Recent analysis of blood lead levels in whooper swans has shown that ingestion of lead continues to be a threat for wildfowl in the UK. The proportion of birds with elevated blood lead at three sites in the UK ranged from 43–70 % in winters 2002/2003–2004/2005.
Lead poisoning from the ingestion of spent shotgun pellets continues to threaten wildfowl in the UK and globally and is an issue WWT is tackling with this project.
- To analyse the blood lead levels in whooper swans in order to determine whether legislative measures such as the banning of lead in anglers’ weights has led to a decrease in exposure for the species
- To monitor whether regulations prohibiting the use of lead ammunition for shooting wildfowl over wetlands in UK countries have been effective
How WWT is helping
Scientists from University College Cork, WWT and Iceland undertook a collaborative project to assess levels of sub-lethal lead poisoning in whooper swans by analysing blood samples taken on the UK wintering grounds and in the breeding range in Iceland.
Blood lead levels generally remain elevated for days to weeks following exposure, and were considered to reflect exposure at or near the sampling site.
Data collected were compared with those of Spray & Milne (1988) from Iceland and Scotland in the mid 1980s. The analyses found that blood lead concentrations were generally low in swans in Iceland, where up to 6% of samples exceeded the 1.21 μmol L-1 level indicative of elevated lead.
The proportion of swans with elevated lead concentrations was much higher in the wintering range than on the breeding grounds, varying between 38% and 88% at the three sites monitored over the winters 2002/2003–2004/2005, and with blood lead concentrations ranging up to 19.5 μmol L-1. The highest concentrations were in samples taken from swans in Scotland, with mean values of up to 2.5 μmol L-1.
Nevertheless this represented a marked decrease compared with blood lead concentrations measured for whooper swans at the same site 20 years ago, when >90% of swans sampled had >1.21 μmol L-1 of lead in their blood.
This decrease is not fully unexplained. Although regulations prohibiting the use of lead gunshot over wetlands were not introduced until March 2005 in Scotland, close to the completion of our study, the decrease may to some extent reflect the ban on the sale of lead in anglers’ weights, which was introduced in Scotland in 1986.
The highest proportion of birds with elevated blood lead concentrations (mean = 70%) was found at the English site. In contrast to Scotland, legislation banning the use of lead gunshot for shooting wildfowl or over designated wetland sites was introduced in 1999 in England.
While we had no historic data with which to compare blood lead levels in England, the high incidence of elevated concentrations is perhaps not surprising.
In an earlier study, we found poor compliance with the legislation in at least one section of the shooting community in England two years after the ban, with 68% of purchased Mallard having been shot illegally with lead (Cromie et al. 2002).
Lead pellets are thought to take 100–300 years to break down in the environment, and although the most recently deposited are likely to be the first ingested, there could well be a time lag before the impacts of regulations, even when complied with, are observed.
Additional monitoring is required to evaluate whether regulations prohibiting the use of lead ammunition for shooting wildfowl and/or over wetlands, now adopted by all UK countries, have been effective.
Cromie, R.L., Brown, M.J., Hughes, B., Hoccom, D.G. & Williams, G. 2002. Prevalence of shot-in pellets in Mallard purchased from game dealers in England in winter 2001/2002. In: RSPB. 2002. Compliance with the Lead Shot Regulations (England) during winter 2001/02. RSPB, Sandy, UK.
O’Connell, M.M., Rees, E.C., Einarsson, Ó., Spray, C.J., Thorstensen, S. & O’Halloran, J. 2008. Blood lead levels in wintering and moulting Icelandic Whooper Swans over two decades. Journal of Zoology 276: 21-27.
Spray, C.J. & Milne, H. 1988. The incidence of lead poisoning among Whooper and Mute Swans Cygnus Cygnus and C. olor in Scotland. Biological Conservation 44: 265–281.
Financial support to University College Cork was provided by the Higher Education Authority, Ireland, and the Environmental Research Institute, University College Cork, Ireland
- Icelandic Institute of Natural History
- Olafur Einarsson
- Sverrir Thorstensen
- University College Cork
- University of Dundee