- To ascertain the contribution of ammunition as a source of lead exposure and its contribution to effects, including mortality, to scavenging birds.
- To examine whether there are viable pathways of exposure for scavenging birds to other environmental sources of lead.
- To assess the toxicity to birds of alternate metals used in ammunition.
After examining multiple lines of evidence, scientists concluded that lead ammunition is the most frequent cause of lead exposure and poisoning in scavenging birds in the United States. The suite of evidence to support this conclusion includes:
- the extent of lead ammunition currently used in hunting and its tendency to fragment,
- the behavioral ecology and physiology of scavenging birds,
- scavenging birds’ susceptibility to lead as exhibited in controlled dosing studies,
- the diagnosis of lead poisoning in birds by well-established tissue thresholds and clinical signs,
- the recovery of ingested lead fragments or pellets from exposed birds,
- observations of birds feeding on contaminated carcasses,
- isotopic analyses relating tissue concentrations to ammunition,
- patterns of mortality coincident with hunting seasons, and
- the lack of substantial evidence for other sources of lead.
While the Service will not, as of now, be using this information to create any new policies, we did review the toxicity of alternate metals that can replace lead, and found that they are currently available and present limited environmental threats.