Measurement of the demographic parameters of the Mute Swan Cygnus Olor population in the Lothians

The Mute Swan population in the Lothians has been studied since 1978. Only 15 pairs bred at that time in the study area (2,000 sq km); however, this figure increased to 55 pairs by 1993 which represented a mean annual increase of 9% per annum. The breeding population comprised 39.8% of the total population in April during the period 1978 to 1985; a decrease, to 33.9%, occurred in this proportion during the period 1986 to 1993. The aim of the study was to determine the extent to which the increase in the number of breeding pairs was due to high productivity in the Lothians, or if it was due to immigration. Adult swans and cygnets which hatched in the study area were marked with individually numbered Darvic leg…