Wild bird health surveillance through citizen science: a pilot Garden Bird Disease Observatory in Catalonia (NE Spain)

Garden birds are wild bird species that frequent gardens and urban areas in search of food and shelter. In recent years, several have undergone population declines and been affected by several serious diseases. This study evaluates the results of a pilot citizen science-based network programme in Catalonia (NE Spain) that aims to monitor disease in garden birds, investigate causes of morbidity and mortality and identify risk factors that could facilitate control measures. Between November 2021 and February 2023, 96 reports of sick or dead birds belonging to 30 different species were gathered, primarily from the Torreferrussa Wildlife Health Centre (43%), direct public contact (32%) and the Ornitho.cat platform of the Catalan Institute of Ornithology (10%). The remaining reports (14%) originated from other sources of information. Rapid response, good feedback and consistent dissemination over time were key to ensuring citizen participation. Trauma – mainly associated with anthropogenic factors such as glass collisions – was the most frequent cause of death (41%), followed by road traffic accidents, and predation. Infectious diseases accounted for 14% of deaths, including outbreaks of Newcastle Disease Virus/Orthoavulavirus-1 and isolated cases of salmonellosis, mycobacteriosis, coligranulomatosis, knemidocoptic mange, fungal pneumonia and septicaemia. Other relevant findings included nephropathy, feather cysts, nutritional hyperparathyroidism, tick infestations, haemosporidian infections, endoparasitosis (trematodes, nematodes, cestodes and coccidia) and beak abnormalities. This study highlights the effectiveness of combining citizen science and pathological surveillance for monitoring mortality in urban birds. Our findings also reveal key anthropogenic and infectious threats and underscore how long-term monitoring and public involvement can play an essential role in managing wildlife health in urban environments.