Great Northern Diver - 1949

Colymbus immer

Regular winter visitor, sometimes numerous in Milford Haven, mostly immatures.  Frequently seen near the islands and on the open coast.  occasionally remaining late in spring - a male in breeding plumage washed ashore at Saundersfoot, May 1927; and another seen Fishguard Harbour, mid-May 1930 (Bertram Lloyd)

R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society

Great Northern Diver - 1994

Winter visitor and passage migrant. Recorded in every month

Appears to have decreased since the 1940s as both Mathew (1894) and Lockley et al. (1949) stated it was sometimes numerous, particularly in Milford Haven. Dickenson and Howells (1962) noted groups of up to 20 and recorded mainly immature birds. Although 26 in a day have been seen passing Strumble Head during autumn passage, in winter there is a scattering of ones and twos around the outer coastline with occasional concentrations at favoured spots; for example, up to five have been seen in Fishguard Harbour, five in St Bride's Bay and seven in the Strumble Head tide races, with a remarkable 43 there on 6 January 1991, following prolonged gales. It is no longer numerous in the Cleddau Estuary. One or two still occur fairly regularly between Dale and Hakin, with up to five on occasions, but they rarely penetrate further up river. It is seldom seen on fresh water, with just a few records from Llysyfran reservoir and Bosherston Pools.

There is a small spring passage from March to May and a large autumn passage from September to December, birds in full summer plumage occurring particularly in May and September but sometimes in other months.

Great Northern Diver - 1980s winter atlas

 

The BTO winter atlas showed that Great Northern Divers were present in some coastal 10km squares and the outermost part of the Cleddau Estuary, during the winters of 1981-82, 1982-82 and 1983-84.

The darker the colour, the higher the relative total count for each 10km square.  The darkest blue represents over 3-5 birds.

Graham Rees 

Great Northern Diver - ages

Gavia immer

Observers have seldom included an age assessment in their reports unless noting adults in summer plumage.  

Great Northern Divers have a prolonged post breeding moult period stretching from September to January, consequently birds in summer plumage have been recorded throughout autumn passage, occasionally as late as the end of December. Of a total of 646 birds closely scrutinised passing Strumble Head in autumn, between 1981 and 2008, 48% were in full or showed variable vestiges of summer plumage.

A few birds have been recorded in full summer plumage in the spring, from late April.

Graham Rees

(Covers records up to and including 2008)

Great Northern Diver - spring passage

Gavia immer

Spring passage has been relatively small, mostly recorded as departure dates from wintering areas, normally completed by late March to early April. Occasionally presumed migrants have briefly appeared at some of these same places in late April up to 22nd May and others have been noted at or passing headlands and the offshore islands from late March to 26th May. Later occurrences were: one in the Gann – Lindsway Bay region throughout May until at least the 21st June 1991 and two at Ceibwr on 22nd June 1997. 

Great Northern Diver - autumn passage

Gavia immer

The variation in county annual totals seems to have had more to do with variation in the number of passage migrants recorded than with the number of wintering birds. Autumn passage has been noted along the coast and at the offshore islands, being most consistently documented at Strumble Head annually between 1983 and 2006.

The earliest recorded there was on 28th July 1991. August records were all of single birds, on the 31st in 1985, 24th in 1986, 28th in 1989, 23rd in 1994, 28th in 1994 and 27th in 1995. Numbers built up in September, the main passage taking place from October to December:

Totals have been grouped into six day periods, except that the last readings for October and December have been adjusted from seven day totals. This has been done by dividing the seven day totals by seven, then multiplying by six.

Great Northern Diver - winter

Gavia immer

In winter they have been found in the offshore waters all around the coast from Cemaes Head to Amroth, including Fishguard harbour.

Most sightings have been of single birds or sometimes two together, with occasionally up to seven in areas such as St Bride’s bay, Fishguard Harbour and the Strumble Head tide races. The unusual gathering of 43 at Strumble Head on 6th January 1991 was probably due to birds seeking a lee shore during a period of prolonged SW gales.

Great Northern Divers have regularly been seen within the Milford Haven / Cleddau Estuary waterway during the winter months, January to April and October to December. The average number recorded between the years 1983 and 2003 was five, the maxima in a year being 10 in 2002 and 12 in 1999, which probably included some migrants in transit.

Most records were from the area between Dale and Hakin, including the Gann, Angle Bay and the Pembroke River. Singles have been seen further upstream at Castle Pill, Llanstadwell, Neyland, Lawrenny, Cresswell and Carew Rivers, including the tidal Carew Mill Pond, Garron Pill, Beggars’s Reach,  Llangwm and Landshipping to Hook Reach area.

The only fresh water occurrences on record are of one at Bosherston 9th – 13th November 1986, two at Llys y fran Reservoir 16th January 1986, with singles there in 1983, 1984, 1985, 1999, 2001, 2002 and 2006.

Great Northern Diver - status

 Gavia immer

Winter visitor and passage migrant.

The Great Northern Diver breeds across the sub Arctic region of the Americas, Greenland and Iceland and on rare occasions has bred in Scotland and as far east as Svalbard.  Those that winter in the east Atlantic do so as far south as the Bay of Biscay and Iberia.

As with many other species, it is difficult to assess the Great Northern’s status in Pembrokeshire in the past. The accounts of previous authorities have been largely anecdotal and prone to expressions like “sometimes numerous” and “frequently seen”.

Dickenson and Howells (1962) must have felt sufficiently able to interpret the past to state “From the numbers recorded in the last decade it is possible that a decrease has taken place since the 1930’s.” The decade they referred to was 1952 to 1961, when an average of three per annum was recorded, the maximum in any year being nine in 1959.

The average recorded per annum remained at three until 1982, the maximum in a year being six in 1972. By 1983 an increasing number of observers were putting the results of their observations into the communal record and from then until 2006 the average number recorded reached 61 per annum, with the most in a year being 119 in 1999:

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 Great Northern Divers visiting Pembrokeshire.

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.

Great Northern Diver - 1894

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

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