Gout as cause of morbidity and mortality of Audouin’s gull (Ichthyaetus audouinii) in southern Portugal

Audouin’s gull ( Ichthyaetus audouinii ) is a species endemic to the Mediterranean and Western Sahara, with the world’s largest breeding colony located on Deserta Island, Algarve (Southern Portugal). This study aimed to identify pathological abnormalities and drivers of mortality within this population, with the broader goal of improving our understanding of the terrestrial and marine threats faced by this species in the Algarve . Data on the admission of 878 Audouin’s gulls at RIAS − Ria Formosa Wild Animal Recovery and Investigation Center, between January 2010 and December 2023, were collected and characterized. Of these, 176 birds were necropsied, and histopathology was carried out on 4 birds. The results revealed that morbidity/mortality in the colony mainly affects juveniles (87.81% admissions) collected at the Faro/Olhão Wastewater Treatment Station and surrounding areas, manifesting as signs of weakness/malnutrition. Anatomopathological analysis revealed a predominance of renal and joint diseases, consistent with nephritis and urolithiasis, and ankylosis and arthritis, respectively. Histopathological examination showed the deposition of uric acid crystals in renal parenchyma. In 2 of the 4 cases analysed, trematode parasites with pigmented shell eggs were observed within the ureters and free in the coelom and were classified as belonging to the family Renicolidae . The data suggests gout as an important disease in this population, with both age-related and geographic components. This condition may be associated with debilitation following fledging, as juvenile birds move toward wastewater treatment facilities in search freshwater or food. It may also be related with the presence of a renal trematode parasite, unreported in this population, which may contribute to renal failure.