Lead poisoning of Trumpeter Swans, Cygnus buccinator, in British Columbia, 1976-1994

Abstract

Lead poisoning from ingestion of lead shot is a cause of death of Trumpeter Swans (Cygnus buccinator) wintering on the southern coast of British Columbia. Between 1976 and 1994, 186 Trumpeter Swans were found either dead or sick in British Columbia; 87 (47%) were diagnosed with acute lead toxicosis. The largest die-off of 32 Trumpeter Swans occurred at Judson Lake in 1992. Tissues from 102 swans were analyzed for lead; 65 (64%) were classified as lead-poisoned. Lead residues detected in kidney, liver, bone, and blood samples of lead-poisoned swans averaged 30.6 mg/g, 23.7 mg/g, 18.3 mg/g and 4.4 mg/g wet weight, respectively. Ingested lead shot were detected in gizzards of 46 of the 62 lead-poisoned swans examined; number of pellets per gizzard were counted in 34 swans with an average of 16.8 pellets per bird (range:1-80, SD 17.3). Steel shot were detected in the gizzards of 18 of the 62 lead-poisoned swans examined; number of pellets per gizzard were counted in nine swans with an average of 3.3 pellets per bird (range:1-11, SD 3.2). Although the use of lead shot for waterfowl hunting has been banned in the main wintering areas of Trumpeter Swans since 1990, these birds continue to die from lead poisoning. Despite the high rate of unnatural mortality among Trumpeter Swans reported to our agency, their populations in the region currently are increasing. Lead poisoning as a threat to Trumpeter Swan populations in British Columbia is assessed.