a poisonous metal present in a variety of commercial products, and as
a pollutant from industrial activities. Lead has become an
environmental contaminant in many areas of the world, and in many
habitat types both urban and rural. When ingested or inhaled, the body
"mistakes" lead for calcium and other beneficial metals, and thus
incorporates lead into nerve cells and other vital tissues. Results in
humans and wildlife include neural degeneration, modification of
kidney structure and bone, inhibition of blood formation and nerve
transmission, and numerous other harmful manifestations (Eisler 1988).
Death may occur acutely, or the individual may emaciate as a result of
digestive paralysis (Locke and Thomas 1996). Clinical symptoms
associated with blood lead concentrations exceeding one part per
million may include depression, lethargy, vomiting, diarrhea,
nonregenerative anemia, anorexia, blindness, and seizures (Locke and
Thomas 1996, Kramer and Redig 1997). Accumulating evidence of the
effects of sublethal exposure points to permanent adverse effects upon
cognitive function in human children with histories of blood levels
averaging 0.1 parts per million - a level formerly considered benign
(Canfield et al. 2003).
Scientific evidence of the effects of
lead on human health has brought forth large scale restrictions on its
use in the United States, including the prohibition of lead in
gasoline and paint. Responses on behalf of wildlife have been less
forthcoming, but Bald Eagle consumption of contaminated ducks and
geese contributed to the 1991 ban on lead shot for waterfowl hunting
in the United States (United States Department of the Interior 1986).
Other countries have instituted similar measures. Evidence of lead
exposure in arctic subsistence hunters who continue to use lead shot (Dewailly
et al. 2001, Johansen et al. 2003) suggests that the ban in behalf of
eagles may have benefited humans as well.
Lead ammunition is
still used in America for purposes other than waterfowl harvest, and
the extent to which lead is secondarily ingested by wildlife and
humans has been the subject of some recent investigations. Mourning
doves, for example, confuse shotgun pellets for grit and grain around
hunted stock ponds and accordingly die in large numbers (Schulz et al.
2002). Harmata and Restani (1995) found lead in the blood of 97% of 37
Bald Eagles and 85% of 86 Golden Eagles captured as spring migrants in
Montana during 1985-1993; they implicated lead bullet fragments in
ground squirrel carcasses as one source. Pattee et al. (1990) reported
that among 162 free-ranging Golden Eagles captured during 1985-86 in
southern California, 36% had been exposed to lead. Six of nine dead
eagles in Japan died of lead poisoning, and five had lead bullet
fragments in their stomachs (Iwata et al. 2000). Lead ingestion was a
principal cause of recorded death in wild California Condors prior to
the mid-1980s when the population was brought into captivity (Wiemeyer
et al. 1988).
Field studies by
The Peregrine Fund from 2000 to the present show that ingestion of
lead rifle bullet fragments and shotgun pellets from animal remains is
likely the only significant obstacle to the establishment of the
California Condor in the wilds of Arizona and Utah. Evidence includes
(1) high rates of lead exposure and required treatment, (2) the
presence of lead fragments or shot in radiographs of condors and their
food, and (3) temporal and spatial associations of condors with the
remains of gun-killed animals (Parish et al. in press, Hunt et al.
2006, Hunt et al. in press). During the 2006 hunting season, 90
percent of 57 free-ranging condors showed evidence of lead exposure,
and four died of it, including a proven breeder almost 12 years old.
This represents an 11% mortality rate for birds five years old or
older, a meaningful consideration given the high sensitivity of condor
populations to mortality within the older age categories. The
additional unknown proportion of condors that would have died without
treatment renders doubtful the survival of the species in the wild
without continuing, intensive management.
of condors by radio tracking and blood testing, together with
ancillary studies of lead prevalence in gun-killed deer and other
animals, have produced new insights regarding the pervasive nature of
lead contamination in scavenger food webs. One must now consider, on a
global scale, the scope of sickness, death, and demographic impact
inflicted upon a myriad of species by a contaminant now so easily
substituted with less toxic alternatives. The invention of highly
efficacious non-lead bullets and pellets during recent decades
parallels the discovery of leadís widespread impact on wildlife (and
coincides with additional studies documenting lead's effects on
humans), and it is evident that conditions now favor large scale
An important step
in understanding this problem is the gathering together of relevant
knowledge and scientific progress on these important topics. Nowhere
would such an assembly of facts and interpretation be more fruitful
than in the proceedings of a conference of world experts. The
Peregrine Fund therefore proposes to bring them together in May of
2008, and to publish the proceedings and resolutions soon thereafter.