The Mute Swan Cygnus olor (Britain and Ireland populations) in Britain and Northern Ireland 1960/61 – 2000/01

Chris Spray, H. E. Rowell

    Research output: Book/ReportBook

    Abstract

    Reproduced by permission of the Wildfowl & Wetlands Trust. This report aims to describe changes in the abundance and distribution of the Mute Swan Cygnus olor in Britain and Northern Ireland since 1960/61, to compile available historical information, to provide current estimates of population size, to review published data on the ecology and biology of this species, and to describe numbers, trends and site use at the key resorts in Britain and Northern Ireland. The Mute Swan has the most southerly breeding range of the Eurasian swans. The species has a fragmented distribution, with seven recognised populations. Many birds live in areas that are mild enough for them not to have to migrate to other areas during the non-breeding season. Birds in Britain and Ireland are largely sedentary and are considered to comprise two discrete populations. The British population remained fairly stable, at around 20,000 birds, from the late 1960s to the mid- 1980s. Since the late 1980s there has been a large increase in numbers. A national census during the breeding season in 2002 estimated the population at 31,700, whilst analysis of winter counts from the late 1990s suggested a figure of 37,500. The Irish population increased in size between the 1970s and mid-1980s, since when the population has become more stable. The all-Ireland total is estimated to number 10,000, although some have suggested it may be as high as 19,000-20,000. A possible reason for the increase in population is the incidence of lead poisoning. In the late 1970s lead poisoning was shown to be the largest single cause of Mute Swan deaths in England. However, since the ban on the use of lead fishing weights in 1987 and the changes imposed on shooting in England and Wales, the number of deaths from lead poisoning has reduced greatly. Mild winters are also likely to have contributed to the general increase in swan numbers. In Ireland, however, lead still remains a problem. In Britain and Ireland, the Mute Swan is widespread on lowland wetland habitats such as slow-flowingrivers, lakes, ponds and estuaries. It also occurs on man-made wetlands (e.g. gravel pits), and in urban areas. In Britain, the greatest numbers of breeding birds are found in central, eastern and southern counties. They are largely absent from many northerly and westerly areas where high ground predominates although they flourish in the southern Western Isles and Orkney. Here, the highest breeding densities occur in lowland river basins and in isolated areas. In Northern Ireland, the highest numbers of breeding birds are found in the east parts, particularly around Loughs Neagh & Beg. The pondweeds Potamogeton, Myriophyllum and Chara are important food resources in freshwater habitats. In brackish and saltwater areas, eelgrass Zostera, tasselweeds Ruppia and various green algae are the main sources of food. Agricultural crops (oilseed rape, grasses, cereals and potatoes) are becoming increasingly important in certain areas. The species has a close association with humans, and supplementary feeding has become important in many areas. During 1996–2000, 19 sites in Britain were internationally important for the Mute Swan, regularly supporting at least 260 birds during the non-breeding season. Four sites in Northern Ireland were internationally important, holding 100 or more birds, during the same period. Information on numbers, trends and site use at these key resorts are provided within this review. Future monitoring should include the collection of demographic data to generate scientifically-robust assessments of abundance, productivity, survival and movements over a range of spatial scales. Such integrated population monitoring should be developed with the aim of understanding the population dynamics of this species. Survey during late summer is irregular, and consequently the importance of some sites for moulting birds may not be recognised. The instigation of a regular nationwide survey of Mute Swan moult flocks is recommended.
    Original languageEnglish
    PublisherWildfowl & Wetlands Trust/Joint Nature Conservation Committee
    ISBN (Print)0900806397
    Publication statusPublished - 2004

    Keywords

    • Mute swans

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