The widespread use of rodenticides in Portugal is having a profound and worrying impact on wildlife. Experts have confirmed that almost all animals from several species of birds of prey show signs of contamination. A scientific study reveals that exposure to these chemicals is no longer occasional, but a persistent phenomenon that affects a large part of the national territory, according to the Meteored portal.
The conclusion results from an investigation conducted by researchers from the Faculty of Sciences of the University of Lisbon, in partnership with the University of Gran Canaria. The work analyzed the impact of anticoagulant rodenticides on birds of prey, substances widely used to control rodent pests, especially in rural areas.
The results are clear. More than 80% of the animals analyzed were contaminated with rodenticides, a figure that researchers classify as alarming. In several species, the percentage exceeds 90%, raising serious concerns about medium and long-term survival.
Species among the most affected
Among the most exposed birds are the eagle owl, the pied kestrel and the barn owl. In all of these species, contamination levels reached values close to or greater than 90%, according to the data collected.
The study focused on 210 birds of 15 different species, collected between 2017 and 2024 in wild animal recovery centers on the Mainland and in the Autonomous Region of Madeira. Most of the individuals analyzed had rodenticide residue in their liver, a sign of secondary poisoning, says the same source.
This type of poisoning occurs when predators consume prey that have previously ingested the toxicants used to combat rodents. When entering the food chain, these substances end up reaching species that are not directly targeted by pest control.
Unpublished study in Portugal
Of the total birds analyzed, 83% showed traces of at least one anticoagulant rodenticide. In almost 60% of positive cases, two or more compounds were detected simultaneously, increasing the risk of cumulative and potentially fatal effects.
Although similar studies exist in other European countries, this is the first monitoring work of this kind carried out in Portugal, covering both the Mainland and Madeira, according to the researchers involved.
The data also reveals significant differences between regions. In Madeira, the situation is described as particularly serious, with almost 90% of these animals showing multiple contamination. The average concentrations detected were higher than those recorded on the Mainland, which suggests a more intensive use of rodenticides in pest control in an island context.
Toxic substances and prolonged effects
According to the same source, among the compounds identified, brodifacoum and bromadiolone stand out, highly persistent and toxic rodenticides. These chemicals cause internal bleeding by preventing blood from clotting and remain in the tissues for long periods.
Accumulation over time explains why older birds have, on average, higher concentrations. Even when they do not cause immediate death, these compounds cause serious effects, such as weakness, loss of coordination and reduced hunting ability.
According to researchers, sublethal doses can also increase the risk of collisions, hinder reproduction and weaken populations that already face other environmental threats.
Sentinel species and experts’ warnings
According to , the biologists involved in the study argue that common and widely distributed species, such as the lesser kestrel and the barn owl, can function as sentinel species to monitor the evolution of contamination in Portugal.
“These results demonstrate that rodenticides used to control rodent pests are entering wildlife food chains, which puts these species at risk and requires mitigation measures to reduce impacts,” said Sofia Gabriel, study coordinator and researcher at the Center for Ecology, Evolution and Environmental Change.
The study confirms that the impact of rodenticides is transversal and prolonged over time, affecting several generations of birds. This additional pressure can compromise the balance of ecosystems, especially if key species drastically decrease or disappear from certain regions.
Faced with this scenario, the authors advocate the adoption of urgent measures, including regular monitoring, limiting the indiscriminate use of rodenticides, promoting safer alternatives for rodent control and raising awareness among populations, in order to reduce risks to biodiversity in Portugal.
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