We captured birds in urban parks and peri-urban forests in the cities of Lugano, Zurich (Switzerland) and Napoli (Italy). The urban sites were located in urban forests (Lugano, Napoli) and in a cemetery (Zurich). Bird faecal samples were stored in a screw-capped tube (2 ml), which was previously filled with 1 ml ethanol puriss. (Sigma-Aldrich) under sterile conditions. We wore single-use nitrile gloves and used sterile toothpicks to collect solid samples. The tubes were initially stored in the refrigerator during the field campaign and no later than seven days after collection at -20°C until prepared for DNA extraction.

DNA extraction and library preparation was performed at WSL Phytopathology facilites, Sequencing was performed at Lausanne Genomic Technologies Facility (University of Lausanne; https://wp.unil.ch/gtf/) on an AVITI benchtop sequencing system (Element Biosciences). Bioinformatics was performed at the Genetic Diversity Center (ETH Zurich) using a custom pipeline.