Blood lead levels in wintering and moulting Icelandic whooper swans over two decades

Abstract

Lead poisoning of waterfowl through the ingestion of spent gunshot and discarded anglers' weights continues to be a problem worldwide. We took blood samples from 363 whooper swans Cygnus cygnus at wintering sites in Britain and Ireland and at moulting sites in Iceland during 2001-2005, and analysed them for total blood lead. Lead levels were generally low in swans in Iceland; 6% of samples exceeded 1.21 mmol L À1 , the level indicative of elevated lead and above background levels. The proportion of swans with elevated lead was much higher in the wintering range, varying between 43 and 70% at three sites monitored over the winters 2003/2004-2005/2006, and with blood lead levels ranging up to 19.6 mmol L À1 . The highest levels were in samples taken from swans in Scotland, with a mean value of 3.0 mmol L À1 , but nevertheless they indicated a marked decrease compared with blood lead levels measured for whooper swans at the same site 20 years ago. There also appeared to be a significant long-term decrease in the proportion of swans with elevated blood lead in Iceland, from 60% of birds in 1984 to 8% in 2005, although this may be due to the birds being caught in different parts of Iceland. The most likely source of elevated lead in whooper swans is spent gunshot. Management measures to reduce the impact of lead in the environment on the birds are discussed.

Poisoning from lead gunshot: still a threat to wild waterbirds in Britain

“…This is consistent with previous studies which also recorded elevated lead levels (i.e. >1.21 μmol/L) in adult whooper swans caught at both sites (Spray and Milne 1988;O'Connell et al 2008). In areas of high exposure (e.g.…”

“…The poisoning and death of Bewick's, mute and whooper swans from lead in Britain and Ireland is well documented (O'Halloran et al 1988b;O'Halloran, unpublished results;Brown et al 1992;O'Connell at al. 2008), and lead gunshot have been frequently found in lead-poisoned swans (Owen and Cadbury 1975;Mudge 1983;Spray and Milne 1988;O'Halloran et al 1988a, b;O'Halloran unpublished results;O'Connell et al 2008).…”

“…High mortality rates have been recorded in Canada geese in the USA, poisoned by lead gunshot ingested during foraging in crop fields (Szymczak and Adrian 1978). Whooper and Bewick's swans may require particularly large quantities of grit when feeding on more indigestible foods such as potatoes, corn and barley and are thus perhaps more likely to ingest spent gunshot (O'Connell et al 2008). The poisoning and death of Bewick's, mute and whooper swans from lead in Britain and Ireland is well documented (O'Halloran et al 1988b;O'Halloran, unpublished results;Brown et al 1992;O'Connell at al.…”

“…Poisoning caused by lead is a widely accepted and well-documented global problem for humans, domestic animals and wildlife and remains an important cause of morbidity, mortality and suffering in waterbirds and terrestrial birds (Pain 1996;Scheuhammer and Norris 1996;Beintema 2001;Mateo 2009;Pain et al 2009). In Britain, lead poisoning has been studied since the 1960s and reported in many species of waterbird (Olney 1960;Thomas 1980;Birkhead 1982;Mudge 1983;Perrins et al 2003;O'Connell et al 2008).…”

“…Elevated blood lead levels (i.e. >20.0 μg/dL) were recorded in 79.7 % of whooper swans (Cygnus cygnus) caught at wintering sites in England 5 to 6 years after the introduction of legislation, and in 61.4 % of this species in Scotland, 1 year following legislation, with ingestion of spent lead shot attributed as the most likely cause (O'Connell et al 2008).…”