Lead poisoning in the Spanish eagle population of the DonÌƒana, SW Spain : an ecological risk assessment
Doñana National Park in south-west Spain is one of the last remaining strongholds of the Spanish Imperial eagle Aquila adalberti, which is one of the world’s rarest birds with only around 150 pairs remaining. Lead poisoning is known to be a problem that affects other eagle species, and the purpose of this thesis is to determine whether this is a potential problem for the Doñana population of eagles. Bird exposure to lead in this area is estimated to come from two main sources, soil and sediment lead from upriver mining operations including the 1998 Aznalcollar toxic spill, and resident lead shot due to long-term hunting activity. a soil lead distribution model is constructed for the whole Doñana, using known principles of pollution deposition in combination with satellite imagery analysis and a training dataset of soil samples dating from 1983 to the present. A lead shot distribution model is also constructed for the whole Doñana, using a simple rule-based approach to estimate the maximum niche of availability for this lead source. A Monte Carlo simulation model is developed to model the processes of transfer of lead to eagles via their prey species Greylag geese Anser anser and Mallard ducks Anas platyrhynchos. The model predicts potentially high (5.2%) probability of an eagle being lead poisoned. A GIS-based ecological risk assessment model quantifies the spatial pattern of lead shot ingestion for Greylag geese and Mallard ducks and grades each of Doñana’s eagle territories according to their lead risk value. The sensitivity, uncertainty and error for all of the above models are assessed in detail. Finally, future research needs are identified, conservation actions prioritised and management decisions recommended.