Lead poisoning in Mute Swans Cygnus olor in Ireland: a review

Abstract

Lead toxicity in Mute Swans in Ireland was investigated, firstly by examination of dead swans and secondly by blood sampling live birds. Post mortem examination showed that almost 70% of all Mute Swans examined diedfrom lead poisoning. Two sources of ingested lead resulting in fatalities were identified: spent gunshot and lost or discarded anglers’ lead weights. Tissue lead levels were investigated in all dead birds to deter/nine any sub-lethal effects oflead. Three categories of Mute Swan mortality were identified: (I) acute lead poisoning (2) collisions and (3) other reasons. In most cases, lead concentrations in the tissues were highest according to the cause of death in order: lead poisoning > collision > other causes. Blood samples were collected from swans at six sites and the degree of lead contamination established. Over forty per cent of blood samples from one site showed elevated lead. X-ray examination of live swans revealed the source of contamination to be ingested lead pellets. Urban birds were shown to have higher lead levels than rural birds. The blood levels of rural birds were presumed to reflect background levels. Biochemical and haematological aspects of swan blood were also investigated. Reference biochemical and haematological values for ‘normal’ healthy swans were compared with those which had been contaminated with excess lead.