Numbers and distribution of Bewick's Swan Cygnus columbianus bewickii wintering in Britain and Ireland: results of international censuses, January 1995, 2000 and 2005

摘要

The total size of the Northwest European population of Bewick's Swan Cygnus columbianus bewickii is monitored at 5-year intervals by a coordinated midwinter census throughout the swans' wintering range. This paper presents the results of three censuses undertaken in Britain and Ireland between 1995 and 2005, with a particular focus on changes in abundance and distribution. A total of 7,563 Bewick's Swans were counted in Britain and Ireland during January 1995, 7,597 in January 2000 and 7,216 in January 2005, representing a 4.6% decrease in numbers between 1995 and 2005. Numbers in both Northern Ireland and the Republic of Ireland decreased dramatically over the period, and declines also occurred in several counties in the west of England. Eastern England consistently held the largest concentrations of Bewick's Swans in Britain and Ireland, increasing by 7% between 1995 and 2005. Southeast England also saw an increase in numbers, supporting the possibility of an eastward contraction of range. The percentage of cygnets recorded in flocks in Britain and Ireland was 11.5% during January 1995, 7.6% in January 2000 and 14.4% in January 2005; mean brood size was similar in these years, ranging between 1.97 and 1.98 cygnets per successful pair. Over 90% of birds were recorded on farmland, most of which were on arable land: 58% in 1995, 87% in 2000 and 86% in 2005. Analysis of data from across Europe is needed to determine whether declining numbers in parts of Britain and Ireland reflect a shift in winterdistribution or a decrease in total population size for Bewick's Swans in Northwest Europe.