The effect of toxic lead on duck populations in the UK

On the day our new Prime Minister took over, the then Defra Secretary of State Liz Truss announced that she would not accept the advice given by the expert Lead Ammunition Group (LAG), set up by Defra, that she should phase out the use of toxic lead ammunition for sport shooting and replace it with readily available non-toxic alternatives.  The RSPB thinks that this decision is regrettable because many birds die in the UK every year when they swallow lead ammunition. Long-running attempts to reduce this toll by a partial ban on its use in wetlands have been disregarded by many shooters and have not worked, as Ms Truss accepts. I have asked one of my colleagues, Professor Rhys Green, who is a member of Lead Ammunition Group and has published widely on the effects of lead, to offer his perspective on this decision and describe results from a newly-published paper of which he is a co-author.

One of the reasons the Secretary of State gave for rejecting the LAG’s advice was that their report did not provide direct evidence of an impact on bird numbers in England of poisoning by lead ammunition.  Whether this assertion is correct or not is debatable. The report provides plenty of evidence of impacts in England that would be likely to have a population-level effects and such impacts have been documented in other countries where lead ammunition is used. However, no detailed research on population-level effects on birds in England or the UK had been published when the LAG’s report was finalised, so Defra took absence of evidence to be evidence of absence.  However, a peer-reviewed scientific paper providing evidence of such effects on duck populations in the UK had already been accepted for publication in the international journal Ibis at the time. Defra had been informed about the details of the research by the LAG two months earlier and had a copy of the accepted paper.  That paper has now been published online and is free-to-view here.

The study analysed systematic annual counts of wintering ducks in the UK over a 40-year period. It compared the average rates at which populations of different duck species have changed over time with species differences in their tendency to swallow spent lead gunshot, which they find in mud and eat in mistake for food or grit.  These differences between species are consistent in different countries, and even on different continents, and seem to be linked to the birds’ diet and the way they feed.  Duck species like gadwall that feed mainly on leaves take in fine grit particles and rarely swallow gunshot, but other species like pintail that often eat large seeds also take in large particles of grit to help grind up their food. These species, especially the pintail and pochard, but also the much commoner mallard, also often swallow gunshot pellets, which are of similar size to the seeds and grit they are seeking.  The new study found that populations of species with a propensity to swallow gunshot have been declining whilst those that rarely swallow gunshot have been increasing. Some would argue that this pattern is just a coincidence, even though it is a strikingly close relationship.  However, the study also goes on to estimate how large the differences among species in the annual death rate caused by lead poisoning should be, based upon data on the proportion of dead birds with gunshot in their gizzard. This shows that the size of the species differences in population trend are pretty close to what would be expected if they were caused solely by differences in levels of lead poisoning.  Therefore these results constitute correlative evidence that lead poisoning is causing population-level effects on birds in the UK and indicate that it alone may be  sufficient to have caused the marked population declines of some duck species.  Of these, the pochard is of special concern because it has declined so much that it is now listed by IUCN as globally threatened.

We know that a previous attempt to remove unnecessary lead from the environment in England paid off because government action to achieve it  had a population-level on an iconic bird species in England. After much unjustified protest about a supposed lack of definitive scientific evidence about adverse effects on wildlife, anglers were prevented from using lead weights for fishing in 1987.  Sounds familiar doesn’t it? On that occasion, the restrictions on the use of lead were respected, lead poisoning of mute swans decreased dramatically and their populations increased.

I think that the huge amount of evidence that lead ammunition poses an easily avoidable hazard to the health of wildlife and people already available in the LAG report and its annexes should have been sufficient to convince Defra to phase out its use.   That said, the one evidence gap the previous Secretary of State appears to have focussed on, a lack of population-level impact on birds, has now been plugged. This now presents an even clearer case for change and we trust the new Secretary of State, Andrea Leadsom, will take the opportunity for progress which her predecessor neglected.

The full report to Defra by the Lead Ammunition Group can be seen here.