Bewick’s Swan Cygnus columbianus bewickii [Yarrell, 1830]
WWT Slimbridge, Glos. © Nigel Milbourne 2007
Scarce, passage migrant & winter visitor. May occur between November & March.
The Tundra Swan C. columbianus has two recognised subspecies, the Whistling Swan C. c. columbianus (a native of North America where it was known as the Tundra Swan until the 1980s) and Bewick’s Swan C. c. bewickii (which breeds on Russian tundras). There are three recognised populations of Bewick’s Swan which follow different migratory flyways to winter in north-west Europe (the northwest European population), the Caspian Sea (the Caspian / west Siberian population) and China, Korea and Japan (the eastern population). While there is some evidence that the swans may switch flyways on occasion, it is reasonable to expect birds that appear locally to be from the northwest European population that breeds on the open maritime tundras of European Arctic Russia. These birds migrate 3-4000 km west along the Arctic coast of Russia, then south west over Karelia and along the Baltic coast, to winter in western Europe. In January 2005, it was estimated that the north-west population numbered 21,500 birds and despite an increase in Britain during the second half of the twentieth century, there has been a recent decrease of 46% in numbers wintering in the UK (WeBS data) between 1996/97 and 2008/09. This may be due to a shift in wintering distribution, with birds not coming so far west in recent mild weather conditions, or, it may be a genuine reduction in population size. A Bewick’s Swan action planning workshop was held in St. Petersburg in September 2009 to identify threats to the birds and a Single Species Action Plan has been drafted for adoption at the African-Eurasian Waterbird Agreement Technical Committee in March 2011.
Historical information suggests Bewick’s Swans were rare in England and Wales in the 19th and early 20th centuries. During that period winter flocks occurred in the Netherlands, north-west Scotland and Ireland. Since the 1930’s the migration route has shifted southward and increasing numbers have started to winter in the English midlands (Ouse and Nene Washes) and south-west. According to Lack (1986) there are eight British Internationally Important sites and birds occur at satellite locations around each, although the British Trust for Ornithology will shortly be publishing information on waterbirds on ther website and I suspect this will show a significant change. Owen suggested there are two sites of International Importance locally; Slimbridge and the Somerset Levels, and birds could fly to Blagdon from either to feed (ringing proof that Slimbridge birds fly between BL and there is being established). Today, the distribution is more localised and they mainly winter on the Ouse and Nene Washes as well as south-west and north-west England. (n.b. cold weather influxes were said to have occurred in 1938-39 & 1955-56 – any local evidence?). Bewick’s Swans are long-lived and have been shown to reach 25 years or more, with a high adult annual survival rate exceeding 80%. The birds are monogamous, in the main, with only three cases of ‘divorce’ recorded in over 40 years of study of the population, one of which involves a female named ‘Saruni’ that visits Blagdon. I can thoroughly recommend the recent paper ‘Northwest European Bewick’s Swan’s: a population in decline’ published in British Birds vol 103, p 640 – 650 (Nov 2010) for an up-to-date perspective.
The first definite record of Bewick’s Swans visiting Blagdon Lake go back to the 12th January 1941 when four, two adult & two immature, were discovered at the Ubley end. It is likely that this referred to a family group because cygnets accompany their parents during their first winter and, on occasion, during their second winter as well (Lack, 1986). They usually arrive from mid-October onwards and stay if the water level is low enough for them to access food, if not, they leave for Chew Valley Lake or Slimbridge. Plants utilised by birds that don’t rely on food in artificial situations such as Slimbridge, include Marsh Yellow-cress Rorippa palustris, Pondweeds Potamogeton spp. and the Sweet-grasses Glyceria maxima and G. fluitans. When the water level and summer sunshine combines to produce luxuriant weed growth, Marsh Yellow-cress, several of the Pondweed species and Plicate Sweet-grass Glyceria notata all grow at Blagdon Lake (Myles et al, 2000) which may explain why the swans visit in years when the water level drops.
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Bibliography (sources of information):
- Lack, P., 1986. The Atlas of Wintering Birds in Britain and Ireland, Staffs.
- Myles, S. (Ed.) 2000. The Flora of the Bristol Region, Berks.
- Owen M. 1977. Wildfowl of Europe. London.
- Rees E.C. & Beekman J.H. Northwest European Bewick’s Swan’s: a population in decline. Brit Birds 103: 640-650, Nov. 2010.
Last update: 2nd December 2024