Contamination by rodenticides threatens birds of prey in Portugal

More than 80 per cent of Portuguese birds of prey may be contaminated by anticoagulant rodenticides, threatening the conservation of several species, according to a study published in November by a team from the Faculty of Sciences of the University of Lisbon (CIÊNCIAS ULisboa) and the University of Gran Canaria.

The study focuses on 210 birds of 15 species, delivered to recovery centres on the mainland and in Madeira, and reveals widespread exposure to compounds used in rodent control.

Of the total number of birds analysed between 2017 and 2024, 83 per cent showed signs of at least one anticoagulant rodenticide in their livers. In almost 60 per cent of positive cases, two or more compounds were found, increasing the risk of cumulative and potentially fatal effects.

In Madeira, the problem is even more serious: almost 90 per cent of birds showed multiple contamination, with average concentrations higher than those recorded on the mainland, suggesting more intensive use of rodenticides in pest control on the island.

Anticoagulant rodenticides are used to control rodents, causing fatal internal bleeding by preventing blood clotting. As they persist in tissues, they accumulate in predators that consume contaminated prey, posing a risk to birds of prey.

In turn, in birds these compounds can cause internal bleeding, weakness, loss of coordination and, in extreme cases, death. Even in non-lethal doses, they reduce hunting ability, increase the risk of accidents and compromise reproduction.

Among the compounds detected are Brodifacoum and Bromadiolone, highly persistent and toxic substances. Older birds show higher concentrations, evidencing the effect of bioaccumulation over the years.

Common species such as the Spotted kestrel and Barn owl can serve as sentinels, allowing the evolution of contamination to be monitored due to their wide distribution and diet based on small rodents.

The study confirms that the impact of rodenticides is no longer sporadic, but rather a persistent and widespread phenomenon, affecting several generations of birds and weakening already vulnerable populations.

The consequences for biodiversity are significant and could compromise the balance of ecosystems if essential species decline dramatically or disappear from certain regions.

The authors advocate urgent measures, including regular monitoring, restrictions on the indiscriminate use of rodenticides and the promotion of safer alternatives for rodent control, which are essential for protecting wildlife.