Factors affecting breeding success in Bewick's Swans Cygnus bewickii

Abstract

In this study the breeding success of Bewick’s Swans increased up to the age of nine years. It also increased with the duration of the pair bond Though most birds had only one mate during their lives, a proportion lost their first mates and subsequently re-mated. Loss of mate caused a temporary reduction in breeding rate. Individuals with more than one mate were less successful than those whose mates survived throughout their lives. The long term success of pairs appeared to be more strongly influenced by male characteristics, particularly size, than by female characteristics. Since dominance relationships, and hence access to food in winter and presumably, breeding territories in summer, are determined by male and not female fighting ability, this may explain the importance o f male size in determining the success of pairs.