Red-throated Diver – 2005

Gavia stellata – TROCHYDD GYDDFGOCH – Winter visitor and passage migrant. Recorded in every month except June

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.

Winter

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.

Age of birds

Very few observers have reported whether their sightings involved adults or immature birds, perhaps not surprisingly considering the circumstances in which they are often seen. However in the autumn it is easy to differentiate those in full summer plumage and those showing traces of summer plumage, from those in winter and juvenile plumage.

This was recorded systematically at Strumble Head during autumn passage between the years of 1980 and 2008. The proportion showing signs of summer plumage was 91 % in September, 50 % in October and 3 % in November (latest on 23 November), the total number of birds examined being 483, 588 and 533 respectively. This clearly indicates that adults pass earlier than the bulk of younger birds.   

Autumn passage

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.

Graham Rees (County bird recorder 1981 to 2007)

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

More about the Red-throated Diver in Pembrokeshire