A study of the breeding Mute Swans Cygnus olor at Abbotsbury

The breeding population has varied between 18 and 130 pairs, with an increasing proportion of the breeding birds having themselves been raised in the colony.The age of first breeding is similar to that in other studies in the UK, but clutch-size is smaller and annual survival rates more variable.The number of breeding pairs is very sensitive to the over-winter adult survival rate, falling when survival is low, rising when it is high.The ages of the two members of each pair are closely correlated, even though the birds may have several mates during their life-times.