A new research article published in the Archives of Environmental Contamination and Toxicology (see below) has revealed that substantial proportions of four species of avian scavengers found in Switzerland had elevated levels of lead in their body tissues, most likely due to ingestion of fragments of lead ammunition.
Study on lead levels
The researchers measured lead concentrations in liver and bone samples taken from the two main alpine avian scavengers, the golden eagle and bearded vulture, throughout the Swiss Alps and two avian scavengers from the Swiss lowlands, the red kite and the common raven. The samples were taken from a total of 127 bird carcasses including 67 golden eagles, 5 bearded vultures, 45 red kites and 10 common ravens. Five golden eagles and one bearded vulture showed signs of having been illegally shot (i.e. the presence of encapsulated lead pellets found in the body), while collision with power lines or other cables was the one of the most common causes of death alongside injuries sustained during territorial fights, predation or other causes.
Increased lead levels in Alpine avian scavengers
Three of the five bearded vultures had bone lead concentrations indicative of background exposure (i.e. < 10 μg/g) and two had bone lead concentrations that correspond to abnormally high exposure compatible with severe clinical poisoning (i.e. > 20 μg/g). Fourteen of the 46 golden eagles had lead concentrations compatible with lethal lead poisoning, while samples from only one of the red kites and none from the ravens reached lethal levels. However, samples from eight red kites and four out of ten ravens had lead levels indicative of subclinical to clinical poisoning (10-20 μg/g).
The study revealed that avian scavengers in the Alps generally have higher bone lead concentrations than lowland species, with levels in golden eagles and bearded vultures from the Swiss Alps being very high compared with data from studies conducted in other areas. For example, two of the five bearded vultures had very high bone lead concentrations (58.90 μg/g and 100.04 μg/g) compared to a previous study in the Alps which found that only three (20%) bearded vulture samples had concentrations higher than 6.75 μg/g, and another study from the Pyrenees which found only 1 out of 43 individuals with bone lead concentrations indicative of chronic poisoning (>20 μg/g). The authors therefore suggest that scavengers in the Swiss Alps are more heavily exposed to lead compared with other areas and raise concerns about the general health of the avian scavenger community in Switzerland, including in the lowlands where there was evidence for frequent exposure above background levels.
Impacting bearded vultures
The authors highlighted the particular susceptibility of bearded vultures to lead poisoning and its role as a leading cause of mortality. Bearded vultures are likely to retain lead particles in their stomachs for longer periods than other raptors because their main diet of bones requires longer digestion times, and their highly acidic digestive system also causes efficient dissolution and absorption of lead particles into the body tissues, increasing the risk of lead poisoning. Elevated levels of lead can affect flight heights and movement rates in birds, possibly increasing the risk of collisions and reducing foraging efficiency, as well as longer term impacts on physiology and reproduction rates.
Consequently the authors emphasize the importance of lead poisoning as a serious threat to the bearded vulture population and encourage the rapid uptake of lead-free ammunition for hunting, either voluntarily or through enforced legislation, to relieve these important avian scavengers from the lethal and sublethal effects of lead exposure.
Protecting bearded vultures
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.
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 projects where hunters try non-lead ammunition are being carried out, and in two areas of Maestrazgo which has just began a bearded vulture reintroduction project the Generalitat Valenciana has banned the use of lead ammunition.
We here at the Vulture Conservation Foundation unreservedly supports the promotion of the use of lead-free ammunition for hunting purposes and this article adds to the growing body of evidence to support immediate action against the dangerous effects of lead poisoning on vultures and other scavengers.