Raptor health as an indicator of ecosystem health: a novel toolbox for conservation

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.