The breeding biology of the mute swan Cygnus olor on the River Thames with special reference to lead poisoning

Abstract

This paper examines the breeding biology of the mute swan Cygnus olor on the River Thames, England. The study area was divided into the upper and lower Thames. Life tables were constructed for both areas to make predictions about the future status of the mute swan on the Thames and to see if there were any major differences between the two populations. It is suggested that the lower Thames population is not self-supporting and that lead poisoning through the ingestion of angler's lead weights was partly responsible. Two major differences between the populations was the greater mortality of cygnets aged between 10–20 weeks which resulted in a much lower fledging rate for the lower Thames cygnets (2·13 vs 3·79) and greater immature bird mortality aged between one and three years on the lower Thames. From the data we would predict a continued decline of the lower Thames population unless the use of lead weights is banned.