Europe's bird of prey population is around 55,000 lower than it should be due to contamination of their food by lead from gun ammunition, a study reported on Wednesday.
The University of Cambridge study collected data on lead levels in the livers of thousands of dead raptors to calculate the impact of poisoning on population size.
It found that Europe was missing around 55,000 adult raptors. Populations of white-tailed eagles and golden eagles were respectively 14 percent and 13 percent lower than they would be otherwise.
"The continued blanket use of lead ammunition means that hunting as a pastime simply cannot be considered sustainable unless things change," said lead author Rhys Green, a conservation scientist at Cambridge and the Royal Society for the Protection of Birds (RSPB).
"Unfortunately, efforts to encourage voluntary shifts away from lead shot have been completely ineffective so far.
"The kinds of reductions in raptor populations suggested by our study would be considered worthy of strong action, including legislation, if caused by habitat destruction or deliberate poisoning."
Species such as eagles, which are naturally long-living and rear few young per year, have been the hardest hit, the study found.
Campaigners argue that hunters could instead use a range of alternatives to lead shotgun cartridges.
Previous research by the Cambridge team found over 99 percent of pheasants killed in Britain are still shot with lead, even though hunting groups called on members to switch to non-toxic gunshot in 2020.
Two European nations -- Denmark and the Netherlands -- have banned lead shot and the European Union and Britain are both considering bans on all lead ammunition.
"The avoidable suffering and death of numerous individual raptors from lead poisoning should be sufficient to require the use of non-toxic alternatives," said study co-author Debbie Pain.
"These population-level impacts make this both doubly important and urgent."
The researchers took data gathered since the 1970s from the livers of thousands of dead raptors in 13 nations and tracked the relationship with the average numbers of hunters per square kilometre in each country.
Places with a higher density of hunters were found to have more poisoned raptors.
A similar study on the impact of leadshot on bald and golden eagles in the United States, published in the journal Science in February, found similar high levels of poisoning.