Poisoning affected one-third of waterbirds sampled and killed one in ten of those found dead
Post-mortem results of thousands of UK waterbirds reveal that poisoning from spent lead shot is still a major cause of death more than ten years after legislation was introduced to reduce the threat.
The analysis is published today alongside the results of blood samples taken from live waterbirds caught in Britain within the last two years, which show that more than one in three of the birds sampled were affected by lead poisoning.
Lead is toxic and most uses of lead have systematically been phased out over the last three decades. However lead remains the most common material for shot in the UK.
Waterbirds eat spent lead shot when feeding and taking in grit to help grind food in their gizzards. As the lead is absorbed into their bodies, it affects virtually every system. For example, it paralyses stomach muscles, causing food to become packed into the intestine, and birds can die of starvation.
Some restrictions on shooting with lead shot have gradually been introduced across the UK but they do not cover most shooting over agricultural land, where many swan and goose species graze. Studies have also shown that in England there is little compliance with the current laws with many shooters freely admitting they use lead illegally.
Martin Spray is Chief Executive of the Wildfowl & Wetlands Trust (WWT), which funded and carried out the research. Speaking from the former home of Sir Peter Scott, shooter turned conservationist and founder of WWT, he said:
“WWT has studied the effects of lead shot on ducks, geese and swans for decades, stretching back to Sir Peter Scott’s days. It is as clear today as it was then that in the UK lead poisoning from shooting kills a large number of our wild birds each year and makes many more very sick.
“Despite the law, brought in over a decade ago to protect wetland birds, nothing has changed. Clearly an effective solution is long overdue.”
Fourteen species of ducks, geese and swans were found to have died from lead poisoning. Lead poisoning accounts for at least one in ten dead waterbirds recovered across Britain between 1971 and 2010. Dead birds were found with up to 438 pieces of lead shot in their gizzards.
The researchers specifically looked for the impact of legislation designed to protect the birds. Most sizes of lead angling weight have been banned from sale since 1988. It has been illegal to shoot certain species with lead and shoot with lead over certain wetlands in England since 1999, with similar legislation being adopted in Wales, Scotland and Northern Ireland.
Across all species they could find no significant change in the proportion of birds dying from lead poisoning.
Mute swan success
However, one species, the mute swan was shown to benefit significantly from the ban on lead angling weights. The study showed that the proportion dying from lead poisoning dropped from a quarter to fewer than one in twenty.
Martin Spray explains:
“Those of us over a certain age clearly remember lead angling weights being phased out around the same time as leaded petrol. It is wonderful that the link with the recovery of mute swan numbers has been supported by our research. Unfortunately it hasn’t directly benefitted other species but if we can learn anything from the way the law was designed and implemented, perhaps they will benefit indirectly.”
Mute swans are particularly prone to swallowing lost fishing weights as they feed along the banks of rivers and lakes. Most sizes of lead weight were completely banned from sale in 1986.
Many waterbirds, such as whooper swans, graze on agricultural land where it is still legal to shoot most species with lead shot. A single shotgun cartridge contains up to 300 pieces of lead shot, almost all of which fall to the ground after being fired.
Chris Perrins, LVO, FRS, Emeritus Fellow of the Edward Grey Institute at Oxford University, has been the Queen’s Warden of the Swans since 1993. His research into lead poisoning of mute swans built the case for the restrictions on the sale of lead angling weights. He said:
“I find it extraordinary that we are still using lead [for shooting]. The Royal Commission on Environmental Pollution dealt with lead in 1983. One of its recommendations was [to phase out] all lead shooting shot and all lead fishing weights. Yet here we are nearly 30 years on and we are still using them.”
Phasing out the use of lead shot is recognised as the solution to protecting waterbirds from lead poisoning by the African-Eurasian Waterbird Agreement, an international treaty that the UK is signed up to. Lead shot is completely banned for shooting in Denmark, the Netherlands and Norway.
Martin Spray continues:
“Considering that the law currently isn’t protecting waterbirds in Britain the way it is meant to, the most practical and effective solution would appear to be to extend the restrictions on the use of lead shot to cover all shooting.
“Non-toxic alternatives are available and have been used successfully for years in countries such as Denmark. Spokespeople for the shooting community have always said that, when the evidence is forth coming, they will support practical proposals to address the threat to wildlife. We very much look forward to working with them.”
For more information please visit www.wwt.org.uk/lead.
- The paper Poisoning from lead gunshot: still a threat to wild waterbirds in Britain is published in European Journal of Wildlife Research citation DOI 10.1007/s10344-012-0666-7
- The use of lead shot was banned over the foreshore and specified (wetland) SSSIs (Sites of Special Scientific Interest) and for hunting wildfowl, coot (Fulica atra), and moorhen (Gallinula chloropus) in all areas in England in 1999 and Wales in 2002, and for hunting over wetlands (for any type of shooting activity) in Scotland in 2004 and Northern Ireland in 2009.
- In England there is evidence of non-compliance with the restrictions with 70% (n = 492) of ducks purchased from game outlets between 2008 and 2010 having been shot illegally with lead (Cromie et al. 2010). http://randd.defra.gov.uk/Document.aspx?Document=WC0730_9719_FRP.pdf
- All live birds tested for blood lead levels were caught at or near to four WWT centres in Britain: Slimbridge (Gloucestershire), Welney (Norfolk), Martin Mere (Lancashire) and Caerlaverock (Dumfriesshire).
- The species caught represented the range of feeding techniques among waterbirds: dabbling (pintail, Anas acuta), diving (pochard, aythya farina) and grazing (whooper and Bewick’s swans), all of which have previously been shown to be affected by lead poisoning.
- Blood lead concentrations usually reflect exposure to lead within 35-40 days of testing and birds were deemed to have been exposed to lead in the UK.
- Birds with blood lead exceeding 20 µg/dL were considered to have elevated concentration above background levels, indicative of lead ingestion and consistent with adverse physiological effects. The first measurable biochemical change following lead absorption appears to be inhibition of the activity of one of the enzymes (ALAD) necessary for making haem, the red pigment that carries oxygen in the blood. Inhibition of ALAD activity occurs at blood lead concentrations well below 20 µg/d, but when inhibition is sufficiently large and/or for a long period birds can become anaemic and lethargic.
- For the post-mortem analysis, pathological findings that are characteristic of lead poisoning include pale anaemic tissues (as lead affects the production of haemoglobin, the red pigment that carries oxygen in the blood) impaction of the gizzard and oesophagus with food, very little body fat, low body weight, (caused by starvation as a result of paralysis of the stomach muscles) atrophy (wasting) of the gizzard and liver, enlarged gall bladder and green staining of the vent
- Lead shot was found in the gizzards of three-quarters of the birds determined to have died from lead poisoning.
- Sometimes birds die of acute lead poisoning, after absorbing large amounts of lead, without the characteristic signs of poisoning. Therefore the proportion of birds dying of lead poisoning may be underestimated.
- The 14 species found to have died from lead poisoning were: mute swan, whooper swan, Bewick’s swan, Canada goose, western greylag goose, pink-footed goose, mallard, northern pintail, gadwall, common teal, European pochard, tufted duck, common shelduck and shoveler.
- Those species with the highest proportion of deaths recorded from lead poisoning include whooper swans (27.3%), Bewick’s swans (23%), Canada geese (16.7%) and pochard (16.7%).