New research shows that birds of prey populations across Europe are suppressed by lead poisoning from hunting ammunition
Toxic lead ammunition used by hunters has long been shown to kill raptors – or birds of prey – by contaminating their food. A new investigation carried out by scientists from Germany and the United Kingdom uses data on lead levels in the livers of thousands of dead raptors to calculate the impact of lead poisoning on their population size. This first-ever analysis shows that Europe is missing at least 55.000 adult raptors because of lead poisoning, with populations of white-tailed sea eagles 14 % lower and golden eagles 13 % lower than they would otherwise be. The research is published in the scientific journal “Science of the Total Environment”.
Poisoning caused by preying on or scavenging animals shot by hunters using lead ammunition has left the populations of many raptors – or birds of prey – far smaller than they should be, according to the first scientific investigation to calculate these impacts across Europe. When birds such as eagles and red kites scavenge carcasses or eat injured animals with fragments of toxic lead from hunting ammunition embedded in their bodies, they accumulate the lead in their body, causing severe or fatal poisoning and then suffer slow and painful deaths. Smaller doses have been shown to alter behaviour and physiology even if they do not kill.
Now, scientists from the University of Cambridge and the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) have used data on lead levels in the livers of over 3.000 raptors found dead in more than a dozen countries to calculate the extent to which poisoning by lead ammunition has affected Europe’s raptor populations. The scientists estimate that, for ten raptor species, poisoning from lead ammunition alone has resulted in an absence of around 55.000 adult birds from European skies.
Worst affected are species such as eagles that are naturally long-lived, rear few young per year and start breeding later in life. More familiar species such as the common buzzard and the red kite would also be significantly more numerous without the effect of lead accumulation. For example, the calculations suggest that Europe’s white-tailed sea eagle population is 14 % smaller than it would have been without more than a century of exposure to lethal levels of lead in some of its food. This is closely followed by the golden eagle and griffon vulture with populations 13 % and 12 % smaller than they would otherwise have been. Northern goshawk numbers are 6 % smaller, and both red kite and western marsh harrier populations are 3 % smaller. Common buzzard populations are 1.5 % smaller, equivalent to almost 22.000 fewer adults of this widespread species, say the scientists. They estimate that the overall European population of ten raptor species is at least 6 % smaller than it should be, solely as the result of poisoning from lead ammunition.
Leading author Prof Rhys Green, a conservation scientist at the University of Cambridge and the Royal Society for the Protection of Birds (RBSP), says that a range of alternatives to lead shotgun cartridges and rifle bullets are widely available to hunters and work well. However, efforts by UK hunters’ organisations to instigate voluntary bans on lead shot in hunting have had almost no effect.
“In Germany, only 4 out of 16 federal states have banned the use of lead-based rifle ammunition for hunting”, says Leibniz-IZW scientist and co-author Dr Oliver Krone. “Also, lead ammunition is prohibited in state-owned forests in all German states (Länder), in federal forests in several states, and in national parks and areas owned by nature conservation agencies. This unclear situation leaves significant space for the continued use of lead rifle ammunition, since the vast majority of hunting grounds such as most forests and farmlands are privately owned. Partial solutions for this problem are not sufficient to end the negative effect of lead poisoning on raptor populations in Germany, a nation-wide solution to the problem would be necessary.” The use of lead shotgun ammunition to hunt waterfowl at waterbodies has been banned by almost all German states, but this ammunition is still used to hunt species such as pheasants, hares, pigeons, partridges, rabbits or foxes. “Just as with rifle ammunition, the use of lead shotgun ammunition is allowed in most situations and banned in only some”, concludes Krone.
Currently, only two European nations – Denmark and the Netherlands – have banned lead shot countrywide. Denmark plans to follow this up with a ban on lead rifle bullets. Both the European Union and the UK are considering legal bans on all lead ammunition because of its effects on wildlife and the health of human consumers of wildlife meat, but many hunting groups oppose this, according to the scientists.
Many raptors are poisoned when they scavenge from dead animals killed with lead ammunition. This can be a whole carcass lost or abandoned by hunters, or – for example – the guts of a hunted deer and wild boar, discarded to avoid bacterial contamination of the meat and to reduce the weight the hunters need to carry. As well as vultures, which rely on scavenging entirely, many other raptors also scavenge when the opportunity arises, including eagles, buzzards and kites. Other species, such as falcons and goshawks, are exposed to toxic lead through preying upon live animals with lead embedded in their bodies from being shot and injured. Systematic radiographs of wild ducks in the UK and of wild geese in Germany showed that about a quarter to a third of live birds have lead shots in their bodies. Ducks or pigeons injured in this way are less likely to evade predatory birds.
“It’s taken decades for scientists from across Europe to amass sufficient data to enable us to calculate the impacts of lead poisoning on raptor populations,” says co-author Prof Debbie Pain from the University of Cambridge. “We can now see just how substantial the impacts on populations can be for some of our most charismatic and vulnerable species – species that are protected by EU Regulation and the UK Wildlife & Countryside Act. The avoidable suffering and death of numerous individual raptors from lead poisoning should be sufficient to require the use of non-toxic alternatives. These population-level impacts make this both doubly important and urgent.”
For the latest analysis, the scientists used population modelling techniques to calculate how big Europe’s raptor populations would have been, were it not for the destructive impact of a single “additional mortality factor”, lead poisoning from ammunition. They took data gathered since the 1970s from the toxicological investigations of livers of thousands of dead raptors in 13 nations and tracked the relationship with “hunter density”: average numbers of hunters per square kilometre in each country, using data from the European Federation for Hunting and Conservation. Unsurprisingly, places with a higher density of hunters had more poisoned raptors. The scientists used this relationship to predict the proportion of poisoning birds of prey in countries without data from bird livers from where “hunter density” was known. Their results indicate that a country with no hunters using lead ammunition would have virtually no lead-poisoned raptors.
Green, Pain and Krone say their estimates are conservative, not least as data on poisoned raptors is limited and difficult to gather. For many European raptor species, including some of the rarest ones, there were insufficient data to estimate how great the risk is.
Dr Oliver Krone
Scientist in the Department of Wildlife Diseases
Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW)
phone: +49 (0)30 5168212
Green RE, Pain DJ, Krone O (2022): The impact of lead poisoning from ammunition sources on raptor populations in Europe. Science of the Total Environment.