Abstract
Pesticides remain among the most significant threats to biodiversity and natural ecosystems. Non-invasive methods, such as the analysis of bird faeces, have shown great potential for detecting pesticide exposure. In this study with a new approach, we analysed faecal sacs from nestlings of Blue tits (Cyanistes caeruleus) and Great tits (Parus major) to gain deeper insights into pesticide contamination during the breeding period. Samples were collected from three distinct sites near Münster, Germany. In total, we detected 65 substances from 57 different pesticides, as well as caffeine, with pesticides present in 16.07% of the 168 samples. Concentrations varied between species and sites and were higher for fungicides and insecticides in nests located closer to agricultural fields. While no direct effects on reproductive success were found, our results underscore the potential of faecal sac analysis as a valuable tool for spatially resolved pesticide monitoring. The novel, non-invasive approach to pesticide monitoring offers crucial exposure data on juvenile birds during their sensitive breeding period.