Population models used in: Method to assess potential magnitude of terrestrial European avian population reductions from ingestion of lead ammunition

Current estimates of terrestrial bird losses across Europe from ingestion
of lead ammunition are based on uncertain or generic assumptions. A method
is needed to develop defensible European-specific estimates compatible
with available data that does not require long-term field studies. We
propose a 2-step method using carcass data and population models. The
method estimates percentage of deaths diagnosed as directly caused by lead
poisoning as a lower bound and, as an upper bound, the percentage of
possible deaths from sublethal lead poisoning that weakens birds, making
them susceptible to death by other causes. We use these estimates to
modify known population-level annual mortality. Our method also allows for
potential reductions in reproduction from lead shot ingestion because
reductions in survival and reproduction are entered into population models
of species with life histories representative of the most groups of
susceptible species. The models estimate the sustainability and potential
population decreases from lead poisoning in Europe. Using the best
available data, we demonstrate the method on two taxonomic groups of
birds: gallinaceous birds and diurnal raptors. The direction of the
population trends affects the estimate, and we incorporated such trends
into the method. Our midpoint estimates of the reduction in population
size of the European gallinaceous bird (< 2%) group and raptor
group  (2.9 – 7.7%) depend on the species life history, maximum
growth rate,  population trend, and if reproduction is assumed to
be reduced. Our estimates can be refined as more information becomes
available in countries with data gaps. We advocate use of this method to
improve upon or supplement approaches currently being used. As we
demonstrate, the method also can be applied to individual species of
concern if enough data across countries are available.