Biometrics and timing of primary moult of non-breeding Mute Swans Cygnus olor at Lake IJsselmeer, the Netherlands

Abstract

This paper examines the influence of weight and size upon the timing of wing moult of 488 non-breeding Mute Swans caught during the flightless period at Lake IJsselmeer (the Netherlands) in 1983. Primaries grew at a rate of 6.3 mm/day, but the growth rate slowed down later on. Start of wing moult showed a peak in the first ten days of July. Adult males began on average six days earlier than adult females. Weights are low, compared to other studies. Weight was strongly correlated with size. There was a slight tendency for larger sized swans to start moult earlier. The correlation between body weight and start of wing moult is highly significant, the heaviest swans started earliest. The swans lost weight over time. The low weights and weight-losses might indicate that food is limiting.