Lead burden in mute swans from Denmark

Area of Science:

• Ornithology
• Environmental Toxicology
• Wildlife Pathology

Background:

• Mute swans experienced high mortality during the 1978-79 Danish winter.
• Autopsies revealed starvation as the primary cause of death in many swans.
• Lead poisoning is a suspected but often unconfirmed cause of mortality in wild birds.

Purpose of the Study:

• To investigate the prevalence and impact of lead poisoning in mute swans.
• To assess the accuracy of autopsy diagnoses for lead poisoning.
• To determine lead levels in different tissues and their correlation with age and origin.

Main Methods:

• Autopsy of 2111 mute swans, with detailed examination of 76 selected swans and 184 ringed swans.
• Analysis of lead content in liver (wet weight) and sternum (dry weight).
• Correlation analysis of lead levels with swan origin, sex, and age.

Main Results:

• Starvation was the most common autopsy finding, but lead pellets were found in only 0.7% of gizzards.
• Lead poisoning was underdiagnosed at autopsy; 10% of ringed swans had >7 mg/kg liver lead, and 40% had elevated sternum lead.
• Lead levels varied geographically, with higher liver lead in western Jutland and lower sternum lead in southern Denmark. Age correlated positively with sternum lead.

Conclusions:

• Lead poisoning is a significant, often undetected, cause of mortality in mute swans.
• Standard autopsy methods may underestimate the prevalence of lead poisoning in avian populations.
• Geographical and age-related factors influence lead accumulation in mute swans.