Population size, breeding success and distribution of Bewick's Swans Cygnus columbianus bewickii wintering in Europe in 1986-87

Abstract

In 1986-7 two international censuses of the European wintering population of Bewick's Swans were organised, in January and March. The total of the January census (14,600-16,000) was influenced by adverse weather, but came close to the totals reached in recent years. The census in March revealed that only a few birds are east of East Germany in the early spring migration period. Breeding success in 1986 was low. There is a large and so far unsolved discrepancy between the population size estimated in winter from censuses in Western Europe (16 to 17 thousand) and the most recent estimate of numbers at the breeding grounds in northern Russia (30 to 36 thousand).