A 39 year study of a Mute Sw an Cygnus olor population in the English Midlands.

The results of a long-term study of the Mute Sw an Cygnus olor in a 1440 / km2 area of the English Midlands are presented . During the period 1961 to 1999 the population varied between 213 and 551 birds with the numbers of pairs each spring ranging from 53 to 162 . Life histories of 1647 birds marked as cygnets in family parties or in flocks and whose date of death was also known are examined in detail. Of these birds only 11% achieved breeding status, high mortalities occurring in the first two years of life. Approximately 50% of the breeding birds had only one or two breeding seasons and over the period of the study a minority of the breeding adults produced a majority of the cygnets . Most birds were recorded first paired at two or three years old while first breeding mostly occurred at three an d four years old. Maximum successful breeding age recorded for both males an d females was 18 years . Females showed a higher degree of natal site fidelity and examples of incestuous pairings were recorded, with fertile offspring being produced. The effect of mate and territory change on breeding performance is also discussed. The study illustrates how the parameters affecting population dynamics have varied over a period in which there has been widespread national an d marked local fluctuations .

Coleman A .E., J.T. Coleman , P.A . Coleman & C.D .T. Minton 2001, Ardea 89(special issue) : 123-133