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Mateo et al. (2001), González and Hiraldo (1988), Castaño López
(2005), Mateo et al. (1999), Gonzalez (1991), Garcia and Viñuela
1999, Donázar et al. (2002).
Krone et al. (2009) performed experiments on white-tailed
eagles in which iron nuts of various sizes were inserted into
carcasses or discarded viscera form which they fed. The eagles
always avoided ingesting nuts of 7.7 mm diameter or larger, but
ingested some of the nuts smaller than this (2.7 – 6.0 mm). For
the smallest size of nuts used in the experiment (2.7 mm), 80%
of the nuts presented were eaten. These nuts were considerably
larger than most of the fragments of ammunition-derived metal
seen in X-radiographs of deer carcasses and discarded viscera.
Knott et al. (2010) found that 83% by weight of the radio-dense
fragments they found in deer viscera had a diameter less than 1
mm and the largest fragment seen on the radiographs was only
slightly larger than the smallest nuts used in the experiment.
Hence, this experiment suggests that in a similar situation in
the wild, were fragments from lead ammunition to be present
in a carcass, many of these could be readily ingested whilst
scavenging on the remains of game animals.
Several methods exist to infer the origin of elevated tissue lead
concentrations and leadpoisoning inpredatory and scavenging
birds. The most detailed isotopic studies have been conducted
on California condors and they indicate that elevated lead
exposure in free-living condors is mostly consistent with lead
from ammunition rather than other sources (Church et al. 2006,
Finkelstein et al. 2010, 2012, Rideout et al. 2012). Departure of
blood lead isotope signature from the background pattern in
free-living birds increased progressively as the total blood lead
concentration increased, moving towards the isotopic signature
of lead ammunition and bullet fragments retrieved from lead
poisoned condors (Church et al. 2006, Finkelstein et al. 2012).
Isotopic analysis also illustrates that ammunition-derived lead
is the likely provenance of elevated tissue lead concentrations
in a number of Steller’s sea eagles and white-tailed eagles
in Hokkaido, Japan (Saito 2009 – with rifle ammunition
implicated). Legagneux et al. (2014) found that blood lead
concentrations in the raven, a scavenging species, increased
over the moose Alces alces hunting season in eastern Quebec,
Canada, and that birds with elevated blood lead levels had
isotopic signatures that tended towards those of ammunition.
Several other studies, including on red kites in England (Pain
et al. 2007) and white-tailed eagles in Sweden (Helander et
al. 2009) show isotopic signals consistent with ammunition
sources in birds with elevated tissue lead, although they do
not exclude all possible non-ammunition sources of lead.
Lead concentrations in the livers of a sample of red kites and
sparrowhawks Accipiter nisus found dead in Britain were not
elevated and lead isotope signatures were distinct from that
of leaded petrol, marginally overlapped with that for coal, and
overlapped more with those for lead ammunition (Walker et al.
2012). The isotopic signatures in this study may reflect the fact
that liver concentrations were low and could have resulted from
multiple diffuse sources.
A number of studies of scavenging and predatory birds have
investigated the relationship between tissue (generally blood)
lead levels and spatial and temporal variation inexposure to food
contaminated with ammunition-derived lead. Green et al. (2008)
showed that blood lead concentrations in California condors
tended to rise rapidly when satellite-tagged condors spent
time during the autumn deer-hunting season in areas with high
levels of deer hunting, but that visits to these same areas outside
the hunting season, and visits to other areas with low levels of
deer hunting at any time of year were not associated with rises
in blood lead levels. Craighead and Bedrosian (2008) found that
47% of blood samples in ravens in the USA collected during
the large game (mainly deer) hunting season had elevated
blood lead (>10 µg/dl), compared with 2% outside the hunting
season; these results were consistent with those of Legagneux
et al. (2014) cited above. Kelly et al. (2011) compared blood lead
concentrations in golden eagles and turkey vultures Cathartes
aura prior to and one year following implementation of a ban (in
2008) on the use of lead ammunition for most hunting activities
in the range of the California condor in California; lead exposure
in both species declined significantly after the ban. Similarly,
Pain et al. (1997) found that geometric mean blood lead levels
were 3-4 times higher in free-flying live-trapped western marsh
harriers during the hunting season in France than outside
the hunting season. Kelly and Johnson (2011) found that the
blood lead concentrations of turkey vultures in California were
significantly higher during the large game hunting season than
outside it. Gangoso et al. (2009) found that the geometric mean
concentration of lead in the blood of Egyptian vultures in the
Canary Islands was about four times higher during the hunting
season than outside it. While these studies show consistent
results, it is nonetheless worth noting that most studies which
contrast theblood leadconcentrationof birdswithinandoutside
the hunting season underestimate the underlying difference in
exposure to lead. This arises because blood lead remains high
for some time, often several weeks, after the ingestion of lead
has ceased. Consequently, some blood samples obtained in the
Lead poisoning of wildlife in the UK