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investigations of temporal and spatial relationships between
ammunition ingestion/poisoning and shooting seasons or
intensity, isotopic studies to investigate the source of elevated
tissue lead concentrations; studies of changes in survival in wild
birds with different levels of gunshot ingestion, and others.
These studies have been conducted in many countries across
the world, primarily over the last 65 years and have shown that
lead poisoning from ammunition sources is geographically
widespread and causes substantial suffering and mortality in
many avian taxa.
Lead from ammunition is known to affect a wide range
of biological and physiological systems in birds and other
vertebrates, and birds can die rapidly after ingesting lead from
ammunition (acute poisoning), or gradually following lower
levels of exposure or absorption, or repeated exposure (chronic
poisoning). Lead poisoning from ammunition lead was first
recorded in the UK well over a century ago (Calvert 1876) and
reports of lead poisoned birds grew rapidly from the 1950s
onwards in the UK and globally. Wildfowl are the best studied
taxa, but where lead ingestion has been investigated in other
taxa that feed in shot-over areas, including terrestrial gamebirds,
it has generally been found. Lead poisoning in predatory
and scavenging birds, primarily raptors, has also been widely
reported, although relatively few studies have been conducted
in the UK.
In the UK, we can broadly estimate the numbers of birds
from certain avian taxa that are likely to die as a direct result
of ingesting lead gunshot every winter. These estimates are
based upon published gunshot ingestion incidence in different
species, and corrected for hunting bias (i.e. that hunters are
more likely to shoot lead poisoned birds), turnover of gunshot
in the alimentary canal, and increases in mortality as a result
of ingesting different numbers of gunshot. These estimates
suggest that 50,000-100,000 wildfowl are likely to die each
winter (i.e. during the shooting season) as a direct result of lead
poisoning. Wildfowl that die outside of the shooting season
will be additional, as will birds dying from the indirect results of
lead poisoning. Several hundred thousand wildfowl may suffer
welfare effects.
Estimates of mortality for terrestrial gamebirds in the UK are
likely to be less accurate and precise due to fewer studies, but
we estimate that about 600,000 terrestrial gamebirds are likely
to have ingested gunshot at any one time and many times
more throughout the shooting season. All birds that ingest lead
gunshot may suffer some welfare effect, and a proportion of
them, perhaps of the order of hundreds of thousands, are likely
to die from lead poisoning each year.
There is strong evidence from studies in North America
and elsewhere that a sometimes substantial proportion of
predatory and scavenging birds die also from lead poisoning.
A few studies from the UK have reported lead poisoning in
certain raptor species, and the source and pathways exists for
a wider range of species to be affected, but further research on
this is needed.
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