Causes of morbidity and mortality in free-ranging Eurasian lynx (Lynx lynx) in Switzerland, 2000–2022

Health monitoring based on post-mortem examination is essential for the management of endangered animal species. This is especially true for reintroduced species living in small populations with low genetic diversity, such as the Eurasian lynx (Lynx lynx) in Switzerland. Thanks to systematic post-mortem examinations, the Institute for Fish and Wildlife Health (FIWI), University of Bern, has acquired a comprehensive view of the lynx health in Switzerland. This study provides an updated overview of the causes of morbidity and mortality in the Eurasian lynx in Switzerland from 2000 to 2022. A total of 346 necropsied lynx (found dead, euthanized, or culled) were included in this study, and a cause of death (COD) was identified in 318 of them (91.9%). Overall, the main COD was blunt trauma (n = 183, 52.9% - largely vehicular collision). Starvation, resulting from the separation of dependent juveniles from their mother, was the second most frequent COD (n = 63, 18.2%). Fatal infectious diseases were relatively low (n = 32, 9.2%). However, we documented some significant pathogens such as canine distemper virus (CDV) and metastrongyloid nematodes. Illegal killing was confirmed in 23 cases (6.6%). Of note, illegal killing is likely underestimated in this study, given that radio-collared lynx were found to be proportionally more often illegally killed than the unmonitored ones found by chance. Furthermore, most individuals were found to be affected at least by one non-specific, mild to moderate inflammatory process of unknown origin, such as interstitial pneumonia (n = 59) or interstitial nephritis (n = 25). Additionally, cardiac changes of variable severity were observed in 125 lynx, and severe soft tissue mineralization was detected in 10 individuals. The frequency of these findings warrants further investigation. Thus, this study confirms the importance of systemic post-mortem examination and general health surveillance of free-ranging Eurasian lynx in Switzerland, in support of translocation projects, conservation of the species, and to provide a better understanding of their pathologies.