Saving wetlands for wildlife & people
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Background 
The Mute Swan Cygnus olor has the most southerly breeding range of the Eurasian swans (Wieloch et al. 1997). It is patchily distributed but locally common across temperate regions of the Palearctic, from Western Europe to northeast China (Scott & Rose 1996).
Two populations of Mute Swan are recognised in Great Britain and Ireland: the British population, which breeds and winters in Britain, and the Irish population, which breeds and winters in Ireland. In Britain, the greatest numbers of breeding birds are found in central, eastern and southern counties. They are largely absent from northerly and westerly areas where high ground predominates, although they flourish in the southern Western Isles and Orkney. In Northern Ireland, the highest numbers of breeding birds are found in the east, particularly around Loughs Neagh & Beg. Generally, Mute Swans in Britain and Ireland are sedentary except for localised movements to coastal waters, especially in cold weather, and to freshwater marshes and agricultural fields (Ogilvie 1986a; Kirby et al. 1994; Chisholm & Spray 2002). Movements between southeast Britain and the continent occur occasionally, mainly during very harsh winters (Spray et al. 2002). A small number of Mute Swans are known to move from the Western Isles of Scotland to Northern Ireland and the Irish Republic (Spray 1981; O'Halloran & Collins 1985). However, these are largely immature birds, and there is no evidence of any return movements (C. Spray pers. obs.). In Britain and Ireland, the Mute Swan is commonly found on lowland wetland habitats such as slow-flowing rivers, lakes, ponds, and estuaries. Large numbers can also be seen in public parks or on rivers used for public recreation, where they benefit from food provided by the public (Kirby et al. 1994). Traditionally, 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. However, in recent decades agricultural crops (oilseed rape, grasses, cereals and potatoes) have become more frequently used as forage, especially oilseed rape and improved grasslands. This has brought the species into conflict with farmers, due to the alleged damage the birds cause (Trump et al. 1994; Spray et al. 2002). Most complaints occur between late winter and early spring, when the birds' natural foods are scarcest (Owen et al. 1986). Mute Swans are highly territorial (mature birds without a territory do not usually breed). Once a territory has been established, birds defend it rigorously to prevent intruders from trying to set up a territory nearby (Kear 1972). Territory size probably depends on the quality of the habitat, with lower densities in the less favourable parts of their range (Ogilvie & Delany 1993). Unlike migratory swans, a large number of British and Irish Mute Swans maintain their territories throughout the year (Kirby et al. 1994). Scott (1984) showed that winter temperature and available food supply were the critical factors that cause territorial pairs to abandon a site. However, territories sometimes become less exclusive in winter, and pairs occasionally share with large flocks of immature birds. The number of Mute Swans in Britain remained fairly stable throughout the 1960s and 1970s. However, the British population underwent a large increase from the mid-1980s. The Irish population also increased in abundance between the 1970s and mid-1980s, but has since remained relatively stable. A possible reason for the increase in abundance is the reduction in 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 (Kirby et al. 1994). 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 (Rowell & Spray 2004). In Ireland, lead is still widely used in fishing and hunting as there is no legislation to control its use. Decreased winter mortality during milder winters, improvements in water quality and an increase in the availability of suitable breeding habitats, as a result of the creation of gravel pits and ponds, are also believed to have contributed to the increase in numbers. The Wetland Bird Survey (WeBS) records Mute Swans at wetland sites throughout Great Britain and Ireland. Although WeBS coverage of estuaries and large inland waterbodies is good, the entire population is not recorded by these counts since many birds are present on small waters, streams, flooded fields and ditches (Kirby et al. 1994). To address this issue, five spring censuses of Mute Swans have been carried out between 1955/56 and 2002 to obtain a better estimate of population size as well as to provide information on the breeding and non-breeding components of the population, and distribution and habitat choice during the breeding season. The species is also monitored in the breeding season in the UK by the Breeding Bird Survey (BBS) and the Waterways Breeding Bird Survey (WBBS), both organised by the British Trust for Ornithology (BTO).
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