Predictive framework for estimating the risks to raptors from ecologically relevant exposure to second generation anticoagulant rodenticides

Globally, populations of many raptor species are declining for reasons including exposure to chemical contaminants. Second Generation Anticoagulant Rodenticide (SGAR) residues are commonly found in the livers of raptors, indicating dietary exposure and potentially secondary poisoning. There is a gap in our understanding of SGAR exposure for raptors at different life stages and under different usage regimes.

We develop a new modelling framework for non-target species to refine the commonly applied risk assessment using the common kestrel (Falco tinnunculus) as a case study. Our scenarios simulate high and low rodent consumption by raptors with high and low SGAR usage, of four different rodenticides at different raptor life stages. The risk to raptors was evaluated in reference to sublethal and lethal effect thresholds used by regulators.

Our model suggests exposure to Brodifacoum exceeds the threshold for lethal and sublethal effects. Breeding adults and nestlings are at risk of sublethal effects from Difethialone and the mixture of Bromadiolone and Difenacoum exposure. This is concerning because Brodifacoum and Difethialone usage seems to be rising globally due to increased resistance of rodents to other SGARs. Difethialone represents cumulative risk in scenarios previously not a risk, reaching the threshold in a week Avoiding SGAR usage during the raptor breeding season would reduce the likelihood and impact of secondary SGAR poisoning. Our framework can be used to assess different exposure scenarios for SGARs and raptors in ecological meaningful contexts to guide SGAR usage and regulation.