A newly published article in the journal Science of the Total Environment has reviewed 62 scientific articles from across the globe that have studied lead contamination in vultures and condors. The findings confirm that exposure to lead, primarily through the ingestion of lead ammunition, poses a serious threat to many vulture populations.
Threat of lead poisoning
Lead poisoning from ammunition used by game hunters is an often-overlooked threat to vultures, but is widespread and may have population-level impacts and the article presents some useful insight into the impact of lead contamination.
When an animal is shot, a lead bullet fragments widely throughout the carcass. Often the carcass and viscera of these animals are left behind and out in the open by hunters. Whilst feeding on the carcasses of animals that have been shot vultures can then ingest lead fragments.
Lead exposure studies
The article found that the vast majority (92%) of the reviewed articles were published after 2001, showing that lead exposure in vultures has only been studied relatively recently. There was also a geographical disparity in research effort, with 72% of the articles presenting results from North America and Europe.
Thirteen out of 23 species of vultures and condors were included in the studies, and 88% of the articles identified individuals with lead concentrations above thresholds for contamination in their sampled tissues. Despite this, lead contamination is considered a major threat for just 8% (2/23) of the vulture species categorized by the IUCN Red List.
Impacts of lead contamination
The most frequently suspected source of lead contamination was ingestion of lead ammunition when vultures feed on carrion or waste products from animals killed by hunters. The authors recommend that further standardized research should be completed in order to confirm this link to enable the creation and implementation of suitable legislation to remove this threat to vulture populations and other wildlife.
The health impacts of lead contamination in vultures include the inhibition of metabolic functions and negative effects on the nervous, reproductive, immune, urinary and digestive systems. Acute and chronic poisoning can result in weakness, inhibited movement, paralysis, inhibited respiration, behavioural abnormalities, weight loss, immune system disruptions and bone mineralization. Ultimately, in many cases lead toxicosis results in death. However, the authors highlight that there is a lack of knowledge about how susceptible different vulture species are to lead contamination, and they call for further research in this field using methods and criteria that are standardized across all future studies.
The final sentences from the conclusions of the article illustrate the serious threat that lead contamination poses to vulture populations, and the urgent need to address it through further research to inform conservation policies and actions:
“There is an urgent need to evaluate the effect of this contaminant on vulture demography, since some species may be undergoing important reductions on their populations due to this threat. A silent threat such as lead may produce long-term population decreases that are difficult to detect or reverse and thus, merits special attention.”
In recognition of the impacts of lead poisoning or contamination, we here at the Vulture Conservation Foundation and other conservation organisations are working with hunters and governments towards passing laws and regulations to minimise this threat.
Lead poisoning was recognised as an important issue in the Vulture Multi-species Action Plan a global plan for the conservation of 15 species of vultures, co-developed by the Vulture Conservation Foundation which called for the phasing out of its use. As well as causing toxisis as the authors of the study highlighted some common effects on vultures are actually sub-lethal, reducing their breeding performance and negatively altering their movement patterns,and increasing the likelihood of collisions with power lines.
Across Europe there have been several initiatives to reduce the use of lead ammunition and promote lead-free hunting practices. In the Italian Alps the use of lead ammunition has been banned in the Stelvio National Park and Sondrio Province. At Hohe Tauern National Park in Austria, in the Pyrenees, and as part of our GypConnect and GypHelp LIFE conservation projects, at the Cévennes National Park in the French Massif Central, and in Haute-Savoie, pilot project where hunters try non-lead ammunition are being carried out.
Following all this, we are incredibly pleased to hear the news that the Generalitat Valenciana have banned the use of lead ammunition in two areas in Maestrazgo, a very positive move to protect vultures there including birds released as part of the new bearded vulture reintroduction project.