LEAD-POISONING AND OTHER CAUSES OF MORTALITY IN TRUMPETER (CYGNUS BUCCINATOR) AND TUNDRA (C-COLUMBIANUS) SWANS IN WESTERN WASHINGTON

Lead poisoning and other causes of mortality of 115 trumpeter (Cygnus buccinator) and 21 tundra (C. columbianus) swans from northwestern Was hington (USA) from 1986 to 1992 are reported. Necropsies were performe d on all 136 swans, liver lead analysis conducted on 110, and differen tiation between lead and steel shot pellets recovered from gizzards in 97 swans. Shot pellets were detected in 44 (32%) of 136 gizzards. Lea d shot was recovered from 32 (33%) of 97 gizzards and steel shot from 16 (16%). Mean intensity of lead shot in gizzards was nearly five time s greater than steel shot. Thirty-nine (35%) of 110 livers had lead co ncentrations diagnostic of lead poisoning(>6 ppm, wet weight). Mean (/-SE) weight for 61 non-bad poisoned trumpeter swans was 9.8 (+/-0.30) kg, significantly heavier (P < 0.05) than 30 lead poisoned trumpeters (($) over bar x = 6.8 +/- 0.23 kg). There was no significant differen ce (P > 0.05) in weights between lead poisoned (n = 9) and non-lead po isoned (n = 12) tundra swans. Lead poisoning was the primary cause of death, accounting for 29% of the mortalities. Other causes of mortalit y identified were aspergillosis (17%), illegally shot (11%), and other traumatic factors (12%). The cause of death for 43 swans was not dete rmined. Lead poisoning from the ingestion of lead shot continues to be a principal cause of mortality in swans overwintering in northwestern Washington.