Lead poisoning, through the ingestion of spent lead gunshot, is an established cause of morbidity and mortality in waterbirds globally, but the thresholds at which blood levels begin to affect the physiology of birds in the wild are less well known. Here we determine the prevalence of lead exposure in whooper swans and, for the first time, identify the level of blood lead associated with initial reductions in body condition. Blood lead elevated above background levels (i.e. >20 μg dL−1) was found in 41.7% (125/300) of swans tested. Blood lead was significantly negatively associated with winter body condition when levels were ≥44 μg dL−1 (27/260 = 10%). Our findings indicating that sub-lethal impacts of lead on body condition occur at the lower end of previously established clinical thresholds and that a relatively high proportion of individuals in this population may be affected, reaffirm the importance of reducing contamination of the environment with lead shot.
We thank staff and volunteers at WWT Caerlaverock and WWT Martin Mere for their help in catching live birds for animal health testing. Particular thanks are extended to Martin Brown, Jonathan Reeves, Michelle O'Brien and Katie Beckmann for their assistance with health screening and to Alison Bloor, Kane Brides and Steve Heaven for data collation and processing. Dr Kevin Wood made helpful comments on an earlier draft of the manuscript, Dr Rob Thomas (Cardiff University) provided assistance with creating Fig. 1a and b and Robin Jones helped extract data, for which we are grateful. We are also indebted to two anonymous referees for their helpful suggestions for improving the manuscript.
- lead poisoning
- lead gunshot
- body condition