Raptor health as an indicator of ecosystem health: a novel toolbox for conservation
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Date
31/07/2021Author
Peniche Peyron, Gabriela
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Abstract
Monitoring the health of wildlife is a vital element of environmental stewardship, and
there are benchmark examples of crucial interventions involving predators, and especially
birds of prey (raptors; Order: Accipitres). Such work can involve ecological, behavioural,
veterinarian and toxicological approaches. The scale of work can vary from studying a few
individuals of a species through to national and global surveillance programmes over long
time periods. Such work contributes to our understanding of the health of individuals,
species populations and indeed wider ecosystems. Predators are commonly used as
indicator species due to their position at the top of the food chain and their susceptibility to
processes of bioaccumulation and biomagnification. Furthermore, the relatively small sizes
of many predator populations means that they can be more easily and closely monitored,
enabling the determination of the causes of decline or poor health at local, regional or wider
scales.
This project assesses the health of raptor populations in Scotland, through the
development of a series of tools. Health examination and blood sampling of live individuals
of a single species, the golden eagle (Aquila chrysaetos), were used to develop blood
reference intervals as Tool 1 to assess individual health. Biometrics obtained from the same
birds were combined to develop Tool 2 for sexing nestlings and later help inform population
sex ratios. Post mortem examinations of many raptor species were used to create Tool 3 to
assess health at a single point in time, and to see if this could be used to discern the health
of raptor populations. Finally, Tool 4 was devised to analyse essential and toxic elements,
pesticides, pharmaceuticals and poisons in raptor tissues and blood to obtain an overview of
chemicals present in birds at the top of the food chain.
These four tools were used to help us understand the health of raptors. The work
relied heavily on a wide network of people, both raptor specialists as well as members of the
public, in providing carcasses for post mortem examination and analyses of samples.
Detailed work on golden eagles centred on developing Tool 2 found that no biometric
measure/identifier, single or in combination, was capable of determining the sex of chicks
aged 7.5 weeks or less (despite many fieldworkers claiming they can readily determine the
sex of eagle chicks).
Examination of 170 carcasses of 15 species of raptor found that trauma was the main
contributor to death. Detailed screening for chemicals in 111 individuals from 13 raptor
species detected cadmium in all species tested and in over 40% of individuals. Lead was
detected in 13 of 14 species tested and in more than 80% of individuals. Mercury was
detected in all individuals and both mercury and lead concentration increased across the
country from east to west, matching a higher incidence of respiratory disease and higher
mortality of golden eagle chick towards the west of the country. Arsenic was found in five of
14 (35.7%) species tested. A combination of the most commonly used rodenticides was
detected across eight raptor species, with highest levels found in buzzards (Buteo buteo) and
barn owls (Tyto alba). No intact pharmaceutical or poison compounds were detected across
the sampled population. Not all pharmaceutical or poison metabolites could be screened for.
It is hoped that this work can be developed as part of long term monitoring of raptors
in Scotland. In particular, the tools offer promise for detecting local and regional patterns in
raptor and ecosystem health in Scotland.