Whooper Swan Cygnus cygnus egg production in different nesting habitats in Finland

Abstract

A total of 112 Whooper Swan nests with eggs were examined in Finland. Of these 40 were on the fens (mobile pairs) and 72 on ponds or lakes with rich vegetation (sedentary pairs). The clutch size of sedentary pairs, 5.08, was statistically significantly higher than that of mobile pairs, 4.40, (F = 10.231, P<0.01). Also, the relationship between clutch size to egg volume seems to be different in the two habitats. There did not appear to be any difference between laying date in different habitats. Horsetails are typical in lakes and ponds and are of great value as the food of Whooper Swans. A possible reason for the higher clutch size of sedentary pairs may be the quality o f the food eaten by the female during laying, especially the high protein content of growing horsetails.