Chemical pollution affects birds of prey more in urban areas than in rural areas

Birds of prey, at the top of the avian food chain, are particularly sensitive to pollutants. They serve as true sentinels of pollution in food webs. Researchers have found that the intensification of agricultural practices exposes these species to chemicals that are partly responsible for the decline in bird populations across Europe. In reality, however, raptors in urban areas are at greater risk of contamination.   Over the past 50 years, the intensification of agricultural practices has led to a significant decline in the populations of birds inhabiting farmland in Europe. In addition to factors related to increasing urbanization—such as reduced landscape heterogeneity and habitat fragmentation—the exponential use of chemicals in agriculture has actively contributed to this decline. Among the most affected populations, birds of prey are on the front lines, as they are particularly sensitive to the bioaccumulation and biomagnification of toxic compounds in the environment. As apex predators at the top of the food chain, birds of prey serve as true sentinels of ecosystem health and contamination in food webs. Researchers therefore examined the levels of chemical pollutants found in birds of prey, originating from products used in both agricultural and urban settings (anticoagulant rodenticides, pharmaceuticals, and plant protection products; insecticides, herbicides, and fungicides). The goal was to assess the current threat these products pose to European ecosystems. They analyzed the livers of several species of raptors living in rural or urban areas in Germany: the red kite (Milvus milvus), the northern goshawk (Accipiter gentilis), and the Eurasian sparrowhawk (Accipiter nisus), as well as the white-tailed eagle (Haliaeetus albicilla) and the osprey (Pandion haliaetus), in order to account for potential aquatic exposures. The findings indicate that rodenticide contamination is a very real threat to raptors in Germany. However, it is not the populations in rural areas that are most at risk. Exposure to rodenticides appears to be higher in urban habitats. Red kites and goshawks appear to be the most affected by this contamination, due in particular to species-specific characteristics. The detection of rodenticide levels in white-tailed eagles suggests that exposure may not be limited to terrestrial food webs. However, further studies, including those using dietary substitutes, are needed to identify the exact sources of exposure. Similarly, the observed link between the likelihood of rodenticide exposure and the degree of urban ground cover warrants further investigation into terrestrial trophic transfers and associated risks in urban ecosystems. Ibuprofen (14.9%) and fluoroquinolones (2.3%) were also detected in samples collected from dead raptors. This finding highlights that their widespread use in large quantities, combined with manure fertilization and incomplete wastewater treatment, leads to emissions that result in residues in the environment. In contrast, most of the plant protection products analyzed and currently in use were not detected in raptors, suggesting that widespread contamination in the study area is unlikely. However, the rapid metabolism of some of these products in biological tissues suggests that further analyses—using blood samples collected from nestlings, for example—would be more appropriate in the future for assessing spatio-temporal exposure. Taken together, the results demonstrate that exposure to rodenticides poses a threat to certain birds of prey, particularly those living in urban habitats. Researchers are particularly concerned about the extent of contamination, which could spread well beyond terrestrial food webs.