated Divers seen during his intermittent visits to the county during the period 1929 – 37.  The places he saw them coincided with localities where they were noted in the 1980’s and 1990’s, as did the numbers involved. This led Donovan and Rees (1994) to think that perhaps this diver’s status had not changed in the previous 60 years or so.

Dickenson and Howells (1962) commented that almost every winter small numbers of Red–throated Divers had been seen off both the west and south coasts of Pembrokeshire, from mid October to the end of April. That they had been recorded within Milford Haven and Fishguard Harbour and that R. M. Lockley had told them that he recorded them frequently on his winter journeys from Skokholm to the mainland between 1927 and 1940. They went on to note that from the numbers recorded in the last decade it is possible that a decrease had taken place since the 1930’s.

The average number recorded in the 1930’s was 10 per annum which included 43 noted in 1930. The average recorded from 1952 to 1961, the period covered by the Dickenson and Howells review, was only 5 per annum, the most in any year being 10 in 1961.

The average on record for the years 1963 to 1982 was 6 per annum, the maximum in any year being 23 in 1973. How much credence can be put into these statistics being representative of the true picture is brought into question, when considering that in the period 1983 to 2002 an average of 225 per annum were put on record, the largest total in a year being 394 in 2001.

There was a marked increase in the number of active observers during the 1980’s and 1990’s, they possessed ever improving optical aids and most had the discipline to contribute their observations to the communal record. These are likely to be the factors that explain the upsurge in records, rather than there being an increase in the number of Red–throated Divers visiting Pembrokeshire.

TOTALS RECORDED 1983 – 2005

These totals have been calculated by summing the maximum for each locality in each season and the number seen visibly migrating. They do not attempt to assess any possible turnover in numbers at specific sites and the migrant totals would have been influenced by the amount of time spent watching from headlands and islands. It is likely therefore that the totals represent the minimum presence in local waters.

References

DICKENSON. H and HOWELLS. R. J. 1962. Divers in Wales, Nature in Wales 8.

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

LLOYD. B. 1929-1939 Diaries, National Museum of Wales.

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

Red-throated diver - winter

Gavia stellata

Red – throated Divers have been recorded all around the outer coast in winter, normally 1 – 10 at most localities but some places have been more favoured, where up to 50 have sometimes been recorded , such as the Strumble Head tide races, various parts of St Bride’s Bay and off Amroth.

They have also shown an ability to temporarily accumulate at what were presumed to be good food sources and hence demonstrated a great deal of mobility within the region. Occurrences of this nature were up to 75 at Goultrop Roads 1st – 19th January 1996, 60 there on 19th January 1997, up to 40 in January 1998, peaking at 85 on the 23rd, 60 on 16th December 1998 decreasing to 22 by 31st December. A similar attraction was noted at Amroth in 1993 when 200 were present on 20th February, decreasing to 25 by 27th February but then 145 there on 6th March.

Mathew (1894), Lockley et al (1949) and Lockley (1961) emphasised the importance of the Milford Haven waterway for Red – throated Divers. Post 1961 none were recorded there until 1981, since when they have been noted in 18 years, up to 2006.

Most records have involved single birds, occasionally two together, with three at the Gann on 1st April 2006, six Monk Haven/ Gann area 3rd – 19th January 2003 and seven Dale Roads on 10th February 2002. All records refer to the region between Dale Roads, Angle Bay and South Hook Point, save for singles at Picton Ferry 17th January 1981, Llangwm 12th October 1992, Carew-Cresswell 12th December 1993 and 10th March 1985, Garron Pill 20th March 1997 and five Carew River on the 5th December 1982.

The Red – throated Diver is predominantly a marine species in Pembrokeshire, with just four singles being recorded on fresh water, viz. Bicton Reservoir 9th April 1967, Hayston Hall November 1985 and Llys y fran Reservoir 21st December 1993 and 16th January to 22nd February 1986.

Red-throated diver - passage

Gavia stellata

A marked autumn passage of birds travelling from north to south has been recorded since at least 1980, spanning the months August to December, though singles were recorded in 2 years on the 11th July and once on the 3rd July.

This movement has been well documented at Strumble Head. August records were confined to the latter part of the month, 19th – 31st, totalling just six birds over the period 1980 – 2006.The main passage was between October and December and is represented below in graphical form. These are the mean annual values calculated from the total number of birds recorded for the period 1980 to 2006, grouped into six day intervals.

Only once in 27 years did the passage continue into January, when 40 passed on the 6th in 1991, thereafter no movement being detected during that month. The number of birds passing on any one day was generally small but over 30 was recorded five times in four different years, the maximum being 44 on the 4th December 1993.

The December peak was obscured in some years, with passage ceasing during gales. It is not known whether these held up birds within the comparative shelter of Cardigan Bay which continued their migration when the wind moderated, or the gales displaced birds from further south to seek shelter in the Bay, or possibly whether both reactions took place.

A passage of smaller volume than in the autumn has been noted in spring, March to 30th May. This has not been well documented but has involved birds passing westwards off St Govan’s Head, northward past the offshore islands of Skokholm and Skomer and eastwards past Strumble Head.

The Red – throated Diver has only been recorded in Pembrokeshire once in June, when two were seen at Skomer on the 18th in 2003.