Breeding performance of an Irish Mute Swan Cygnus olor population

Mute Swans breeding in Dublin, Ireland were studiedfrom 1983 to 1989. Only 46% o f birds bred in the season in which they were five y ears old.The mean clutch size was 6.7.About 80% o f clutches hatched.The mean brood size was 4.2 per nest at hatching and 2.7 per 'nest ' at the age o f three months.A shortage o f suitable territories seemed to limit recruitment to the breeding population and to promote the use o f inadequate territories, especially on estuaries, in (usuallyfutile) breeding attempts.Urban breeders tended to be younger than rural ones.Ireland, at the western edge of the Palearctic range of the Mute Swan Cygnus olor (Cramp & Simmons 1977), has a milder climate than the species encounters elsewhere.Ringing has shown that this population is virtually closed (Spencer & Hudson 1978, Spray 1981a, Collins 1985).A study of the dynamics of the Mute Swan population in the Dublin region commenced in March 1983.This paper gives the results to date on the age at which birds begin to breed and on breeding productivity.It examines breeding performance in various habitat types and compares breeding productivity in urban and rural environments.