Toxic legacy: The hidden impact of anticoagulant rodenticides on Portuguese raptors

Anticoagulant rodenticides (ARs) are widely used for rodent control, with a significant risk of secondary poisoning in non-target wildlife, particularly raptors. This study presents the first broad monitoring effort in Portugal, by assessing AR bioaccumulation levels in raptor species that entered Portuguese wildlife recovery centres between 2017 and 2024, both from mainland and Madeira Island. We analysed liver samples from 210 individuals from 15 species, representing four families: Accipitridae, Falconidae, Strigidae, and Tytonidae. Hepatic residues of first- (FGARs) and second-generation anticoagulant rodenticides (SGARs) were quantified via HPLC/MS-MS. Our findings revealed that 83 % of raptors accumulated at least one second-generation AR compound in their liver, with brodifacoum being the most prevalent, followed by bromadiolone. No first-generation ARs were detected. Geographical differences were evident: raptors from Madeira Island exhibited higher levels of multiple ARs, including notably high concentrations of difethialone. All six candidate sentinel species showed similar levels of AR bioaccumulation. However, Bubo bubo, Falco tinnunculus, and Strix aluco had AR detection rates exceeding 90 %. Falco tinnunculus and Tyto alba are widespread across the country and Madeira archipelago, making them effective sentinels for AR monitoring in Portugal. Additionally, older raptors showed a higher likelihood of accumulating greater concentrations of AR residues, which is consistent with the bioaccumulation effect by consumption of multiple rodent prey over their lifespan. Our results highlight significant contamination of Portuguese raptors with ARs, underscoring the urgent need for monitoring and mitigation efforts to safeguard these critical sentinel species from the harmful effects of rodenticides.