Abstract
Background This work summarizes the confirmed causes of death of twenty-five free-ranging Eurasian brown bears ( Ursus arctos arctos ) from the Cantabrian mountain range submitted for necropsy in Asturias and Castilla y León (northwestern Spain) from 1998 to 2018. Results Causes of death were classified based on (i) pathological findings and (ii) caused by “human intervention” or “non human intervention”. In four cases (16%) it was not possible to determine the cause of death due to the bad preservation of found remains or insufficient tissue availability. Based on pathological findings seven out of the 21 (33.3%) brown bears in which the cause of death could be determined died due to infectious diseases (clostridiosis n =4 or infectious canine hepatitis n =3), two (9.5%) due to exertional (degenerative) myopathy (one of those bears also showed clostridiosis) and one due to strychnine poisoning (4.8%), neoplasia (4.8%) or mushroom poisoning (4.8%). The remaining animals died due to traumatic lesions (including fights or infanticide), shooting or wire snare. Mortality data was also classified by deaths caused by “human intervention” or “non human intervention”. The death of one bear showing exertional myopathy after handling was not ascribed to any of the former classifications. Six out of the 20 (30%) brown bears died as a consequence of “human intervention” due to illegal hunting (wire snare hunting n =3 or shooting n =2) and, strychnine poisoning ( n =1). In contrast, fourteen (14/20, 70%) brown bears died by “non-human intervention”; nine of them (9/20, 45%) due to traumatic lesions (fights n =4, traumas n =3 or infanticide n =2), three (3/20, 15%) due to infectious canine hepatitis caused by canine adenovirus type 1 (CAdV-1) infection, one (1/20, 5%) due to cholangiocarcinoma and another one (5%) due to mushroom poisoning. Conclusions This study shows that the main causes of death in Eurasian brown bears are those caused by infectious diseases. In contrast to previous data on free-ranging bears for the first time infectious diseases appear as an important cause of death. These data are valuable and may help in the conservation and management of this recovering population.