Metal and arsenic contamination of a terrestrial top-predator, the black kite (Milvus migrans), after the Aznalcóllar mine spill (southwestern Spain): Temporal trends and fitness consequences

Abstract

Top-predators serve as sentinels of ecosystem health due to their sensitivity to environmental contamination. However, our understanding on how contaminants affect individual fitness is still scarce, especially for long-lived species. Here, we measured blood concentrations of 4 metals (Cd, Cu, Pb, and Zn) and one metalloid (As) in black kite (Milvus migrans) adults from Doñana National Park (SW Spain) following a major mine spill. Besides temporal variation (1998–2001) in metal and As concentrations, we tested how metal and As profiles changed across individuals in relation to their sex, age or breeding status, and examined whether metal and As concentrations affected individuals' fitness (breeding success and mortality). We found that, overall, blood concentrations of Pb, Cd and As increased throughout the study period in black kites, mirroring the progressive increase previously reported for their main prey. Both sex (Cu and Zn) and breeding status (Zn and Pb) affected element concentrations. Non-breeding (floater) females had higher levels of Zn than their breeding counterparts. The same pattern of higher contamination in floaters was observed for Pb, which might be related to differences in diet and foraging activity between breeders and floaters. The percentage of the individuals with Pb concentrations that exceeded toxicity thresholds (> 200 μg/L) was relatively high (15.4 %). Moreover, Pb concentrations were negatively correlated to males' breeding success. We found no clear evidence to support metal and As effects on survival or life expectancy after accounting for environmental and individual sources of variation. Our results highlight the importance of long-term studies of marked individuals in wild populations; detailed knowledge of ecological processes relevant to these populations, combined with measures of contaminant exposure at individual level, provides opportunities to enhance our understanding of its fitness effects and potential demographic consequences.